fix: list a subagent's background Bash commands

Claude Code sends no tool_use_result with a subagent's tool results, so a subagent's background Bash command was never recognized: its terminal was reported exited at once and it was missing from the subagent's background list. The task_started that names the Bash call comes before the result, so use it when the result has no structured backgroundTaskId.
fix: list Monitor calls in the session's background work (#1538 )
2026-11-06 17:31:36 +00:00 · 2026-11-06 17:36:50 +01:00 · 2026-11-06 12:12:58 +01:00 · 2026-11-05 22:07:42 +01:00 · 2026-11-05 12:01:11 +00:00 · 2026-11-04 20:04:11 +01:00
122 changed files with 8430 additions and 956 deletions
--- a/.github/workflows/binaries.yml
+++ b/.github/workflows/binaries.yml
@@ -0,0 +1,125 @@
+# Builds the standalone executables (scripts/build-binary.mjs) and smoke-tests
+# each one on a runner of its own platform. Each archive holds
+# `claude-agent-acp` and the Claude CLI (`claude`) it runs from its directory.
+# CI calls this to check that every target still builds and starts; the
+# release calls it with `upload: true` and attaches the archives to the GitHub
+# release.
+name: Binaries
+
+on:
+  workflow_call:
+    inputs:
+      upload:
+        description: Upload each archive as a workflow artifact for the release job.
+        type: boolean
+        default: false
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: Binary (${{ matrix.target }})
+    runs-on: ${{ matrix.runner }}
+    timeout-minutes: 20
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - target: bun-linux-x64
+            runner: ubuntu-latest
+            archive: claude-agent-acp-linux-x64.tar.gz
+          - target: bun-linux-arm64
+            runner: ubuntu-24.04-arm
+            archive: claude-agent-acp-linux-arm64.tar.gz
+          # npm skips the musl package on a glibc host, so these are
+          # cross-built and smoke-tested in an Alpine container.
+          - target: bun-linux-x64-musl
+            runner: ubuntu-latest
+            archive: claude-agent-acp-linux-x64-musl.tar.gz
+            musl: true
+          - target: bun-linux-arm64-musl
+            runner: ubuntu-24.04-arm
+            archive: claude-agent-acp-linux-arm64-musl.tar.gz
+            musl: true
+          - target: bun-darwin-x64
+            runner: macos-15-intel
+            archive: claude-agent-acp-darwin-x64.zip
+          - target: bun-darwin-arm64
+            runner: macos-latest
+            archive: claude-agent-acp-darwin-arm64.zip
+          - target: bun-windows-x64
+            runner: windows-latest
+            archive: claude-agent-acp-windows-x64.zip
+          - target: bun-windows-arm64
+            runner: windows-11-arm
+            archive: claude-agent-acp-windows-arm64.zip
+
+    defaults:
+      run:
+        shell: bash
+
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
+
+      - uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1
+        with:
+          node-version: "lts/*"
+          check-latest: true
+          cache: "npm"
+
+      # Unpinned: each build is smoke-tested on its platform before it uploads,
+      # so a Bun release that breaks the executable fails here instead of
+      # shipping. Pin a version if one ever regresses past the smoke test.
+      - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
+        with:
+          bun-version: latest
+
+      - run: npm ci
+
+      - name: Install the musl Claude CLI package
+        if: ${{ matrix.musl }}
+        run: |
+          version="$(node -p "require('./node_modules/@anthropic-ai/claude-agent-sdk/package.json').version")"
+          npm install --no-save --force "@anthropic-ai/claude-agent-sdk-linux-${RUNNER_ARCH,,}-musl@$version"
+
+      - name: Build
+        run: |
+          echo "Built \`${{ matrix.target }}\` with Bun $(bun --version)" >> "$GITHUB_STEP_SUMMARY"
+          node scripts/build-binary.mjs --target ${{ matrix.target }}
+
+      - name: Smoke test
+        if: ${{ !matrix.musl }}
+        run: node scripts/smoke-binary.mjs
+
+      # Claude Code's Alpine requirements: libgcc and libstdc++.
+      - name: Smoke test (Alpine)
+        if: ${{ matrix.musl }}
+        run: |
+          docker run --rm -v "$PWD:/work" -w /work node:lts-alpine \
+            sh -c 'apk add --no-cache libgcc libstdc++ >/dev/null && node scripts/smoke-binary.mjs'
+
+      - name: Archive
+        if: ${{ inputs.upload }}
+        env:
+          ARCHIVE: ${{ matrix.archive }}
+        run: |
+          cd dist-bin
+          if [[ "$ARCHIVE" == *.zip ]]; then
+            if [[ "$RUNNER_OS" == "Windows" ]]; then
+              pwsh -Command "Compress-Archive -Path claude-agent-acp.exe,claude.exe -DestinationPath ../$ARCHIVE"
+            else
+              zip "../$ARCHIVE" claude-agent-acp claude
+            fi
+          else
+            tar czf "../$ARCHIVE" claude-agent-acp claude
+          fi
+
+      - name: Upload
+        if: ${{ inputs.upload }}
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
+        with:
+          name: ${{ matrix.archive }}
+          path: ${{ matrix.archive }}
+          retention-days: 7
+          if-no-files-found: error
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -44,3 +44,7 @@ jobs:

      - name: Run tests
        run: npm run test:run
+
+  binaries:
+    name: Binaries
+    uses: ./.github/workflows/binaries.yml
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -88,6 +88,38 @@ jobs:
          npm publish
          echo "version=$version" >> "$GITHUB_OUTPUT"

+  # Standalone executables for the GitHub release, stable releases only. They
+  # don't gate the npm publish: a failed build leaves the release without
+  # binaries, and re-running the failed jobs attaches them.
+  build-binaries:
+    name: Build binaries
+    needs: [release-please]
+    if: ${{ needs.release-please.outputs.release_created == 'true' }}
+    # The called workflow only reads the repository; upload-binaries does the write.
+    permissions:
+      contents: read
+    uses: ./.github/workflows/binaries.yml
+    with:
+      upload: true
+
+  upload-binaries:
+    name: Attach binaries to the release
+    runs-on: ubuntu-latest
+    needs: [release-please, build-binaries]
+    permissions:
+      contents: write
+    timeout-minutes: 15
+    steps:
+      - uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333 # v8.0.2
+        with:
+          path: artifacts
+          merge-multiple: true
+      - name: Upload to the release
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          TAG: ${{ needs.release-please.outputs.tag_name }}
+        run: gh release upload "$TAG" artifacts/* --clobber --repo "$GITHUB_REPOSITORY"
+
  # Same shape as publish-npm. Tagging is a separate job, so nothing here needs
  # write access to the repository.
  publish-npm-preview:
@@ -199,7 +231,11 @@ jobs:
          echo "Tagged \`v$VERSION\` at \`$SHA\`" >> "$GITHUB_STEP_SUMMARY"

  trigger-registry-update:
-    needs: [publish-npm, publish-npm-preview]
+    # upload-binaries too, so a stable release's archives are attached before the
+    # registry reads the release: it takes each archive's sha256 from the release
+    # assets when it bumps the version. It only waits; a failed or skipped upload
+    # (every preview) doesn't stop the dispatch.
+    needs: [publish-npm, publish-npm-preview, upload-binaries]
    # Both channels dispatch this: the registry has its own handling for preview
    # versions. The two never fire together — a release merge publishes stable and
    # skips the preview, and every other push does the reverse — so the registry sees
--- a/.gitignore
+++ b/.gitignore
@@ -3,4 +3,5 @@ dist
 .DS_Store
 .claude/*.local.*
 CLAUDE.local.md
-.idea/
+.idea/
+dist-bin
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "0.99.1"
+  ".": "0.101.0"
 }
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -16,13 +16,85 @@ npm run format        # prettier --write
 CI runs `format:check`, `lint`, `build` and `test:run`. Run `npm run check` before
 opening a PR.

-## Code comments
+## Coding guidelines

-Keep comments straightforward, concise, and concrete. Say what the code does and
-why, in plain terms: name the actual state, call, or failure involved instead of
-alluding to it. Prefer a short concrete example over an abstract description.
-Don't use vague phrases like "keeps it honest" or "the residual case" that make
-the reader reconstruct the meaning.
+- Keep edits consistent with the surrounding code's formatting, naming and idioms.
+- Keep comments concise and concrete. Name the actual state, call or failure
+  instead of alluding to it, prefer a short example over an abstract
+  description, and avoid vague phrases like "keeps it honest". A comment or doc
+  must be true on every code path it describes, and a doc that lists what a
+  result omits or rejects must name the actual cases.
+- When a request can't be served, throw a `RequestError` whose message says what
+  happened and what to do (e.g. "Try again when the turn ends"). Don't drop the
+  request silently.
+- Don't report success for work you start without awaiting it. If the detached
+  call can still refuse and its `.catch` only logs, check the refusal condition
+  first or report the failure to the client.
+- A result must not depend on what an earlier call happened to cache. A request
+  right after a restart, with cold caches, must return the same thing as one
+  after a warm-up.
+- If code relies on an ordering or call sequence that nothing enforces (e.g. an
+  echo arriving before the result), say so in a short comment.
+
+## Architecture and design fit
+
+- Before coding, read the code the change plugs into and find the module that
+  owns the state or concept. Build on that module, not beside it.
+- Don't add new features or components to `acp-agent.ts`. If no existing module fits the new
+  code cleanly, create a dedicated one that owns the feature's state and logic,
+  and keep the change in `acp-agent.ts` to the calls that wire it in.
+- Prefer extending an existing mechanism over adding a new one, even if it takes
+  a small refactor (moving a helper, generalizing a function). Add a parallel
+  path, special case or flag only when the existing structure can't support the
+  change.
+- Before writing new logic, check whether it already exists in a sibling handler
+  of the same flow or in a helper that works with the same data, and reuse it.
+  Paths that handle the same input must apply the same rules through the same
+  code: the live stream and the `session/load` replay, the command list and
+  command dispatch, `prompt` and `steer`. Two copies of one check drift apart.
+- Put guards, filters and cleanup in the module that owns the state, so every
+  caller gets them. If guards, flags or fallbacks pile up in one place,
+  restructure instead of adding another.
+- If a result is meant to match another request's output, reuse that request's
+  logic.
+- The adapter serves ACP v1 and v2. A change that is not meant for one protocol
+  version only must work correctly in both. `src/v2/` converts v2 requests to v1
+  and reuses the v1 logic; keep v2-only differences in the conversion.
+- A session runs one turn at a time. "Claude is working" means `startTurn`'s
+  check (an unsettled turn in `turnQueue`, or `foregroundWork` for the session);
+  don't write a narrower one. Anything that sends `session/update` must go
+  through the turn queue or be refused while the session is busy, or its output
+  lands inside another turn. Keep the session marked busy across awaited network
+  calls.
+- Don't branch on a local copy of state that Claude Code or a remote service
+  owns: it goes stale when the other side changes. Have a command set the state
+  the user asks for instead of toggling it.
+- A command or name the adapter adds must not shadow one that Claude Code or the
+  user's own commands and skills already provide.
+- New optional request fields and `_meta` keys must not reject requests that
+  were valid before.
+- If a workaround or new path is unavoidable (e.g. a Claude Code or SDK
+  limitation), say why in a short code comment and in the PR description.
+
+## Testing guidelines
+
+- Before adding a test, search `src/tests/` for existing tests of the same API
+  and scenario, and add to their file and `describe` block. Use the helpers in
+  `helpers.ts` and `session-doubles.ts` instead of copying setup.
+- Don't add cases that take the same code path. Tests that differ only in input
+  and expected output belong in one `it.each`. Don't repeat another test's
+  assertions; assert only what this test is about.
+- Reach a state the shortest way (e.g. set `session.tornDown = true`) instead of
+  driving a full flow with extra mocks, unless the flow is what you test.
+- Build test doubles from what the bundled Claude Code CLI really sends,
+  including fields like `origin` it echoes back and fields it omits. A double
+  simpler than the real message hides bugs. If unsure, check against the real
+  CLI (`npm run test:integration`).
+- Cover both ACP v1 and v2 when a change affects what a client receives
+  (updates, responses, replay). A change to internal logic only does not need
+  its tests duplicated per version.
+- For each behavior the docs or comments promise, including what is omitted or
+  rejected, have a test that would fail if it broke.

 ## Pull requests

--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,45 @@
 # Changelog

+## [0.101.0](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.100.0...v0.101.0) (2026-11-05)
+
+
+### Features
+
+* compact idle sessions before the prompt cache expires ([#1522](https://github.com/agentclientprotocol/claude-agent-acp/issues/1522)) ([a79d073](https://github.com/agentclientprotocol/claude-agent-acp/commit/a79d07324dc15808c94a889a3b60615cca5a9fbd)), closes [#1454](https://github.com/agentclientprotocol/claude-agent-acp/issues/1454) [#1518](https://github.com/agentclientprotocol/claude-agent-acp/issues/1518)
+* ship single-file executables built with bun ([#1524](https://github.com/agentclientprotocol/claude-agent-acp/issues/1524)) ([e3f0b6c](https://github.com/agentclientprotocol/claude-agent-acp/commit/e3f0b6c89c783939e6ca8c19c220c21b58263f46))
+* start sessions in Auto mode by default ([#1533](https://github.com/agentclientprotocol/claude-agent-acp/issues/1533)) ([7ea9eec](https://github.com/agentclientprotocol/claude-agent-acp/commit/7ea9eec8392a43191b25a5c3636c181cc7eb42f3))
+* stream the output of v2 background commands ([#1512](https://github.com/agentclientprotocol/claude-agent-acp/issues/1512)) ([53e3eec](https://github.com/agentclientprotocol/claude-agent-acp/commit/53e3eec0134209654f53c46f319aaac851b8fff0))
+
+
+### Bug Fixes
+
+* honor configured fallback for unavailable restored modes ([#1520](https://github.com/agentclientprotocol/claude-agent-acp/issues/1520)) ([8bbdea6](https://github.com/agentclientprotocol/claude-agent-acp/commit/8bbdea6cc62a7ae080cb73ff476ed28ad7574018))
+* update to @anthropic-ai/claude-agent-sdk 0.3.318 ([#1525](https://github.com/agentclientprotocol/claude-agent-acp/issues/1525)) ([1d4418f](https://github.com/agentclientprotocol/claude-agent-acp/commit/1d4418f80daf14c29cecc5b23286f52c7f0402ec))
+
+## [0.100.0](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.99.1...v0.100.0) (2026-11-02)
+
+
+### Features
+
+* list v2 background tool calls ([#1511](https://github.com/agentclientprotocol/claude-agent-acp/issues/1511)) ([4d79b9f](https://github.com/agentclientprotocol/claude-agent-acp/commit/4d79b9ffbce95c23928a5dd771d6c87476d37160))
+* report subagent working directories ([#1496](https://github.com/agentclientprotocol/claude-agent-acp/issues/1496)) ([eb78afa](https://github.com/agentclientprotocol/claude-agent-acp/commit/eb78afa8556b8fc4082495e48e3fd1762fb6a50f))
+* report v2 background work ([#1510](https://github.com/agentclientprotocol/claude-agent-acp/issues/1510)) ([5565259](https://github.com/agentclientprotocol/claude-agent-acp/commit/5565259771cb74e3a9bdbacfcbce43e061d81422))
+* report why Claude Code could not start a session ([#1508](https://github.com/agentclientprotocol/claude-agent-acp/issues/1508)) ([38cf656](https://github.com/agentclientprotocol/claude-agent-acp/commit/38cf656fc9d80fec2d1a16c472779803e2c802d2))
+
+
+### Bug Fixes
+
+* align session/cancel, session/close, and v2 setup with the ACP v2 spec ([#1494](https://github.com/agentclientprotocol/claude-agent-acp/issues/1494)) ([f50598a](https://github.com/agentclientprotocol/claude-agent-acp/commit/f50598a39c5dc3908d4b98a7213e01d63ea867d5))
+* forward v2 elicitation values and read dismissed v2 permission prompts as a refusal ([#1493](https://github.com/agentclientprotocol/claude-agent-acp/issues/1493)) ([3bc6711](https://github.com/agentclientprotocol/claude-agent-acp/commit/3bc671193c6456516fe05a0eaa53c17bdfb6a190))
+* keep native Windows paths in v2 git patches ([#1492](https://github.com/agentclientprotocol/claude-agent-acp/issues/1492)) ([c3428de](https://github.com/agentclientprotocol/claude-agent-acp/commit/c3428de1bf411c513b0703ddd56bb6c5fdff583c))
+* preserve live session settings across provider refreshes ([#1474](https://github.com/agentclientprotocol/claude-agent-acp/issues/1474)) ([e01a288](https://github.com/agentclientprotocol/claude-agent-acp/commit/e01a28838499dd6dd7c31e35708090b938e852c6))
+* reject unreadable skill manifests ([#1482](https://github.com/agentclientprotocol/claude-agent-acp/issues/1482)) ([99a6e76](https://github.com/agentclientprotocol/claude-agent-acp/commit/99a6e76158b9164e51bd62e3b89113beadea5ce2))
+* report the fresh context's usage when ExitPlanMode clears context ([#1484](https://github.com/agentclientprotocol/claude-agent-acp/issues/1484)) ([2fd46c8](https://github.com/agentclientprotocol/claude-agent-acp/commit/2fd46c866d4ff2939fe1b1245b15a536d6de7c0b))
+* update to @agentclientprotocol/sdk 2.2.0 ([#1491](https://github.com/agentclientprotocol/claude-agent-acp/issues/1491)) ([1d2b92f](https://github.com/agentclientprotocol/claude-agent-acp/commit/1d2b92feae5eeccde3ac738edca1f1d71250762e))
+* update to @agentclientprotocol/sdk 2.4.0 ([#1509](https://github.com/agentclientprotocol/claude-agent-acp/issues/1509)) ([720bbb3](https://github.com/agentclientprotocol/claude-agent-acp/commit/720bbb3e4c65874775a0bb9418799baf4b6e3680))
+* update to Claude Agent SDK 0.3.316 (Claude Code 2.1.316) ([#1507](https://github.com/agentclientprotocol/claude-agent-acp/issues/1507)) ([1d03064](https://github.com/agentclientprotocol/claude-agent-acp/commit/1d0306468b632c6a56b4fb076ad7a19f23d9e7b5))
+* validate session, prompt, config, and auth requests per the latest ACP spec ([#1495](https://github.com/agentclientprotocol/claude-agent-acp/issues/1495)) ([d2ef490](https://github.com/agentclientprotocol/claude-agent-acp/commit/d2ef490a318033049af00cb9164a39ac2dd1eb95))
+
 ## [0.99.1](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.99.0...v0.99.1) (2026-10-29)


--- a/README.md
+++ b/README.md
@@ -36,6 +36,23 @@ To try changes that have landed on `main` but are not released yet, install from
 npm install @agentclientprotocol/claude-agent-acp@preview
 ```

+### Standalone executables
+
+Each release attaches archives for Linux (glibc and musl), macOS and Windows, on
+x64 and arm64, to its [GitHub release](https://github.com/agentclientprotocol/claude-agent-acp/releases).
+They need no Node.js install. Each holds two files: `claude-agent-acp`, and the
+Claude CLI (`claude`) it runs. Keep them in the same directory; a symlink to
+`claude-agent-acp` elsewhere works. To use a Claude CLI you already have
+instead, set `CLAUDE_CODE_EXECUTABLE`. On Alpine, install `libgcc` and
+`libstdc++` first.
+
+To build one for your machine (needs [Bun](https://bun.sh)) and check it:
+
+```sh
+npm run build:binary
+npm run smoke:binary            # add `-- --full` to drive a real session; needs a Claude login
+```
+
 ### Subagent sessions

 A client that declares `clientCapabilities.subagents`, other than JetBrains AIR, gets each Agent or
@@ -48,6 +65,14 @@ Task subagent as its own child session, following the [subagents RFD](https://gi
  `end_turn` or `cancelled` when the SDK gives the reason. A failure is `idle` with the `error`
  stop reason and the SDK's error text as its `error`. The child keeps its session for every
  delegation to it.
+- A child that runs outside its parent's working directory, such as an Agent call with
+  `isolation: "worktree"`, gets its `cwd` on `subagent_update` before its first tool call. The
+  adapter takes it from the `cwd` of the child's own hooks: its SubagentStart hook runs before its
+  first model request. It sends `cwd: null` when the child is back in its parent's directory. A
+  child in its parent's directory gets no `cwd`, and no child gets `additionalDirectories`: Claude
+  Code gives a subagent the session's additional directories, so it inherits them. A replay
+  announces a child with the `cwd` that its transcript recorded, and clears it after the response
+  when that directory no longer exists.
 - Session messages replace the Agent or Task call that launches the child, which its parent is
  not shown:
  - The launch's prompt is a `session_message` in both transcripts: the parent's outgoing view and
--- a/docs/RELEASES.md
+++ b/docs/RELEASES.md
@@ -7,7 +7,9 @@ keeps a single release PR open, titled `chore(main): release X.Y.Z` and labelled
 `autorelease: pending`.

 Merging that PR is what releases. It tags `vX.Y.Z`, creates the GitHub release,
-publishes to npm, and dispatches a version update to the agent registry.
+publishes to npm, dispatches a version update to the agent registry, and
+attaches the [standalone executables](../README.md#standalone-executables) to
+the GitHub release. Previews get no executables.

 There is no manual release button, and versions are never typed in by hand: the
 version is an output of the commit history, not an input.
@@ -45,6 +47,9 @@ gh release view "v<version>"
 npm view "@agentclientprotocol/claude-agent-acp@<version>"
 ```

+The release should list 8 `claude-agent-acp-*` archives. They are attached a
+few minutes after the release is created, once every platform has built.
+
 ## Preview releases

 Every push to `main` that is not a release merge publishes a preview from the
@@ -203,6 +208,13 @@ npm versions are immutable. If the package already published and only the
 registry update failed, pass `-f publish_npm=false` so the run skips publishing
 and only re-dispatches the registry update.

+### The release has no executables
+
+`build-binaries` and `upload-binaries` don't gate npm, so a failed build only
+leaves the release without archives. Re-run the failed jobs of that publish run
+(`gh run rerun <run-id> --failed`); the upload uses `--clobber`, so archives
+already attached are replaced rather than duplicated.
+
 ### A preview published but the commit was not tagged

 Only the publish is irreversible, so re-run just the tag job:
--- a/docs/air-extensions.md
+++ b/docs/air-extensions.md
@@ -1569,7 +1569,7 @@ It is idempotent, and an unknown id also returns `{}`.
 `session/delete`:

 - a `sessionIndex` client: deletes every transcript of the session (empty ones too) and every `<sessionId>/` directory, also one left without a transcript by an earlier failed delete. Anything left behind fails the request. A session that runs here is closed first. As with the CLI, the session is deleted also when another Claude Code process has it open. An unknown session is `-32002`.
- an AIR client without `sessionIndex`: archives the session instead of deleting it (the title records of [Archive](#archive)), because AIR uses delete for "Done" and can reopen the session. A session that runs here is closed first. The list hides archived sessions from such a client too: those whose custom title, as the SDK list reports it, is archived. A session without a transcript fails with the error of the SDK delete, as before.
+- an AIR client without `sessionIndex`: archives the session instead of deleting it (the title records of [Archive](#archive)), because AIR uses delete for "Done" and can reopen the session. A session that runs here is closed first. The list hides archived sessions from such a client too: those whose custom title, as the SDK list reports it, is archived. A session without a transcript has nothing to archive, so the delete succeeds, as ACP asks of a session that does not exist.
  A `sessionIndex` client sees such a session as archived (`archived: true`), as AIR's native Claude path does.
 - any other client: the SDK delete. A session without a transcript (unknown, deleted before, or
  never prompted) succeeds, as ACP asks.
@@ -1679,14 +1679,14 @@ For AIR, both forms carry `_meta.jetbrains.air.contextCompaction`:
 }
 ```

-| Field        | Meaning                                                               |
-| ------------ | --------------------------------------------------------------------- |
-| `version`    | Must equal `1`.                                                       |
-| `trigger`    | `manual` or `automatic`.                                              |
-| `preTokens`  | The context size before the compaction.                               |
-| `postTokens` | The context size after the compaction.                                |
-| `durationMs` | The duration of the compaction.                                       |
-| `error`      | The error of a failed compaction. Only the tool call form carries it. |
+| Field        | Meaning                                                                                                  |
+| ------------ | -------------------------------------------------------------------------------------------------------- |
+| `version`    | Must equal `1`.                                                                                          |
+| `trigger`    | `manual`, `automatic`, or `idle`: the adapter compacted an idle session before its prompt cache expired. |
+| `preTokens`  | The context size before the compaction.                                                                  |
+| `postTokens` | The context size after the compaction.                                                                   |
+| `durationMs` | The duration of the compaction.                                                                          |
+| `error`      | The error of a failed compaction. Only the tool call form carries it.                                    |

 The standard `toolCallId` or `compactionId` and the `status` own the identity and the phase.
 The `compaction_update` form puts the error in the standard `error` field.
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,16 +1,16 @@
 {
  "name": "@agentclientprotocol/claude-agent-acp",
-  "version": "0.99.1",
+  "version": "0.101.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "@agentclientprotocol/claude-agent-acp",
-      "version": "0.99.1",
+      "version": "0.101.0",
      "license": "Apache-2.0",
      "dependencies": {
-        "@agentclientprotocol/sdk": "2.1.0",
-        "@anthropic-ai/claude-agent-sdk": "0.3.312",
+        "@agentclientprotocol/sdk": "2.4.0",
+        "@anthropic-ai/claude-agent-sdk": "0.3.318",
        "diff": "9.0.0",
        "zod": "4.6.7"
      },
@@ -18,29 +18,29 @@
        "claude-agent-acp": "dist/index.js"
      },
      "devDependencies": {
-        "@anthropic-ai/sdk": "1.3.0",
+        "@anthropic-ai/sdk": "1.4.0",
        "@eslint/js": "10.0.1",
        "@tsconfig/node22": "22.0.6",
-        "@types/node": "26.6.5",
+        "@types/node": "26.6.6",
        "@typescript-eslint/eslint-plugin": "8.72.1",
        "@typescript-eslint/parser": "8.72.1",
        "ajv": "8.20.0",
        "ajv-formats": "3.0.1",
-        "eslint": "10.13.0",
+        "eslint": "10.14.0",
        "eslint-config-prettier": "10.1.8",
-        "globals": "17.13.0",
+        "globals": "17.14.0",
        "prettier": "3.9.10",
        "typescript": "6.0.3",
-        "vitest": "5.0.5"
+        "vitest": "5.1.0"
      },
      "engines": {
        "node": ">=22"
      }
    },
    "node_modules/@agentclientprotocol/sdk": {
-      "version": "2.1.0",
-      "resolved": "https://registry.npmjs.org/@agentclientprotocol/sdk/-/sdk-2.1.0.tgz",
-      "integrity": "sha512-IuKjJmHLPzbmbg26eK9Jopd8AVxgLuu8fX114YzYAU6tLYclCo2DUzLL4vbCpYGr9mzvs2T0kigE3ZCueL06tg==",
+      "version": "2.4.0",
+      "resolved": "https://registry.npmjs.org/@agentclientprotocol/sdk/-/sdk-2.4.0.tgz",
+      "integrity": "sha512-7qJ8nnyj7WesC5ve185ioTpB2/svQoeGV4HA4nLEhgDUrcmBe54/08VcXc/oL4p14tDbxxECZzdYmUYQ+4l+Wg==",
      "license": "Apache-2.0",
      "peerDependencies": {
        "@modelcontextprotocol/server": "^2.4.0",
@@ -53,22 +53,22 @@
      }
    },
    "node_modules/@anthropic-ai/claude-agent-sdk": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk/-/claude-agent-sdk-0.3.312.tgz",
-      "integrity": "sha512-Ilj5Agx3ak/Z0UPZNLS7+CTnYMa+Ijf8+FKelh9MKGRwHVYyfvmJgL0fsmooI78SdkZwqjI5a4CwOAsJurdjJA==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk/-/claude-agent-sdk-0.3.318.tgz",
+      "integrity": "sha512-z5WHCUeW52SKQ3rnvI3zt8X5h2QQ5o3Cgg5xarO5Rimfe67f3pOJt2aOh00S8t/nRzqfs+8nCb9o1EoXe+yccA==",
      "license": "SEE LICENSE IN README.md",
      "engines": {
        "node": ">=18.14.0"
      },
      "optionalDependencies": {
-        "@anthropic-ai/claude-agent-sdk-darwin-arm64": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-darwin-x64": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-linux-arm64": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-linux-arm64-musl": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-linux-x64": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-linux-x64-musl": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-win32-arm64": "0.3.312",
-        "@anthropic-ai/claude-agent-sdk-win32-x64": "0.3.312"
+        "@anthropic-ai/claude-agent-sdk-darwin-arm64": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-darwin-x64": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-linux-arm64": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-linux-arm64-musl": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-linux-x64": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-linux-x64-musl": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-win32-arm64": "0.3.318",
+        "@anthropic-ai/claude-agent-sdk-win32-x64": "0.3.318"
      },
      "peerDependencies": {
        "@anthropic-ai/sdk": ">=0.93.0",
@@ -77,9 +77,9 @@
      }
    },
    "node_modules/@anthropic-ai/claude-agent-sdk-darwin-arm64": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-darwin-arm64/-/claude-agent-sdk-darwin-arm64-0.3.312.tgz",
-      "integrity": "sha512-AVmdMOuoeE3Y9f4wAIPcEAAS0OFaZw1L6l11YuyqfS0B/+DYxkWxS/ZYZ1NbUy57eaIW/vdEgz9Q5M99Pl6ZJw==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-darwin-arm64/-/claude-agent-sdk-darwin-arm64-0.3.318.tgz",
+      "integrity": "sha512-AWoXeDXzAMD3RaA21lWuHvCrKd8xmbTTmKjovninn4j07jheoVSMzFbCFjpp4kk5TdhT36JtWPkAxvjNMbcO8w==",
      "cpu": [
        "arm64"
      ],
@@ -90,9 +90,9 @@
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-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-darwin-x64/-/claude-agent-sdk-darwin-x64-0.3.312.tgz",
-      "integrity": "sha512-Dmxyil+GPzF1WENoFOi1Cx0roSdJA6HewGAfAFvsH5vYrzb6G0REGuoQQ0n3u8i8qFgtl1m/WSl4u5t+MdiHWA==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-darwin-x64/-/claude-agent-sdk-darwin-x64-0.3.318.tgz",
+      "integrity": "sha512-6CkZ5PCdebSY/LePp16sf/HYRtM6zVuxtn8qYICFS5KUZFsjccJJ9swVsOdHXNHi4SWZcSmIFTwoUbfFCzisRw==",
      "cpu": [
        "x64"
      ],
@@ -103,9 +103,9 @@
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    },
    "node_modules/@anthropic-ai/claude-agent-sdk-linux-arm64": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-arm64/-/claude-agent-sdk-linux-arm64-0.3.312.tgz",
-      "integrity": "sha512-jebsXksKh7g7u1x+RxjYQXM50TCN0e7GthebXa+n5IebF3pPqtmyWGVIiEEjvpajn3P6Zh8BWUVuufUpXn8ccA==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-arm64/-/claude-agent-sdk-linux-arm64-0.3.318.tgz",
+      "integrity": "sha512-mBm4su17aMitLBBCQj3bHdejyUDY6z/ormGih+HG24N689RSbdKECjGjkT87tDBIR/4jyoqmuSeHqM1DI8TJlg==",
      "cpu": [
        "arm64"
      ],
@@ -119,9 +119,9 @@
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    },
    "node_modules/@anthropic-ai/claude-agent-sdk-linux-arm64-musl": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-arm64-musl/-/claude-agent-sdk-linux-arm64-musl-0.3.312.tgz",
-      "integrity": "sha512-9GT0JzbfhODwsCO3MCg79wPH47qARCuKECcryeAJnVczplAlXSIiBw1+6UcqL5+0wSYFu6D/tvw/AiVy+PkHsg==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-arm64-musl/-/claude-agent-sdk-linux-arm64-musl-0.3.318.tgz",
+      "integrity": "sha512-l4LSYFOrvlYCrUImGfxMTQ0wg+T3s9CBhrBvPF/0oJGKZg+QnxHHU8jUVm9e9/xYmDRTtqFIrr4id/5AfH4XGw==",
      "cpu": [
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@@ -135,9 +135,9 @@
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    "node_modules/@anthropic-ai/claude-agent-sdk-linux-x64": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-x64/-/claude-agent-sdk-linux-x64-0.3.312.tgz",
-      "integrity": "sha512-UOsqza2uo5gqlX2OU72LhkQvIaNJKUQMJIi1poX2NtYqaWACqNo/TZPWfOBzxhyWmX8BLWaOlcuZGPLgcCJOTg==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-x64/-/claude-agent-sdk-linux-x64-0.3.318.tgz",
+      "integrity": "sha512-+mE+ueBD3oRFdaG16rd0h+LMjdeivGxL0pr/+FZK7JeLWVu+yPSw/f/X02b9oK36/DWykiFTu2G6HnJ9/+YO6w==",
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        "x64"
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@@ -151,9 +151,9 @@
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    "node_modules/@anthropic-ai/claude-agent-sdk-linux-x64-musl": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-x64-musl/-/claude-agent-sdk-linux-x64-musl-0.3.312.tgz",
-      "integrity": "sha512-zM+PB6qVybdwtlqElXQ4+wCwk2v/jjT3Xau4foydzy/g5pGRTuGT3PTcfDLeG0j9zF8IxLaCQ/+Bl9MABPQD8g==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-linux-x64-musl/-/claude-agent-sdk-linux-x64-musl-0.3.318.tgz",
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@@ -167,9 +167,9 @@
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    "node_modules/@anthropic-ai/claude-agent-sdk-win32-arm64": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-win32-arm64/-/claude-agent-sdk-win32-arm64-0.3.312.tgz",
-      "integrity": "sha512-Li9CyzsC2mzGmF1wtt/R59ChBLww6nc2dLn6tb+bgTDcd6kqvW44x5rIH+lRmBcpTNHR/8VO/k+GlmnkxqeaQQ==",
+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-win32-arm64/-/claude-agent-sdk-win32-arm64-0.3.318.tgz",
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@@ -180,9 +180,9 @@
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    "node_modules/@anthropic-ai/claude-agent-sdk-win32-x64": {
-      "version": "0.3.312",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-win32-x64/-/claude-agent-sdk-win32-x64-0.3.312.tgz",
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+      "version": "0.3.318",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/claude-agent-sdk-win32-x64/-/claude-agent-sdk-win32-x64-0.3.318.tgz",
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      "cpu": [
        "x64"
      ],
@@ -193,9 +193,9 @@
      ]
    },
    "node_modules/@anthropic-ai/sdk": {
-      "version": "1.3.0",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/sdk/-/sdk-1.3.0.tgz",
-      "integrity": "sha512-k7z9BlLLPxfZH+ov7dS6EnaN/wiZeV8YNT1LZfrpAHIy7oY7pHr4UzirF9f2OlHtFEnRBOX+AZQ91Y5fK+TPTw==",
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/sdk/-/sdk-1.4.0.tgz",
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      "license": "Apache-2.0",
      "dependencies": {
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@@ -363,9 +363,9 @@
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    "node_modules/@hono/node-server": {
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+      "resolved": "https://registry.npmjs.org/@hono/node-server/-/node-server-2.1.6.tgz",
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      "license": "MIT",
      "peer": true,
      "engines": {
@@ -544,9 +544,9 @@
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+      "resolved": "https://registry.npmjs.org/@oxc-project/types/-/types-0.156.0.tgz",
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      "dev": true,
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@@ -555,9 +555,9 @@
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+      "version": "1.2.16",
+      "resolved": "https://registry.npmjs.org/@rolldown/binding-android-arm-eabi/-/binding-android-arm-eabi-1.2.16.tgz",
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@@ -573,9 +573,9 @@
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@@ -591,9 +591,9 @@
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@@ -609,9 +609,9 @@
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@@ -627,9 +627,9 @@
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      "optionalDependencies": {
-        "@rolldown/binding-android-arm-eabi": "1.2.15",
-        "@rolldown/binding-android-arm64": "1.2.15",
-        "@rolldown/binding-darwin-arm64": "1.2.15",
-        "@rolldown/binding-darwin-x64": "1.2.15",
-        "@rolldown/binding-freebsd-x64": "1.2.15",
-        "@rolldown/binding-linux-arm-gnueabihf": "1.2.15",
-        "@rolldown/binding-linux-arm64-gnu": "1.2.15",
-        "@rolldown/binding-linux-arm64-musl": "1.2.15",
-        "@rolldown/binding-linux-ppc64-gnu": "1.2.15",
-        "@rolldown/binding-linux-s390x-gnu": "1.2.15",
-        "@rolldown/binding-linux-x64-gnu": "1.2.15",
-        "@rolldown/binding-linux-x64-musl": "1.2.15",
-        "@rolldown/binding-openharmony-arm64": "1.2.15",
-        "@rolldown/binding-win32-arm64-msvc": "1.2.15",
-        "@rolldown/binding-win32-x64-msvc": "1.2.15"
+        "@rolldown/binding-android-arm-eabi": "1.2.16",
+        "@rolldown/binding-android-arm64": "1.2.16",
+        "@rolldown/binding-darwin-arm64": "1.2.16",
+        "@rolldown/binding-darwin-x64": "1.2.16",
+        "@rolldown/binding-freebsd-x64": "1.2.16",
+        "@rolldown/binding-linux-arm-gnueabihf": "1.2.16",
+        "@rolldown/binding-linux-arm64-gnu": "1.2.16",
+        "@rolldown/binding-linux-arm64-musl": "1.2.16",
+        "@rolldown/binding-linux-ppc64-gnu": "1.2.16",
+        "@rolldown/binding-linux-s390x-gnu": "1.2.16",
+        "@rolldown/binding-linux-x64-gnu": "1.2.16",
+        "@rolldown/binding-linux-x64-musl": "1.2.16",
+        "@rolldown/binding-openharmony-arm64": "1.2.16",
+        "@rolldown/binding-win32-arm64-msvc": "1.2.16",
+        "@rolldown/binding-win32-x64-msvc": "1.2.16"
      }
    },
    "node_modules/router": {
@@ -3330,9 +3334,9 @@
      "peer": true
    },
    "node_modules/semver": {
-      "version": "7.8.5",
-      "resolved": "https://registry.npmjs.org/semver/-/semver-7.8.5.tgz",
-      "integrity": "sha512-Y7/KDsb8LjooZpwaqGyulO6DQlksgCncchHGk+sZIY4SBvUocMBEFH5Ur1fI4dV+Jvl0w6cjvucaIi40puRioA==",
+      "version": "7.8.6",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-7.8.6.tgz",
+      "integrity": "sha512-9lpSSU4Mly3mrtruwLs1eLK6+gzbzqeBFwRNjIjE+9LuDpWdYctrQlQ3ej1Ilgi7gknpsTRnPoLP8DpCHqHIJw==",
      "dev": true,
      "license": "ISC",
      "bin": {
@@ -3532,9 +3536,9 @@
      "license": "MIT"
    },
    "node_modules/tinybench": {
-      "version": "6.2.2",
-      "resolved": "https://registry.npmjs.org/tinybench/-/tinybench-6.2.2.tgz",
-      "integrity": "sha512-nIZ2N2dFpjBsg2hgitKu7mA+FvsIJuGJOwysRngmVRRmWgR/UyPjwJj8c/fT/dhm8EkHnF5EOogRf+0Z2qrimA==",
+      "version": "6.2.3",
+      "resolved": "https://registry.npmjs.org/tinybench/-/tinybench-6.2.3.tgz",
+      "integrity": "sha512-Al01C2JIBnO2CXCAPbpAl6sUiOZHeThGtHYNTa51JRw9PyWOCdr+9Ong05R4qg/Sk3+H645E8ov1h2c58ityNw==",
      "dev": true,
      "license": "MIT",
      "engines": {
@@ -3774,14 +3778,14 @@
      }
    },
    "node_modules/vitest": {
-      "version": "5.0.5",
-      "resolved": "https://registry.npmjs.org/vitest/-/vitest-5.0.5.tgz",
-      "integrity": "sha512-cPODOMF8YnkiiYtDdHo6n4wWmBrOBBbOIYH2d33M4l3CdNn72h+qMmO6uXffUN6A5AZFXNND/d+krS9mgkXRfg==",
+      "version": "5.1.0",
+      "resolved": "https://registry.npmjs.org/vitest/-/vitest-5.1.0.tgz",
+      "integrity": "sha512-MzmNFnrwa8v8lF1bLxw3UJ4EREwVOVb75VqJZmUDRjJ6EluK/x9th7qTbaeDk41WxE1GxWqmTXcdsfobfH5sOA==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
        "@types/chai": "^5.2.2",
-        "@vitest/mocker": "5.0.5",
+        "@vitest/mocker": "5.1.0",
        "chai": "^6.3.0",
        "es-module-lexer": "^2.3.2",
        "expect-type": "^1.4.0",
@@ -3807,12 +3811,12 @@
        "@edge-runtime/vm": "*",
        "@opentelemetry/api": "^1.9.0",
        "@types/node": "^22.0.0 || >=24.0.0",
-        "@vitest/browser-playwright": "5.0.5",
-        "@vitest/browser-preview": "5.0.5",
+        "@vitest/browser-playwright": "5.1.0",
+        "@vitest/browser-preview": "5.1.0",
        "@vitest/browser-webdriverio": "^5.0.0-beta.5 || >=5.0.0",
-        "@vitest/coverage-istanbul": "5.0.5",
-        "@vitest/coverage-v8": "5.0.5",
-        "@vitest/ui": "5.0.5",
+        "@vitest/coverage-istanbul": "5.1.0",
+        "@vitest/coverage-v8": "5.1.0",
+        "@vitest/ui": "5.1.0",
        "happy-dom": "*",
        "jsdom": "*",
        "vite": "^6.4.0 || ^7.0.0 || ^8.0.0"
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
  "publishConfig": {
    "access": "public"
  },
-  "version": "0.99.1",
+  "version": "0.101.0",
  "description": "An ACP-compatible coding agent powered by the Claude Agent SDK (TypeScript)",
  "main": "dist/lib.js",
  "types": "dist/lib.d.ts",
@@ -21,12 +21,15 @@
  "files": [
    "dist/",
    "!dist/tests/",
+    "!dist/binary-entry.*",
    "README.md",
    "LICENSE",
    "package.json"
  ],
  "scripts": {
    "build": "tsc",
+    "build:binary": "node scripts/build-binary.mjs",
+    "smoke:binary": "node scripts/smoke-binary.mjs",
    "start": "node dist/index.js",
    "dev": "npm run build && npm run start",
    "example:simple-client": "node --experimental-strip-types --disable-warning=ExperimentalWarning examples/simple-client.ts",
@@ -65,25 +68,25 @@
    "node": ">=22"
  },
  "dependencies": {
-    "@agentclientprotocol/sdk": "2.1.0",
-    "@anthropic-ai/claude-agent-sdk": "0.3.312",
+    "@agentclientprotocol/sdk": "2.4.0",
+    "@anthropic-ai/claude-agent-sdk": "0.3.318",
    "diff": "9.0.0",
    "zod": "4.6.7"
  },
  "devDependencies": {
-    "@anthropic-ai/sdk": "1.3.0",
+    "@anthropic-ai/sdk": "1.4.0",
    "@eslint/js": "10.0.1",
    "@tsconfig/node22": "22.0.6",
-    "@types/node": "26.6.5",
+    "@types/node": "26.6.6",
    "@typescript-eslint/eslint-plugin": "8.72.1",
    "@typescript-eslint/parser": "8.72.1",
    "ajv": "8.20.0",
    "ajv-formats": "3.0.1",
-    "eslint": "10.13.0",
+    "eslint": "10.14.0",
    "eslint-config-prettier": "10.1.8",
-    "globals": "17.13.0",
+    "globals": "17.14.0",
    "prettier": "3.9.10",
    "typescript": "6.0.3",
-    "vitest": "5.0.5"
+    "vitest": "5.1.0"
  }
 }
--- a/scripts/build-binary.mjs
+++ b/scripts/build-binary.mjs
@@ -0,0 +1,92 @@
+#!/usr/bin/env node
+// Builds an executable of the agent with `bun build --compile` and copies the
+// target platform's Claude CLI next to it. Both files go in the release
+// archive: the executable runs the CLI from its own directory.
+//
+//   node scripts/build-binary.mjs [--target bun-linux-x64-musl] [--outfile path]
+//
+// --target defaults to the host. Cross-compiling needs the target's SDK
+// platform package installed; the script prints the install command when it
+// is missing.
+
+import { spawnSync } from "node:child_process";
+import { chmodSync, copyFileSync, readFileSync } from "node:fs";
+import { createRequire } from "node:module";
+import { dirname, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { parseArgs } from "node:util";
+
+const repoRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+
+function hostTarget() {
+  const os = process.platform === "win32" ? "windows" : process.platform;
+  // Node linked against glibc reports its version; musl builds don't.
+  const musl =
+    process.platform === "linux" && !process.report.getReport().header.glibcVersionRuntime;
+  return `bun-${os}-${process.arch}${musl ? "-musl" : ""}`;
+}
+
+const { values } = parseArgs({
+  options: {
+    target: { type: "string", default: hostTarget() },
+    outfile: { type: "string" },
+  },
+});
+const target = values.target;
+
+// Bun targets look like `bun-<os>-<arch>` with optional `-musl`, `-baseline` or
+// `-modern` suffixes; the SDK names its packages `<platform>-<arch>[-musl]`.
+const match = /^bun-(linux|darwin|windows)-(x64|arm64|aarch64)(?:-.+)?$/.exec(target);
+if (!match) {
+  console.error(
+    `Unsupported target "${target}". Expected e.g. bun-linux-x64, bun-darwin-arm64, bun-windows-x64.`,
+  );
+  process.exit(1);
+}
+const [, os, rawArch] = match;
+const platform = os === "windows" ? "win32" : os;
+const arch = rawArch === "aarch64" ? "arm64" : rawArch;
+const musl = target.split("-").includes("musl");
+const exe = os === "windows" ? ".exe" : "";
+const cliPackage = `@anthropic-ai/claude-agent-sdk-${platform}-${arch}${musl ? "-musl" : ""}`;
+const cliSpecifier = `${cliPackage}/claude${exe}`;
+const outfile = resolve(values.outfile ?? join(repoRoot, "dist-bin", `claude-agent-acp${exe}`));
+
+// Resolve from the SDK, the way claudeCliPath() does at runtime, so a nested
+// install is checked rather than only a hoisted one.
+const sdkRequire = createRequire(
+  createRequire(join(repoRoot, "package.json")).resolve("@anthropic-ai/claude-agent-sdk"),
+);
+let cliPath;
+try {
+  cliPath = sdkRequire.resolve(cliSpecifier);
+} catch {
+  const sdkVersion = JSON.parse(
+    readFileSync(
+      join(dirname(sdkRequire.resolve("@anthropic-ai/claude-agent-sdk")), "package.json"),
+      "utf8",
+    ),
+  ).version;
+  console.error(
+    `${cliSpecifier} is not installed. npm only installs the host's platform package; for ${target} run:\n\n` +
+      `  npm install --no-save --force ${cliPackage}@${sdkVersion}\n`,
+  );
+  process.exit(1);
+}
+
+const bun = spawnSync(
+  "bun",
+  ["build", "src/binary-entry.ts", "--compile", "--target", target, "--outfile", outfile],
+  { cwd: repoRoot, stdio: "inherit", shell: process.platform === "win32" },
+);
+if (bun.error) {
+  console.error(`Could not run bun: ${bun.error.message}. Install it from https://bun.sh.`);
+  process.exit(1);
+}
+if (bun.status !== 0) process.exit(bun.status ?? 1);
+
+// The executable runs the CLI from its own directory (src/binary-entry.ts).
+const cliOutfile = join(dirname(outfile), `claude${exe}`);
+copyFileSync(cliPath, cliOutfile);
+chmodSync(cliOutfile, 0o755);
+console.log(`Copied ${cliSpecifier} to ${cliOutfile}`);
--- a/scripts/smoke-binary.mjs
+++ b/scripts/smoke-binary.mjs
@@ -0,0 +1,470 @@
+#!/usr/bin/env node
+// Smoke-tests a built agent over ACP. Defaults to the executable from
+// scripts/build-binary.mjs, with `claude` next to it. Pass another command
+// after `--` to compare, e.g.
+// `node scripts/smoke-binary.mjs --full -- node "$PWD/dist/index.js"` (the full
+// run starts the agent in a scratch directory, so paths must be absolute).
+//
+//   node scripts/smoke-binary.mjs            # no login needed
+//   node scripts/smoke-binary.mjs --full     # talks to the model; needs a logged-in Claude
+//
+// SMOKE_DEBUG=1 prints every tool call the full run saw.
+//
+// The basic run checks `--version`, `--cli --version`, `initialize` (v1 and
+// v2) and the `terminal-auth` login command. The
+// full run also has Claude use Bash, Read (text and image), Edit and a
+// subagent in a scratch directory, then cancels a turn, lists the session,
+// loads it in a fresh agent process, and forks and deletes it.
+//
+// Claude Code's native builds have no Grep or Glob tool: its Bash shell wraps
+// `grep` and `find` in functions that run the ugrep and bfs built into the
+// Claude binary at `$CLAUDE_CODE_EXECPATH`. The full run checks that those
+// run, since they are the helpers a packaged build could fail to reach.
+
+import { spawn, spawnSync } from "node:child_process";
+import {
+  copyFileSync,
+  mkdirSync,
+  mkdtempSync,
+  readFileSync,
+  rmSync,
+  symlinkSync,
+  writeFileSync,
+} from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join, resolve } from "node:path";
+import readline from "node:readline";
+import { fileURLToPath } from "node:url";
+import { parseArgs } from "node:util";
+import { deflateSync } from "node:zlib";
+
+const repoRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const { values, positionals } = parseArgs({
+  options: { full: { type: "boolean", default: false } },
+  allowPositionals: true,
+});
+const exe = process.platform === "win32" ? ".exe" : "";
+const [command, ...commandArgs] =
+  positionals.length > 0 ? positionals : [join(repoRoot, "dist-bin", `claude-agent-acp${exe}`)];
+
+let failures = 0;
+function check(ok, label, detail) {
+  console.log(
+    `${ok ? "ok  " : "FAIL"} ${label}${!ok && detail !== undefined ? `: ${detail}` : ""}`,
+  );
+  if (!ok) failures++;
+  return ok;
+}
+
+// ---------------------------------------------------------------- basic
+
+function runSync(args, [cmd, ...cmdArgs] = [command, ...commandArgs]) {
+  const result = spawnSync(cmd, [...cmdArgs, ...args], {
+    encoding: "utf8",
+    timeout: 60_000,
+  });
+  return { stdout: (result.stdout ?? "").trim(), error: result.error ?? result.stderr };
+}
+
+const version = JSON.parse(readFileSync(join(repoRoot, "package.json"), "utf8")).version;
+const own = runSync(["--version"]);
+check(own.stdout === version, `--version prints ${version}`, own.stdout || own.error);
+const cli = runSync(["--cli", "--version"]);
+check(
+  /\(Claude Code\)$/.test(cli.stdout),
+  "--cli --version runs the bundled Claude CLI",
+  cli.stdout || cli.error,
+);
+
+// The release archive's layout: the executable finds `claude` in the directory
+// of its real path. Only for the default executable; a `--` command has no
+// such layout.
+if (positionals.length === 0) {
+  const scratch = mkdtempSync(join(tmpdir(), "acp-layout-"));
+  try {
+    if (process.platform !== "win32") {
+      const link = join(scratch, "claude-agent-acp");
+      symlinkSync(command, link);
+      const linked = runSync(["--cli", "--version"], [link]);
+      check(
+        /\(Claude Code\)$/.test(linked.stdout),
+        "a symlink to the executable finds the bundled CLI",
+        linked.stdout || linked.error,
+      );
+      rmSync(link);
+    }
+    const alone = join(scratch, `claude-agent-acp${exe}`);
+    copyFileSync(command, alone);
+    const missing = runSync(["--cli", "--version"], [alone]);
+    check(
+      String(missing.error).includes("The Claude CLI is missing"),
+      "without claude next to it, says the CLI is missing",
+      missing.stdout || missing.error,
+    );
+  } finally {
+    rmSync(scratch, { recursive: true, force: true });
+  }
+}
+
+/** Starts the agent and speaks newline-delimited JSON-RPC to it. */
+function startAgent(cwd, onNotification) {
+  const child = spawn(command, commandArgs, { cwd, stdio: ["pipe", "pipe", "pipe"] });
+  const stderr = [];
+  child.stderr.on("data", (chunk) => stderr.push(chunk));
+  let nextId = 0;
+  const pending = new Map();
+  const write = (message) =>
+    child.stdin.write(JSON.stringify({ jsonrpc: "2.0", ...message }) + "\n");
+  readline.createInterface({ input: child.stdout }).on("line", (line) => {
+    let message;
+    try {
+      message = JSON.parse(line);
+    } catch {
+      check(false, "stdout carries only JSON-RPC", line.slice(0, 200));
+      return;
+    }
+    if (message.method === undefined && pending.has(message.id)) {
+      pending.get(message.id)(message);
+      pending.delete(message.id);
+    } else if (message.method === "session/request_permission") {
+      const allow =
+        message.params.options.find((o) => o.kind === "allow_once") ?? message.params.options[0];
+      write({
+        id: message.id,
+        result: { outcome: { outcome: "selected", optionId: allow.optionId } },
+      });
+    } else if (message.id !== undefined && message.method !== undefined) {
+      write({
+        id: message.id,
+        error: { code: -32601, message: `smoke client does not handle ${message.method}` },
+      });
+    } else {
+      onNotification?.(message);
+    }
+  });
+  const exited = new Promise((resolve) => child.on("exit", resolve));
+  // Answer anything still pending if the agent dies, instead of hanging.
+  let exitError;
+  exited.then((code) => {
+    exitError = { message: `agent exited with ${code}: ${Buffer.concat(stderr)}` };
+    for (const resolve of pending.values()) resolve({ error: exitError });
+    pending.clear();
+  });
+  return {
+    request(method, params) {
+      const id = ++nextId;
+      return new Promise((resolve) => {
+        if (exitError) return resolve({ error: exitError });
+        pending.set(id, resolve);
+        write({ id, method, params });
+      });
+    },
+    notify: (method, params) => write({ method, params }),
+    async stop() {
+      child.stdin.end();
+      const code = await Promise.race([
+        exited,
+        new Promise((r) => setTimeout(() => r("timeout"), 10_000)),
+      ]);
+      if (code === "timeout") child.kill();
+      return { code, stderr: Buffer.concat(stderr).toString() };
+    },
+  };
+}
+
+const initializeParams = { protocolVersion: 1, clientCapabilities: {} };
+{
+  const agent = startAgent(process.cwd());
+  const init = await agent.request("initialize", initializeParams);
+  check(
+    init.result?.agentInfo?.version === version,
+    "initialize answers",
+    JSON.stringify(init.error),
+  );
+  const { code } = await agent.stop();
+  check(code === 0, "exits 0 when stdin closes", code);
+}
+{
+  // The `terminal-auth` login command reruns the agent; run it with
+  // `--version` in place of `auth login --console` instead of logging in.
+  // `--version` wins over a stray argument, so also check that no path inside
+  // a compiled executable leaked into the arguments.
+  const agent = startAgent(process.cwd());
+  const init = await agent.request("initialize", {
+    protocolVersion: 1,
+    clientCapabilities: { _meta: { "terminal-auth": true } },
+  });
+  await agent.stop();
+  const login = init.result?.authMethods?.find((m) => m.id === "console-login")?._meta?.[
+    "terminal-auth"
+  ];
+  const cliArgs = login?.args?.slice(0, login.args.indexOf("--cli") + 1);
+  const rerun = login
+    ? runSync([...cliArgs, "--version"], [login.command])
+    : { stdout: "", error: "no terminal-auth console-login method" };
+  check(
+    /\(Claude Code\)$/.test(rerun.stdout) &&
+      !login.args.some((arg) => arg.includes("$bunfs") || arg.includes("~BUN")),
+    "the terminal-auth login command reruns the agent",
+    `${JSON.stringify(login)} -> ${rerun.stdout || rerun.error}`,
+  );
+}
+{
+  const agent = startAgent(process.cwd());
+  const init = await agent.request("initialize", {
+    protocolVersion: 2,
+    info: { name: "smoke-binary", version },
+    capabilities: {},
+  });
+  check(
+    init.result?.protocolVersion === 2,
+    "initialize answers ACP v2",
+    JSON.stringify(init.error),
+  );
+  await agent.stop();
+}
+
+// ---------------------------------------------------------------- full
+
+if (values.full) {
+  const work = mkdtempSync(join(tmpdir(), "acp-smoke-"));
+  try {
+    await fullSmoke(work);
+  } finally {
+    rmSync(work, { recursive: true, force: true });
+  }
+}
+
+/** A solid red 16x16 PNG, so the model has something to name. */
+function redPng() {
+  const crcTable = Array.from({ length: 256 }, (_, n) => {
+    let c = n;
+    for (let k = 0; k < 8; k++) c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
+    return c >>> 0;
+  });
+  const crc = (buf) => {
+    let c = 0xffffffff;
+    for (const byte of buf) c = crcTable[(c ^ byte) & 0xff] ^ (c >>> 8);
+    return (c ^ 0xffffffff) >>> 0;
+  };
+  const chunk = (type, data) => {
+    const body = Buffer.concat([Buffer.from(type), data]);
+    const out = Buffer.alloc(body.length + 8);
+    out.writeUInt32BE(data.length, 0);
+    body.copy(out, 4);
+    out.writeUInt32BE(crc(body), body.length + 4);
+    return out;
+  };
+  const size = 16;
+  const header = Buffer.alloc(13);
+  header.writeUInt32BE(size, 0);
+  header.writeUInt32BE(size, 4);
+  header[8] = 8; // bit depth
+  header[9] = 2; // RGB
+  const row = Buffer.concat([Buffer.from([0]), Buffer.alloc(size * 3, Buffer.from([255, 0, 0]))]);
+  return Buffer.concat([
+    Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]),
+    chunk("IHDR", header),
+    chunk("IDAT", deflateSync(Buffer.concat(Array(size).fill(row)))),
+    chunk("IEND", Buffer.alloc(0)),
+  ]);
+}
+
+/** Writes its results to files so the checks don't depend on the model's reply. */
+function searchCommand(token) {
+  return [
+    `grep -rl "${token}" . > grep.out`,
+    'find . -name "*.md" > find.out',
+    '{ echo "$CLAUDE_CODE_EXECPATH"; grep --version | head -1; find --version | head -1; } > tools.out',
+  ].join("; ");
+}
+
+function searchResults(work) {
+  const read = (name) => {
+    try {
+      return readFileSync(join(work, name), "utf8");
+    } catch (error) {
+      return String(error);
+    }
+  };
+  const [execPath = "", grepVersion = "", findVersion = ""] = read("tools.out").split("\n");
+  return { grep: read("grep.out"), find: read("find.out"), execPath, grepVersion, findVersion };
+}
+
+async function fullSmoke(work) {
+  const token = `SMOKE_TOKEN_${process.pid}`;
+  mkdirSync(join(work, "notes"));
+  mkdirSync(join(work, "src"));
+  writeFileSync(join(work, "notes", "alpha.md"), `# Alpha\n\nThe token is ${token}.\n`);
+  writeFileSync(join(work, "notes", "beta.md"), "# Beta\n\nNothing here.\n");
+  writeFileSync(join(work, "src", "gamma.ts"), `export const value = "${token}";\n`);
+  writeFileSync(join(work, "pixel.png"), redPng());
+
+  const toolCalls = new Map();
+  let text = "";
+  const onNotification = (message) => {
+    if (message.method !== "session/update") return;
+    const update = message.params.update;
+    if (update.sessionUpdate === "agent_message_chunk" && update.content.type === "text") {
+      text += update.content.text;
+    } else if (
+      update.sessionUpdate === "tool_call" ||
+      update.sessionUpdate === "tool_call_update"
+    ) {
+      const call = toolCalls.get(update.toolCallId) ?? {};
+      toolCalls.set(update.toolCallId, {
+        ...call,
+        name: update._meta?.claudeCode?.toolName ?? call.name,
+        status: update.status ?? call.status,
+        title: update.title ?? call.title,
+      });
+    }
+  };
+
+  const agent = startAgent(work, onNotification);
+  await agent.request("initialize", initializeParams);
+  const created = await agent.request("session/new", { cwd: work, mcpServers: [] });
+  if (!check(created.result?.sessionId, "session/new", JSON.stringify(created.error))) {
+    console.error((await agent.stop()).stderr);
+    return;
+  }
+  const sessionId = created.result.sessionId;
+
+  const started = Date.now();
+  const prompt = await agent.request("session/prompt", {
+    sessionId,
+    prompt: [
+      {
+        type: "text",
+        text: [
+          "This is an automated smoke test of your tools. Do each step with the named tool, in order, one tool call per step:",
+          `1. Bash: run exactly \`${searchCommand(token)}\``,
+          "2. Read: read notes/alpha.md.",
+          "3. Read: read pixel.png and note its color.",
+          `4. Edit: in notes/alpha.md replace "${token}" with "EDITED".`,
+          "5. Bash: run `cat notes/alpha.md`.",
+          '6. Agent: launch a subagent (subagent_type "Explore") that counts the .ts files under src/ and reports the number.',
+          "Then reply with one line: SMOKE-DONE color=<the color of pixel.png> tsfiles=<the subagent's count>.",
+        ].join("\n"),
+      },
+    ],
+  });
+  check(
+    prompt.result?.stopReason === "end_turn",
+    "prompt ends with end_turn",
+    JSON.stringify(prompt.result ?? prompt.error),
+  );
+  console.log(`     (turn took ${Math.round((Date.now() - started) / 1000)}s)`);
+
+  const calls = [...toolCalls.values()];
+  if (process.env.SMOKE_DEBUG) console.log(JSON.stringify(calls, null, 1));
+  const searched = searchResults(work);
+  check(
+    searched.grep.includes("alpha.md") && searched.grep.includes("gamma.ts"),
+    "grep found the token",
+    searched.grep,
+  );
+  check(
+    searched.find.includes("alpha.md") && searched.find.includes("beta.md"),
+    "find listed the .md files",
+    searched.find,
+  );
+  check(
+    /^ugrep /.test(searched.grepVersion),
+    "grep ran Claude's embedded ugrep",
+    searched.grepVersion,
+  );
+  check(/^bfs /.test(searched.findVersion), "find ran Claude's embedded bfs", searched.findVersion);
+  console.log(`     (CLAUDE_CODE_EXECPATH=${searched.execPath})`);
+  for (const name of ["Read", "Edit", "Bash"]) {
+    const used = calls.filter((c) => c.name === name);
+    check(
+      used.length > 0 && used.every((c) => c.status === "completed"),
+      `${name} ran and completed`,
+      JSON.stringify(used),
+    );
+  }
+  const subagent = calls.filter((c) => c.name === "Agent" || c.name === "Task");
+  check(
+    subagent.some((c) => c.status === "completed"),
+    "subagent ran and completed",
+    JSON.stringify(subagent),
+  );
+  const failed = calls.filter((c) => c.status === "failed");
+  check(failed.length === 0, "no tool call failed", JSON.stringify(failed));
+  check(
+    readFileSync(join(work, "notes", "alpha.md"), "utf8").includes("EDITED"),
+    "Edit changed the file on disk",
+  );
+  check(
+    /SMOKE-DONE/.test(text) && /color=\W*red/i.test(text),
+    "image read as red",
+    text.slice(-300),
+  );
+  check(/tsfiles=\W*1\b/.test(text), "subagent counted 1 .ts file", text.slice(-300));
+
+  // A cancel interrupts a running Bash command and ends the turn as cancelled.
+  const cancelled = agent.request("session/prompt", {
+    sessionId,
+    prompt: [
+      { type: "text", text: "Use the Bash tool to run `sleep 60`. Do not run anything else." },
+    ],
+  });
+  const deadline = Date.now() + 60_000;
+  const bashRunning = () =>
+    [...toolCalls.values()].some((c) => c.name === "Bash" && c.status !== "completed");
+  while (!bashRunning() && Date.now() < deadline) {
+    await new Promise((r) => setTimeout(r, 200));
+  }
+  agent.notify("session/cancel", { sessionId });
+  const cancelResult = await cancelled;
+  check(
+    cancelResult.result?.stopReason === "cancelled",
+    "session/cancel ends the turn as cancelled",
+    JSON.stringify(cancelResult.result ?? cancelResult.error),
+  );
+
+  const listed = await agent.request("session/list", { cwd: work });
+  check(
+    listed.result?.sessions?.some((s) => s.sessionId === sessionId),
+    "session/list finds the session",
+    JSON.stringify(listed.result ?? listed.error),
+  );
+  const { code, stderr } = await agent.stop();
+  check(code === 0, "exits 0 when stdin closes", code);
+  if (failures > 0) console.error(stderr);
+
+  // A fresh process, so the replay comes from the transcript on disk.
+  let replayed = "";
+  const reloaded = startAgent(work, (message) => {
+    const update = message.params?.update;
+    if (update?.sessionUpdate === "user_message_chunk" && update.content.type === "text")
+      replayed += update.content.text;
+  });
+  await reloaded.request("initialize", initializeParams);
+  const loaded = await reloaded.request("session/load", { sessionId, cwd: work, mcpServers: [] });
+  check(!loaded.error, "session/load in a new process", JSON.stringify(loaded.error));
+  check(replayed.includes(token), "session/load replays the first prompt", replayed.slice(0, 200));
+
+  // Fork and delete go through the SDK's transcript helpers, not the CLI.
+  const forked = await reloaded.request("session/fork", { sessionId, cwd: work, mcpServers: [] });
+  const forkId = forked.result?.sessionId;
+  check(
+    forkId && forkId !== sessionId,
+    "session/fork",
+    JSON.stringify(forked.result ?? forked.error),
+  );
+  if (forkId) {
+    const deleted = await reloaded.request("session/delete", { sessionId: forkId });
+    const after = await reloaded.request("session/list", { cwd: work });
+    check(
+      !deleted.error && !after.result?.sessions?.some((s) => s.sessionId === forkId),
+      "session/delete removes the fork",
+      JSON.stringify(deleted.error ?? after.result),
+    );
+  }
+  await reloaded.stop();
+}
+
+console.log(failures === 0 ? "\nsmoke test passed" : `\n${failures} check(s) failed`);
+process.exit(failures === 0 ? 0 : 1);
--- a/src/acp-agent.ts
+++ b/src/acp-agent.ts
--- a/src/agent-command.ts
+++ b/src/agent-command.ts
@@ -0,0 +1,19 @@
+/**
+ * The command that starts this agent again with the flags it was started with,
+ * for a client to run in a terminal (e.g. `terminal-auth` login).
+ *
+ * Under Node, `process.argv` is `[node, script, ...flags]`, so the command is
+ * `node script ...flags`. In a `bun build --compile` executable it is
+ * `["bun", "/$bunfs/root/<name>", ...flags]` (`B:\~BUN\root\<name>` on
+ * Windows): `process.execPath` is the executable itself and `argv[1]` names a
+ * file inside it, which must not be passed back as an argument.
+ */
+export function agentCommand(argv: readonly string[] = process.argv): {
+  command: string;
+  args: string[];
+} {
+  const [, script, ...flags] = argv;
+  if (script === undefined) return { command: process.execPath, args: [] };
+  const compiled = script.includes("$bunfs") || script.includes("~BUN");
+  return { command: process.execPath, args: compiled ? flags : [script, ...flags] };
+}
--- a/src/async-tasks.ts
+++ b/src/async-tasks.ts
@@ -863,18 +863,29 @@ function recordPublished(task: AsyncTask, fields: Record<string, unknown>): void
 * Recovers a background Bash task from the structured `backgroundTaskId` of
 * its tool result. The text of a tool result never gives a task id: a
 * foreground command can print any text.
+ *
+ * Claude Code sends no `tool_use_result` with a subagent's tool results. For
+ * those, `startedTaskOf` gives the background `local_bash` task whose
+ * `task_started` named the Bash call, which comes before the result.
 */
 export function backgroundBashTaskFromToolResult(
  content: unknown,
  toolUseResult: unknown,
  toolUses: Record<string, { name: string; input: unknown }>,
+  startedTaskOf?: (toolUseId: string) => string | undefined,
 ): (AsyncTaskStarted & { taskId: string; toolCallId: string }) | undefined {
  if (!Array.isArray(content)) return undefined;
  const toolResults = content.flatMap(toolResultBlock);
  const bashResults = toolResults.filter((result) => toolUses[result.toolUseId]?.name === "Bash");
  if (bashResults.length === 0) return undefined;

-  const backgroundResults = structuredBackgroundResults(toolUseResult, toolUses);
+  let backgroundResults = structuredBackgroundResults(toolUseResult, toolUses);
+  if (backgroundResults.length === 0 && startedTaskOf) {
+    backgroundResults = bashResults.flatMap((result) => {
+      const taskId = result.isError ? undefined : startedTaskOf(result.toolUseId);
+      return taskId ? [{ taskId, toolUseId: result.toolUseId }] : [];
+    });
+  }
  const distinctTaskIds = new Set(backgroundResults.map((result) => result.taskId));
  if (distinctTaskIds.size !== 1) return undefined;
  const taskId = [...distinctTaskIds][0];
--- a/src/background-output.ts
+++ b/src/background-output.ts
@@ -0,0 +1,131 @@
+/**
+ * The output of a command that went to the background, read from the file
+ * that Claude Code writes it to. Claude Code streams no output of such a
+ * command, so its display terminal would show only the placeholder of the
+ * Bash result ("Command running in background with ID …") until the command
+ * exits. ACP v2 asks an Agent to keep a listed terminal's output current
+ * whenever it can read it (the v2 prompt lifecycle, "Background work").
+ *
+ * The file is polled: watching a file is not reliable on every platform, and
+ * a missing file only means that nothing was written yet.
+ */
+import { open } from "node:fs/promises";
+import { StringDecoder } from "node:string_decoder";
+
+/** How often a running command's output file is read. */
+export const BACKGROUND_OUTPUT_POLL_MS = 500;
+
+/** The most bytes one read takes, so a burst of output does not block the loop. */
+export const BACKGROUND_OUTPUT_READ_BYTES = 256 * 1024;
+
+/**
+ * The most unread bytes that are still sent. A command that writes faster
+ * than the polls read falls behind. Past this, the reads skip to the file's
+ * last bytes, as a snapshot: a terminal shows the latest output, and a
+ * client keeps a bounded amount of it anyway.
+ */
+export const BACKGROUND_OUTPUT_MAX_BACKLOG_BYTES = 1024 * 1024;
+
+/**
+ * Text that the file adds. A snapshot replaces the terminal's output so far:
+ * the first one replaces the placeholder of the Bash result, and a later one
+ * follows a skip or a file that shrank. Other text appends to it.
+ */
+export type BackgroundOutput = { text: string; replaces: boolean };
+
+/**
+ * Follows the output file `path` of one background command and hands each
+ * piece of new text to `publish`, in order. Reads never overlap. A read that
+ * fails, for example because the file does not exist yet, is tried again at
+ * the next poll. `publish` must not reject: the next read waits for it.
+ */
+export class BackgroundOutputTail {
+  private offset = 0;
+  private decoder = new StringDecoder("utf8");
+  /** Whether the next text replaces the terminal's output. */
+  private replaces = true;
+  private stopped = false;
+  private reading: Promise<void> = Promise.resolve();
+  private readonly timer: ReturnType<typeof setInterval>;
+
+  constructor(
+    private readonly path: string,
+    private readonly publish: (output: BackgroundOutput) => Promise<void>,
+  ) {
+    this.timer = setInterval(() => void this.read(false), BACKGROUND_OUTPUT_POLL_MS);
+    // A command that runs on must not keep the agent process alive.
+    this.timer.unref();
+  }
+
+  /**
+   * Reads the rest of the file and stops. The command ended, so what the file
+   * holds is its whole output, and it goes out before the terminal's exit.
+   */
+  async finish(): Promise<void> {
+    clearInterval(this.timer);
+    await this.read(true);
+    this.stopped = true;
+  }
+
+  /** Stops without reading more: the session ended. */
+  stop(): void {
+    clearInterval(this.timer);
+    this.stopped = true;
+  }
+
+  /**
+   * Reads what the file adds, one read of at most
+   * {@link BACKGROUND_OUTPUT_READ_BYTES} at a time, and publishes each read's
+   * text before the next. `toEnd` reads until the end of the file, and ends a
+   * character that the command cut off with a replacement character.
+   */
+  private read(toEnd: boolean): Promise<void> {
+    this.reading = this.reading.then(async () => {
+      if (this.stopped) return;
+      let file;
+      try {
+        file = await open(this.path, "r");
+      } catch {
+        // Nothing written yet, or the file is gone: try again at the next
+        // poll. At the end, the terminal keeps the output it has.
+        return;
+      }
+      try {
+        const { size } = await file.stat();
+        // A file that shrank is a new one: its output starts over. Past the
+        // backlog, the reads skip to the file's last bytes.
+        const start = size < this.offset ? 0 : this.offset;
+        const skipTo = Math.max(start, size - BACKGROUND_OUTPUT_MAX_BACKLOG_BYTES);
+        if (skipTo !== this.offset) {
+          this.offset = skipTo;
+          this.decoder = new StringDecoder("utf8");
+          this.replaces = true;
+        }
+        const buffer = Buffer.alloc(BACKGROUND_OUTPUT_READ_BYTES);
+        let bytesRead: number;
+        do {
+          ({ bytesRead } = await file.read(buffer, 0, buffer.length, this.offset));
+          this.offset += bytesRead;
+          const text = this.decoder.write(buffer.subarray(0, bytesRead));
+          if (text !== "") await this.send(text);
+        } while (toEnd && bytesRead > 0);
+        if (toEnd) {
+          const rest = this.decoder.end();
+          // A command that wrote nothing still replaces the placeholder.
+          if (rest !== "" || this.replaces) await this.send(rest);
+        }
+      } catch {
+        // The read failed: try again at the next poll.
+      } finally {
+        await file.close();
+      }
+    });
+    return this.reading;
+  }
+
+  private async send(text: string): Promise<void> {
+    const replaces = this.replaces;
+    this.replaces = false;
+    await this.publish({ text, replaces });
+  }
+}
--- a/src/background-work.ts
+++ b/src/background-work.ts
@@ -0,0 +1,629 @@
+/**
+ * The background work of a session: the work that Claude Code keeps running
+ * independently of the session's foreground work, which ACP v2 lists on every
+ * `state_update` of the session as `background` (the v2 prompt lifecycle,
+ * "Background work").
+ *
+ * The lists are built from Claude Code's live background task set
+ * (`background_tasks_changed`). Claude Code marks `ambient` its own
+ * housekeeping and every live-update watcher; those are left out, except a
+ * task that a tool call started, such as a `Monitor` call's. The root session and each
+ * announced subagent session (the subagents RFD form) has its own list. Each
+ * task is listed once, in the list of the session that runs it:
+ *
+ * - A command that went to the background: its display terminal, from the
+ *   Bash tool result until its task ends (`Session.backgroundTerminals`).
+ * - A detached subagent: its child session, in its parent's list, while it
+ *   works, and while it is idle with background work of its own.
+ * - A task that a tool call started, such as a `Monitor`, a `Workflow` or a
+ *   backgrounded MCP call: that tool call, kept `in_progress` (or `paused`)
+ *   from its tool result until its task ends (`Session.backgroundToolCalls`).
+ * - Any other task, once its `task_started` came and the tool call that
+ *   started it, if any, returned: a `_claude/task` item with the task's id
+ *   and description. For example, a task whose tool call ended before the
+ *   task joined the level.
+ *
+ * Only a session whose interrupt spares background tasks reports its lists
+ * (`Session.reportsBackground`): `session/cancel` must leave listed work
+ * running.
+ */
+import { RequestError } from "@agentclientprotocol/sdk/unstable";
+import type { AcpSessionNotification } from "./acp-subagents.js";
+import type { NativeSubagent } from "./native-subagents.js";
+import { type AcpToolCallRenderer, V2_CANCELLED, V2_PAUSED } from "./tool-calls/renderer.js";
+import { type BackgroundOutput, BackgroundOutputTail } from "./background-output.js";
+
+/** An item of a `background` list. */
+export type BackgroundItem =
+  | { type: "terminal"; terminalId: string }
+  | { type: "tool_call"; toolCallId: string }
+  | { type: "subagent"; sessionId: string }
+  | { type: "_claude/task"; taskId: string; description: string };
+
+/** The display terminal of a command that went to the background (see `Session.backgroundTerminals`). */
+export interface BackgroundTerminal {
+  /** The Bash tool call, whose id names the terminal. */
+  toolCallId: string;
+  /** The subagent tool call that ran the command, if any. */
+  parentToolUseId?: string;
+  /** The file that Claude Code writes the command's output to, from the Bash result. */
+  outputFilePath?: string;
+  /** Reads that file into the terminal while the command runs. */
+  output?: BackgroundOutputTail;
+}
+
+/** A tool call whose task runs on in the background (see `Session.backgroundToolCalls`). */
+export interface BackgroundToolCall {
+  toolCallId: string;
+  /** The tool use of the call, which Claude Code no longer caches after its result. */
+  toolUse: { name: string; input: unknown };
+  /** The subagent tool call that made the call, if any. */
+  parentToolUseId?: string;
+  paused?: boolean;
+}
+
+/** How a background task ended, as Claude Code reports it. Undefined when it did not say. */
+export type BackgroundTaskEnd = "completed" | "failed" | "stopped" | undefined;
+
+/** The live background task set of `background_tasks_changed`, by task id. */
+export type BackgroundLevel = Map<
+  string,
+  { ambient: boolean; taskType: string; description: string; parentTaskId?: string }
+>;
+
+/** The work state of a session, as its `state_update` names it. */
+export type WorkStateName = "idle" | "running" | "requires_action" | "unknown";
+
+/** A new list of the session `sessionId`, with what its repeated state needs. */
+export interface BackgroundReport {
+  sessionId: string;
+  items: BackgroundItem[];
+  /** The session's work state now, or undefined when it has none yet. */
+  state: WorkStateName | undefined;
+  /** The parent of a subagent session, which mirrors the child's state. */
+  parentSessionId?: string;
+}
+
+/** Where the agent reports the lists (see the agent's `background` option). */
+export interface BackgroundSink {
+  /** The list of a session changed, or is reported for the first time. */
+  changed(report: BackgroundReport): void;
+  /** The session ended: its list is no longer reported. */
+  forget(sessionId: string): void;
+}
+
+/**
+ * The state of a session that other modules own, and that the background
+ * work reads: Claude Code's tasks as the consumer tracks them, the subagent
+ * sessions, and the query that stops a task.
+ */
+export interface BackgroundOwner {
+  liveBackgroundTasks: Map<string, { parentToolUseId?: string; isSubagent: boolean }>;
+  nativeSubagentsByTaskId?: Map<string, NativeSubagent>;
+  query: { stopTask(taskId: string): Promise<void> };
+}
+
+/** A task of a `background_tasks_changed` payload. */
+export type LevelTask = {
+  task_id: string;
+  task_type: string;
+  description: string;
+  parent_task_id?: string;
+  ambient?: boolean;
+};
+
+/** The most returned tool calls that {@link SessionBackgroundWork} remembers. */
+const MAX_RETURNED_CALLS = 1024;
+
+/** The tools whose structured result names the task that the call started. */
+const TASK_TOOLS = new Set(["Monitor", "Workflow"]);
+
+/**
+ * The background work of one root session, and of its subagent sessions: the
+ * terminals and tool calls of the tasks that run in the background, and what
+ * the client is told of them.
+ *
+ * Terminals are kept for every client that renders them, as before the
+ * background lists. The rest is kept only when `reported`.
+ */
+export class SessionBackgroundWork {
+  /** Claude Code's live background task set, from its last `background_tasks_changed`. */
+  private level: BackgroundLevel = new Map();
+  /** The terminals of the commands that went to the background, by task id. */
+  private readonly terminals = new Map<string, BackgroundTerminal>();
+  /** The tool calls whose tasks went on in the background, by task id. */
+  private readonly toolCalls = new Map<string, BackgroundToolCall>();
+  /**
+   * The tool calls that returned, oldest first. A task that a call started
+   * is part of that call until it returns, and the foreground work waits on
+   * it. The task's `task_started` can come after the call returned. Bounded
+   * by {@link MAX_RETURNED_CALLS}: a task joins the level around the time its
+   * call returns.
+   */
+  private readonly returned = new Set<string>();
+
+  /**
+   * `reported`: whether the client gets the lists. Only when Claude Code's
+   * interrupt spares background tasks, as `perTaskStopAffordance` makes it.
+   */
+  constructor(
+    private readonly sessionId: string,
+    readonly reported: boolean,
+  ) {}
+
+  /**
+   * Keeps the display terminal of the command `taskId` running after its Bash
+   * result, until its task ends (see `withRunningTerminal`).
+   */
+  terminalStarted(taskId: string, terminal: BackgroundTerminal): void {
+    this.terminals.set(taskId, terminal);
+  }
+
+  /**
+   * Reads what a tool result message tells of the background tasks:
+   *
+   * - The returned calls no longer hold the tasks that they started.
+   * - Each call whose task goes on in the background is registered: a
+   *   `Monitor` or `Workflow` call, whose structured result names its task,
+   *   or a call that a live task names as its tool use, such as a
+   *   backgrounded MCP call. The task must be in the level: one that ended
+   *   already leaves its call as it is. Claude Code marks every live-update
+   *   watcher `ambient`, including the task of a `Monitor` call; a call
+   *   started it, so it is work the client can see and stop, and is
+   *   registered all the same. Ambient tasks without a call of their own,
+   *   such as watchers Claude Code starts by itself, are never registered.
+   *
+   * Returns the ids of the registered calls, whose result then reports
+   * `in_progress` (see `withRunningToolCall`).
+   */
+  toolResults(
+    owner: BackgroundOwner,
+    content: unknown,
+    toolUseResult: unknown,
+    toolUses: Record<string, { name: string; input: unknown }>,
+    parentToolUseId: string | null,
+  ): Set<string> {
+    const registered = new Set<string>();
+    if (!this.reported || !Array.isArray(content)) return registered;
+    const results = content.filter(
+      (block): block is { type: "tool_result"; tool_use_id: string; is_error?: boolean } =>
+        typeof block === "object" &&
+        block !== null &&
+        block.type === "tool_result" &&
+        typeof block.tool_use_id === "string",
+    );
+    for (const { tool_use_id: toolCallId } of results) {
+      this.returned.add(toolCallId);
+      if (this.returned.size > MAX_RETURNED_CALLS) {
+        this.returned.delete(this.returned.values().next().value!);
+      }
+    }
+    const succeeded = results.filter((block) => block.is_error !== true);
+    const structuredTaskId =
+      succeeded.length === 1 &&
+      typeof toolUseResult === "object" &&
+      toolUseResult !== null &&
+      typeof (toolUseResult as { taskId?: unknown }).taskId === "string"
+        ? (toolUseResult as { taskId: string }).taskId
+        : undefined;
+    for (const { tool_use_id: toolCallId } of succeeded) {
+      const toolUse = toolUses[toolCallId];
+      if (!toolUse) continue;
+      const taskId =
+        (TASK_TOOLS.has(toolUse.name) ? structuredTaskId : undefined) ??
+        [...owner.liveBackgroundTasks].find(
+          ([, task]) => task.parentToolUseId === toolCallId && !task.isSubagent,
+        )?.[0];
+      const task = taskId === undefined ? undefined : this.level.get(taskId);
+      if (!task || task.taskType === "local_bash" || task.taskType === "local_agent") {
+        continue;
+      }
+      this.toolCalls.set(taskId!, {
+        toolCallId,
+        toolUse,
+        ...(parentToolUseId ? { parentToolUseId } : {}),
+      });
+      registered.add(toolCallId);
+    }
+    return registered;
+  }
+
+  /**
+   * Starts reading the output of the background command `taskId` into its
+   * terminal, when the client gets the lists and the Bash result named the
+   * command's output file. `send` sends an update of the terminal's tool
+   * call, routed as the call's other updates. Called once the Bash result's
+   * own updates are sent: the first output replaces the placeholder that they
+   * gave the terminal.
+   */
+  followOutput(taskId: string, send: Send): void {
+    const terminal = this.terminals.get(taskId);
+    if (!this.reported || !terminal?.outputFilePath || terminal.output) return;
+    terminal.output = new BackgroundOutputTail(terminal.outputFilePath, (output) =>
+      send(terminalOutputUpdate(this.sessionId, terminal, output)),
+    );
+  }
+
+  /**
+   * The task `taskId` ended. Reads the rest of its command's output, then
+   * exits its terminal, and gives a tool call whose task it was its final
+   * status: `cancelled` for a task that Claude Code stopped, and `completed`
+   * for one that ended without saying how, such as one that the level
+   * dropped: it no longer runs, and reported no failure. Claude Code reports
+   * no exit code for a command, and `completed` does not mean 0: Claude Code
+   * accepts some non-zero codes as a success, such as grep's 1.
+   */
+  async taskEnded(taskId: string, end: BackgroundTaskEnd, send: Send): Promise<void> {
+    const terminal = this.terminals.get(taskId);
+    if (terminal) {
+      await terminal.output?.finish();
+      this.terminals.delete(taskId);
+      await send(terminalExit(this.sessionId, terminal));
+    }
+    const toolCall = this.toolCalls.get(taskId);
+    if (toolCall) {
+      this.toolCalls.delete(taskId);
+      await send(
+        toolCallStatusUpdate(
+          this.sessionId,
+          toolCall,
+          end === "stopped" ? V2_CANCELLED : end === "failed" ? "failed" : "completed",
+        ),
+      );
+    }
+  }
+
+  /**
+   * The update that reports the background tool call of the task `taskId` as
+   * `paused`, or as `in_progress` again, when `paused` changes it. Claude Code
+   * pauses a workflow this way.
+   */
+  taskPaused(taskId: string, paused: boolean): AcpSessionNotification | undefined {
+    const toolCall = this.toolCalls.get(taskId);
+    if (!toolCall || (toolCall.paused ?? false) === paused) return undefined;
+    toolCall.paused = paused;
+    return toolCallStatusUpdate(this.sessionId, toolCall, paused ? V2_PAUSED : "in_progress");
+  }
+
+  /**
+   * Takes Claude Code's new live background task set. The terminals and tool
+   * calls whose tasks it no longer holds end first, before a list drops them,
+   * as v2 requires. A terminal or tool call is registered at its tool result,
+   * after its task joined the level, so a later level without the task means
+   * that it ended. Claude Code usually sends a task's end before that level,
+   * which ends them first, but the SDK does not promise that order.
+   */
+  async levelChanged(tasks: LevelTask[], send: Send): Promise<void> {
+    if (!this.reported) return;
+    const level: BackgroundLevel = new Map(
+      tasks.map((task) => [
+        task.task_id,
+        {
+          ambient: task.ambient === true,
+          taskType: task.task_type,
+          description: task.description,
+          ...(task.parent_task_id !== undefined ? { parentTaskId: task.parent_task_id } : {}),
+        },
+      ]),
+    );
+    for (const taskId of [...this.terminals.keys(), ...this.toolCalls.keys()]) {
+      if (!level.has(taskId)) await this.taskEnded(taskId, undefined, send);
+    }
+    this.level = level;
+  }
+
+  /**
+   * The query closed: Claude Code's background tasks end with its process.
+   * Stops reading output, and returns the updates that exit the root
+   * session's terminals and cancel its tool calls. The level empties, so the
+   * next lists are empty. A subagent's command or tool call is left as it
+   * was: it is on the child's stream, which the closed query's routing owned.
+   */
+  queryClosed(): AcpSessionNotification[] {
+    for (const terminal of this.terminals.values()) terminal.output?.stop();
+    if (!this.reported) return [];
+    const updates: AcpSessionNotification[] = [];
+    for (const [taskId, terminal] of this.terminals) {
+      if (terminal.parentToolUseId) continue;
+      this.terminals.delete(taskId);
+      updates.push(terminalExit(this.sessionId, terminal));
+    }
+    for (const [taskId, toolCall] of this.toolCalls) {
+      if (toolCall.parentToolUseId) continue;
+      this.toolCalls.delete(taskId);
+      updates.push(toolCallStatusUpdate(this.sessionId, toolCall, V2_CANCELLED));
+    }
+    this.level = new Map();
+    this.returned.clear();
+    return updates;
+  }
+
+  /**
+   * The `background` list of the root session and of each of its announced
+   * subagent sessions, with what their repeated states need, deeper sessions
+   * first and the root last: a child's own list goes out before its parent's
+   * list drops it. Each list is empty while the level has not been reported:
+   * Claude Code sends none before the first background task starts.
+   */
+  reports(owner: BackgroundOwner, rootState: WorkStateName): BackgroundReport[] {
+    const children = [...(owner.nativeSubagentsByTaskId ?? [])].filter(
+      ([, child]) => child.announced,
+    );
+    const childByTask = new Map(children);
+    const childByToolUse = new Map(
+      children.flatMap(([, child]) =>
+        child.parentToolUseId ? [[child.parentToolUseId, child] as const] : [],
+      ),
+    );
+    const lists = new Map<string, BackgroundItem[]>([
+      [this.sessionId, []],
+      ...children.map(([, child]): [string, BackgroundItem[]] => [child.sessionId, []]),
+    ]);
+    // A subagent's command or tool call runs on the child's stream.
+    const ownerOf = (parentToolUseId: string | undefined) =>
+      parentToolUseId ? childByToolUse.get(parentToolUseId)?.sessionId : this.sessionId;
+    for (const [taskId, task] of this.level) {
+      // A registered call's task is listed even when ambient, as a `Monitor`
+      // call's is (see `toolResults`).
+      const toolCall = this.toolCalls.get(taskId);
+      if (toolCall) {
+        const session = ownerOf(toolCall.parentToolUseId);
+        if (session)
+          lists.get(session)!.push({ type: "tool_call", toolCallId: toolCall.toolCallId });
+        continue;
+      }
+      if (task.ambient) continue;
+      const terminal = this.terminals.get(taskId);
+      if (terminal) {
+        const session = ownerOf(terminal.parentToolUseId);
+        if (session)
+          lists.get(session)!.push({ type: "terminal", terminalId: terminal.toolCallId });
+        continue;
+      }
+      // A command without a terminal yet is one that foreground work waits on.
+      // A subagent is listed below, as its session.
+      if (task.taskType === "local_bash" || task.taskType === "local_agent") continue;
+      // A task joins the level before its `task_started`, and before the tool
+      // call that starts it returns. Until both, the task is unknown or part
+      // of that tool call.
+      const live = owner.liveBackgroundTasks.get(taskId);
+      if (!live || (live.parentToolUseId && !this.returned.has(live.parentToolUseId))) continue;
+      const parent = task.parentTaskId ? childByTask.get(task.parentTaskId) : undefined;
+      lists
+        .get(parent?.sessionId ?? this.sessionId)!
+        .push({ type: "_claude/task", taskId, description: task.description });
+    }
+    // A child is listed in its parent's list while it works in the background,
+    // and while it is idle with background work of its own. Deeper children
+    // first, so a child's list is whole before its parent's reads it.
+    const sessions = new Map(children.map(([, child]) => [child.sessionId, child]));
+    const depth = (child: NativeSubagent): number => {
+      const parent = sessions.get(child.parentSessionId);
+      return parent ? depth(parent) + 1 : 0;
+    };
+    const ordered = children.sort(([, a], [, b]) => depth(b) - depth(a));
+    for (const [taskId, child] of ordered) {
+      const task = this.level.get(taskId);
+      const working =
+        child.workState !== undefined &&
+        child.workState !== "idle" &&
+        task !== undefined &&
+        !task.ambient;
+      if (working || lists.get(child.sessionId)!.length > 0) {
+        lists.get(child.parentSessionId)?.push({ type: "subagent", sessionId: child.sessionId });
+      }
+    }
+    return [
+      ...ordered.map(([, child]) => ({
+        sessionId: child.sessionId,
+        items: lists.get(child.sessionId)!,
+        state: workStateName(child.workState),
+        parentSessionId: child.parentSessionId,
+      })),
+      { sessionId: this.sessionId, items: lists.get(this.sessionId)!, state: rootState },
+    ];
+  }
+
+  /**
+   * The current state of each background tool call in `toolCallIds`: the
+   * call as `renderer` shows its tool use, with its status now (see
+   * `ClaudeAcpAgent.publishBackgroundToolCalls`).
+   */
+  toolCallStates(
+    toolCallIds: string[],
+    renderer: AcpToolCallRenderer,
+    cwd: string,
+  ): AcpSessionNotification[] {
+    return [...this.toolCalls.values()]
+      .filter((toolCall) => toolCallIds.includes(toolCall.toolCallId))
+      .map((toolCall) => {
+        const update = renderer.toolCall({ id: toolCall.toolCallId, ...toolCall.toolUse }, { cwd });
+        const status = toolCall.paused ? V2_PAUSED : "in_progress";
+        return {
+          sessionId: this.sessionId,
+          update: { ...update, status } as AcpSessionNotification["update"],
+        };
+      });
+  }
+
+  /**
+   * The task of the terminal or tool call `target` that the session
+   * `sessionId` lists, or undefined when it lists no such item.
+   */
+  listedTask(
+    owner: BackgroundOwner,
+    sessionId: string,
+    target: BackgroundTarget,
+  ): string | undefined {
+    if (!this.reported) return undefined;
+    const listed = this.reports(owner, "idle")
+      .find((report) => report.sessionId === sessionId)
+      ?.items.some((item) =>
+        "terminalId" in target
+          ? item.type === "terminal" && item.terminalId === target.terminalId
+          : item.type === "tool_call" && item.toolCallId === target.toolCallId,
+      );
+    if (!listed) return undefined;
+    const id = "terminalId" in target ? target.terminalId : target.toolCallId;
+    const entries = "terminalId" in target ? this.terminals : this.toolCalls;
+    return [...entries].find(([, entry]) => entry.toolCallId === id)?.[0];
+  }
+}
+
+type Send = (notification: AcpSessionNotification) => Promise<void>;
+
+/** A terminal or tool call that `terminal/cancel` or `tool_call/cancel` names. */
+export type BackgroundTarget = { terminalId: string } | { toolCallId: string };
+
+/**
+ * Stops the task of a terminal or tool call that the session `sessionId`
+ * lists (v2 `terminal/cancel` and `tool_call/cancel`). `sessions` are the
+ * root sessions: a subagent session's list is built with its root's. The
+ * terminal exits, or the tool call gets its final status, when Claude Code
+ * reports the task stopped.
+ */
+export async function cancelBackgroundWork(
+  sessions: Array<BackgroundOwner & { background?: SessionBackgroundWork }>,
+  sessionId: string,
+  target: BackgroundTarget,
+): Promise<void> {
+  const notCancellable = () =>
+    "terminalId" in target
+      ? RequestError.invalidParams(
+          { sessionId, terminalId: target.terminalId },
+          `Terminal ${target.terminalId} is not a command running in the background, so it cannot be cancelled.`,
+        )
+      : RequestError.invalidParams(
+          { sessionId, toolCallId: target.toolCallId },
+          `Tool call ${target.toolCallId} is not running in the background, so it cannot be cancelled.`,
+        );
+  for (const session of sessions) {
+    const taskId = session.background?.listedTask(session, sessionId, target);
+    if (taskId === undefined) continue;
+    try {
+      await session.query.stopTask(taskId);
+    } catch (error) {
+      // The task ended meanwhile: it has ended on the client too, or is about to.
+      if (session.background?.listedTask(session, sessionId, target) === undefined) {
+        throw notCancellable();
+      }
+      throw error;
+    }
+    return;
+  }
+  throw notCancellable();
+}
+
+/** The update that gives the terminal of `terminal` the text `output`. */
+function terminalOutputUpdate(
+  sessionId: string,
+  terminal: BackgroundTerminal,
+  output: BackgroundOutput,
+): AcpSessionNotification {
+  const data = { terminal_id: terminal.toolCallId, data: output.text };
+  return {
+    sessionId,
+    update: {
+      sessionUpdate: "tool_call_update",
+      toolCallId: terminal.toolCallId,
+      _meta: {
+        ...(terminal.parentToolUseId
+          ? { claudeCode: { parentToolUseId: terminal.parentToolUseId } }
+          : {}),
+        ...(output.replaces ? { terminal_output: data } : { terminal_output_delta: data }),
+      },
+    },
+  };
+}
+
+/** The update that exits the terminal of `terminal`, with no exit code. */
+function terminalExit(sessionId: string, terminal: BackgroundTerminal): AcpSessionNotification {
+  return {
+    sessionId,
+    update: {
+      sessionUpdate: "tool_call_update",
+      toolCallId: terminal.toolCallId,
+      _meta: {
+        ...(terminal.parentToolUseId
+          ? { claudeCode: { parentToolUseId: terminal.parentToolUseId } }
+          : {}),
+        terminal_exit: { terminal_id: terminal.toolCallId, exit_code: null, signal: null },
+      },
+    },
+  };
+}
+
+function toolCallStatusUpdate(
+  sessionId: string,
+  toolCall: BackgroundToolCall,
+  status: NonNullable<
+    Extract<AcpSessionNotification["update"], { sessionUpdate: "tool_call_update" }>["status"]
+  >,
+): AcpSessionNotification {
+  return {
+    sessionId,
+    update: {
+      sessionUpdate: "tool_call_update",
+      toolCallId: toolCall.toolCallId,
+      status,
+      ...(toolCall.parentToolUseId
+        ? { _meta: { claudeCode: { parentToolUseId: toolCall.parentToolUseId } } }
+        : {}),
+    },
+  };
+}
+
+/**
+ * Publishes the lists of each session that reports them, each time one
+ * changes. The sink sends them to the client synchronously, so a list follows
+ * the updates sent before it.
+ */
+export class BackgroundWorkReporter {
+  /** The list last published for each session, as JSON, and the root session it is built with. */
+  private readonly published = new Map<string, { json: string; root: string }>();
+
+  constructor(private readonly sink?: BackgroundSink) {}
+
+  /** Whether the lists are reported at all. */
+  get enabled(): boolean {
+    return this.sink !== undefined;
+  }
+
+  /**
+   * Publishes each list of the root session `rootSessionId` that changed. The
+   * first call for a session publishes its list, also when it is empty.
+   * `rootState` is the root session's state now.
+   */
+  sync(
+    rootSessionId: string,
+    session: BackgroundOwner & { background?: SessionBackgroundWork },
+    rootState: WorkStateName,
+  ): void {
+    if (!this.sink || !session.background?.reported) return;
+    for (const report of session.background.reports(session, rootState)) {
+      const json = JSON.stringify(report.items);
+      if (this.published.get(report.sessionId)?.json === json) continue;
+      this.published.set(report.sessionId, { json, root: rootSessionId });
+      this.sink.changed(report);
+    }
+  }
+
+  /** The root session `rootSessionId` ended, and its subagent sessions with it. */
+  forget(rootSessionId: string): void {
+    for (const [sessionId, { root }] of this.published) {
+      if (root !== rootSessionId) continue;
+      this.published.delete(sessionId);
+      this.sink?.forget(sessionId);
+    }
+  }
+}
+
+/** A child's work state, when it is one that v2 names. */
+function workStateName(state: string | undefined): WorkStateName | undefined {
+  return state === "idle" ||
+    state === "running" ||
+    state === "requires_action" ||
+    state === "unknown"
+    ? state
+    : undefined;
+}
--- a/src/binary-entry.ts
+++ b/src/binary-entry.ts
@@ -0,0 +1,12 @@
+// Entry of the release executable (`scripts/build-binary.mjs`). It registers the
+// Claude CLI shipped next to the executable before importing the agent:
+// index.ts starts serving (or, with --cli, spawns the CLI) while it evaluates,
+// and a static import would evaluate it before this module's body runs.
+import { realpathSync } from "node:fs";
+import { dirname } from "node:path";
+import { useBundledClaudeCli } from "./claude-cli.js";
+
+// realpath, so a symlink to the executable (e.g. in /usr/local/bin) still finds
+// the CLI next to the real file.
+useBundledClaudeCli(dirname(realpathSync(process.execPath)));
+await import("./index.js");
--- a/src/claude-cli.ts
+++ b/src/claude-cli.ts
@@ -0,0 +1,88 @@
+import { existsSync } from "node:fs";
+import { join } from "node:path";
+
+const CLI_FILE_NAME = process.platform === "win32" ? "claude.exe" : "claude";
+
+let bundledCliDirectory: string | undefined;
+
+/**
+ * Called by the executable's entry (`src/binary-entry.ts`) before the agent
+ * starts. A `bun build --compile` executable has no `node_modules` to resolve
+ * the SDK's platform package from, so the release archive ships the Claude CLI
+ * next to it. The CLI isn't embedded: a child process can't run a file inside
+ * Bun's `$bunfs`, so an embedded copy would have to be extracted to disk first.
+ */
+export function useBundledClaudeCli(directory: string): void {
+  bundledCliDirectory = directory;
+}
+
+/**
+ * The Claude CLI binary to spawn: `CLAUDE_CODE_EXECUTABLE` if set, then the CLI
+ * shipped next to the executable, then the SDK's platform-specific package.
+ */
+export async function claudeCliPath(): Promise<string> {
+  if (process.env.CLAUDE_CODE_EXECUTABLE) {
+    return process.env.CLAUDE_CODE_EXECUTABLE;
+  }
+  if (bundledCliDirectory !== undefined) {
+    return bundledClaudeCliPath(bundledCliDirectory);
+  }
+  return installedClaudeCliPath();
+}
+
+function bundledClaudeCliPath(directory: string): string {
+  const path = join(directory, CLI_FILE_NAME);
+  // Without this check, spawning a missing CLI fails with a bare ENOENT.
+  if (!existsSync(path)) {
+    throw new Error(
+      `The Claude CLI is missing: expected ${path}. Keep ${CLI_FILE_NAME} from the release archive ` +
+        "in the same directory as claude-agent-acp, or set CLAUDE_CODE_EXECUTABLE to a Claude CLI binary.",
+    );
+  }
+  return path;
+}
+
+async function installedClaudeCliPath(): Promise<string> {
+  // The SDK's CLI is a native binary shipped as a platform-specific optional
+  // dependency of @anthropic-ai/claude-agent-sdk. Resolve via a require bound
+  // to the SDK so nested installs are found even when npm doesn't hoist.
+  const { createRequire } = await import("node:module");
+  const req = createRequire(import.meta.resolve("@anthropic-ai/claude-agent-sdk"));
+  const ext = process.platform === "win32" ? ".exe" : "";
+  // On linux, both glibc and musl variants may be installed side-by-side
+  // (e.g. bunx hydrates every optional dep), so picking one by trial is
+  // unreliable: the wrong binary segfaults at runtime instead of failing to
+  // spawn. Detect the runtime libc and prefer the matching variant, falling
+  // back to the other only if the preferred one isn't installed.
+  const candidates =
+    process.platform === "linux"
+      ? isMuslLibc()
+        ? [
+            `@anthropic-ai/claude-agent-sdk-linux-${process.arch}-musl/claude${ext}`,
+            `@anthropic-ai/claude-agent-sdk-linux-${process.arch}/claude${ext}`,
+          ]
+        : [
+            `@anthropic-ai/claude-agent-sdk-linux-${process.arch}/claude${ext}`,
+            `@anthropic-ai/claude-agent-sdk-linux-${process.arch}-musl/claude${ext}`,
+          ]
+      : [`@anthropic-ai/claude-agent-sdk-${process.platform}-${process.arch}/claude${ext}`];
+  for (const candidate of candidates) {
+    try {
+      return req.resolve(candidate);
+    } catch {
+      // try next candidate
+    }
+  }
+  throw new Error(
+    `Claude native binary not found for ${process.platform}-${process.arch}. ` +
+      `Reinstall @anthropic-ai/claude-agent-sdk without --omit=optional, or set CLAUDE_CODE_EXECUTABLE.`,
+  );
+}
+
+function isMuslLibc(): boolean {
+  // process.report.getReport().header.glibcVersionRuntime is populated when
+  // Node is dynamically linked against glibc, and absent on musl.
+  const report = process.report?.getReport() as
+    { header?: { glibcVersionRuntime?: string } } | undefined;
+  return !report?.header?.glibcVersionRuntime;
+}
--- a/src/clear-context-coordinator.ts
+++ b/src/clear-context-coordinator.ts
@@ -45,6 +45,7 @@ export type ClearContextSession<Turn extends ClearContextTurn = ClearContextTurn
  turnQueue?: Turn[];
  pendingExitPlanContextReset?: ClearContextReset;
  contextUsedTokens?: number;
+  contextWindowSize: number;
  sentUserUuids?: Set<string>;
  input: { push(message: SDKUserMessage): unknown };
 };
@@ -61,10 +62,13 @@ export type ClearContextCoordinatorHost<
  ): Promise<Session>;
  applyFastMode(session: Session, enabled: boolean): Promise<void>;
  applyUltracode(session: Session, enabled: boolean): Promise<void>;
+  /** Publishes the fresh context's mode, config options, and usage: the
+   *  context starts empty in a window of `contextWindowSize` tokens. */
  publishSessionState(
    sessionId: string,
    mode: PermissionMode,
    configOptions: SessionConfigOption[],
+    contextWindowSize: number,
  ): Promise<void>;
  continuationMessage(sessionId: string, plan: string, promptUuid: string): SDKUserMessage;
  ensureConsumer(session: Session, sessionId: string): void;
@@ -165,7 +169,12 @@ export async function continuePlanInFreshContext<
  freshSession.contextUsedTokens = 0;

  try {
-    await host.publishSessionState(sessionId, reset.mode, freshSession.configOptions);
+    await host.publishSessionState(
+      sessionId,
+      reset.mode,
+      freshSession.configOptions,
+      freshSession.contextWindowSize,
+    );
  } catch (error) {
    host.logError("Failed to publish clear-context session state:", error);
  }
--- a/src/context-compaction-meta.ts
+++ b/src/context-compaction-meta.ts
@@ -2,7 +2,7 @@ import { AIR_CONTEXT_COMPACTION_KEY, withAirMeta } from "./air-extension.js";

 export const CONTEXT_COMPACTION_META_VERSION = 1;

-export type ContextCompactionTrigger = "manual" | "automatic";
+export type ContextCompactionTrigger = "manual" | "automatic" | "idle";

 export interface ContextCompactionMetadata {
  version: typeof CONTEXT_COMPACTION_META_VERSION;
--- a/src/context-compaction.ts
+++ b/src/context-compaction.ts
@@ -1,6 +1,7 @@
 import { ClientCapabilities, SessionNotification } from "@agentclientprotocol/sdk/unstable";
 import {
  ContextCompactionMetadata,
+  ContextCompactionTrigger,
  createContextCompactionMeta,
 } from "./context-compaction-meta.js";
 import { compactionToolCall } from "./tool-calls/reporters/compaction.js";
@@ -408,14 +409,29 @@ function withoutError({
  return facts;
 }

-export function contextCompactionMetadataFromBoundary(compactMetadata: {
-  trigger: "manual" | "auto";
-  pre_tokens: number;
-  post_tokens?: number;
-  duration_ms?: number;
-}): Omit<ContextCompactionMetadata, "version"> {
+function compactionTrigger(
+  cliTrigger: "manual" | "auto",
+  sentByAdapter: boolean,
+): ContextCompactionTrigger {
+  // The CLI's own automatic compaction stays automatic, even inside the adapter's /compact turn.
+  if (cliTrigger === "auto") return "automatic";
+  // The CLI reports every /compact as manual; only the adapter knows it sent this one itself.
+  if (sentByAdapter) return "idle";
+  return "manual";
+}
+
+/** `idleCompaction` marks a `/compact` that the adapter sent itself (see `IdleCompaction`). */
+export function contextCompactionMetadataFromBoundary(
+  compactMetadata: {
+    trigger: "manual" | "auto";
+    pre_tokens: number;
+    post_tokens?: number;
+    duration_ms?: number;
+  },
+  { idleCompaction = false }: { idleCompaction?: boolean } = {},
+): Omit<ContextCompactionMetadata, "version"> {
  return {
-    trigger: compactMetadata.trigger === "auto" ? "automatic" : "manual",
+    trigger: compactionTrigger(compactMetadata.trigger, idleCompaction),
    preTokens: compactMetadata.pre_tokens,
    ...(compactMetadata.post_tokens !== undefined
      ? { postTokens: compactMetadata.post_tokens }
--- a/src/diff.ts
+++ b/src/diff.ts
@@ -89,7 +89,7 @@ export type PatchForm = "air" | "v2";
 /**
 * How a git patch names its file. `git` is git's own form: the leading slash
 * dropped and the `a/` and `b/` prefixes added. `absolute` is the form of an
- * ACP v2 `git_patch`, whose paths must be absolute: the path itself.
+ * ACP v2 `git_patch`, whose paths must be absolute: the native path itself.
 */
 type GitPatchPaths = "git" | "absolute";

@@ -438,11 +438,11 @@ export function gitPatchText(
 }

 function gitPatchHeader(filePath: string, change: FileChange, paths: GitPatchPaths): string[] {
-  // A Windows path gets forward slashes so the header names the same file on
-  // every platform.
-  const slashed = filePath.replaceAll("\\", "/");
-  // git drops one leading slash of an absolute path.
-  const name = paths === "git" ? slashed.replace(/^\/+/u, "") : slashed;
+  // git's form uses forward slashes, so the header names the same file on
+  // every platform, and drops one leading slash of an absolute path. An ACP v2
+  // patch keeps the native path so that, once unquoted, it equals the `changes`
+  // entry: `C:\work\App.ts` is written `"C:\\work\\App.ts"`.
+  const name = paths === "git" ? filePath.replaceAll("\\", "/").replace(/^\/+/u, "") : filePath;
  const oldName = quoteGitPath(paths === "git" ? "a/" : "", name);
  const newName = quoteGitPath(paths === "git" ? "b/" : "", name);
  // git ends a ---/+++ name that contains a space with a tab, for GNU patch.
--- a/src/elicitation.ts
+++ b/src/elicitation.ts
@@ -1,8 +1,7 @@
 import { randomUUID } from "node:crypto";
-import { CreateElicitationResponse } from "@agentclientprotocol/sdk/unstable";
 import type {
  CreateElicitationRequest,
-  ElicitationAcceptAction,
+  CreateElicitationResponse,
  ElicitationPropertySchema,
  ElicitationSchema,
  EnumOption,
@@ -75,17 +74,22 @@ export function mcpElicitationToCreateRequest(
 }

 /**
- * Content of an accepted elicitation response.
+ * Content of an accepted elicitation response, or `{}` when the response is
+ * no accept or its `content` is no JSON object.
 *
- * Uses the SDK's validating guard rather than an `action === "accept"` check:
- * the guard both narrows past the union's custom/future variant and validates
- * the payload, so a malformed accept (right tag, ill-typed content) yields
- * empty content — the same classification the SDK's wire validators apply.
+ * The values are not checked. v1 allows a string, number, boolean, or string
+ * array; v2 also allows any other JSON value, such as an object. An MCP
+ * server checks the content against its own `requestedSchema`, so it gets the
+ * content as the client sent it: before, an accept whose content held an
+ * object reached the server as `{ action: "accept", content: {} }`. Callers
+ * that read a field must check its type.
 */
-function acceptedElicitationContent(
-  response: CreateElicitationResponse,
-): NonNullable<ElicitationAcceptAction["content"]> {
-  return CreateElicitationResponse.isAccept(response) ? (response.content ?? {}) : {};
+function acceptedElicitationContent(response: CreateElicitationResponse): Record<string, unknown> {
+  if (response.action !== "accept") return {};
+  const content: unknown = (response as { content?: unknown }).content;
+  return content !== null && typeof content === "object" && !Array.isArray(content)
+    ? (content as Record<string, unknown>)
+    : {};
 }

 /**
@@ -97,7 +101,11 @@ export function createElicitationResponseToElicitResult(
 ): ElicitationResult {
  switch (response.action) {
    case "accept":
-      return { action: "accept", content: acceptedElicitationContent(response) };
+      // `ElicitResult` types the values as v1 does. The MCP server checks them.
+      return {
+        action: "accept",
+        content: acceptedElicitationContent(response) as ElicitationResult["content"],
+      };
    case "decline":
      return { action: "decline" };
    case "cancel":
@@ -295,7 +303,7 @@ export function applyAskElicitationResponse(
  questions: AskUserQuestion[],
  options: { reportUnanswered?: boolean } = {},
 ): AskUserQuestionOutcome {
-  // Typed against the output schema: as of SDK 0.3.312 only it lists
+  // Typed against the output schema: as of SDK 0.3.318 only it lists
  // `unanswered`, though the tool reads the same annotations from its input.
  const annotations: NonNullable<AskUserQuestionOutput["annotations"]> = {};
  const withAnnotations = (answers: AskUserQuestionOutput["answers"]) => ({
@@ -325,13 +333,13 @@ export function applyAskElicitationResponse(
    const custom = content[questionCustomFieldKey(index)];
    const customText = typeof custom === "string" ? custom.trim() : "";

+    // A pick is a string, number, or boolean. Other values, such as an object
+    // that a v2 client may send, are dropped instead of read as "[object Object]".
    const value = content[questionFieldKey(index)];
-    const picks: string[] =
-      value === undefined || value === null
-        ? []
-        : Array.isArray(value)
-          ? value.filter((item) => item !== undefined && item !== null && item !== "").map(String)
-          : [String(value)];
+    const picks: string[] = (Array.isArray(value) ? value : [value])
+      .filter(isElicitationScalar)
+      .map(String)
+      .filter((item) => item !== "");

    // A multi-select is additive, and the form offers the selection and the
    // custom box as independent fields — a user who fills both means both, so
@@ -374,10 +382,16 @@ export function applyAskElicitationResponse(
  return { action: "answered", updatedInput: withAnnotations(answers) };
 }

+function isElicitationScalar(value: unknown): value is string | number | boolean {
+  return typeof value === "string" || typeof value === "number" || typeof value === "boolean";
+}
+
 /**
 * Coerce an arbitrary MCP `requestedSchema` into an ACP `ElicitationSchema`.
 * The two are structurally compatible JSON Schemas; we just guarantee the
- * `type: "object"` discriminator is present.
+ * `type: "object"` discriminator and a `properties` map are present. The v2
+ * schema requires both, so a client on SDK 2.2.0 or later rejects an MCP
+ * schema such as `{ type: "object" }` that has no `properties`.
 */
 function normalizeElicitationSchema(
  schema: Record<string, unknown> | undefined,
@@ -385,7 +399,8 @@ function normalizeElicitationSchema(
  if (!schema || typeof schema !== "object") {
    return { type: "object", properties: {} };
  }
-  return { ...(schema as ElicitationSchema), type: "object" };
+  const { properties } = schema as Partial<ElicitationSchema>;
+  return { ...(schema as ElicitationSchema), type: "object", properties: properties ?? {} };
 }

 /**
--- a/src/exit-plan.ts
+++ b/src/exit-plan.ts
@@ -213,7 +213,7 @@ export class ExitPlanCoordinator<
    try {
      const clearContextHost: ClearContextCoordinatorHost<Session, Turn> = {
        ...this.host,
-        publishSessionState: async (id, mode, configOptions) => {
+        publishSessionState: async (id, mode, configOptions, contextWindowSize) => {
          await this.host.sessionUpdate({
            sessionId: id,
            update: { sessionUpdate: "current_mode_update", currentModeId: mode },
@@ -222,6 +222,12 @@ export class ExitPlanCoordinator<
            sessionId: id,
            update: { sessionUpdate: "config_option_update", configOptions },
          });
+          // Otherwise the client shows the old context's usage until the fresh
+          // context first reports its own.
+          await this.host.sessionUpdate({
+            sessionId: id,
+            update: { sessionUpdate: "usage_update", used: 0, size: contextWindowSize },
+          });
          // The approved plan becomes the session's plan once the fresh
          // context that carries it out exists. Its ExitPlanMode ended with
          // an error result, so toAcpNotifications did not publish it.
--- a/src/fork-session.ts
+++ b/src/fork-session.ts
@@ -176,9 +176,37 @@ function resolveFromFullHistory(
  return occurrenceMatches.length === 1 ? occurrenceMatches[0]?.uuid : undefined;
 }

+/**
+ * Whether `error` is the Claude SDK's report that `sessionId` has no
+ * transcript: `forkSession` and `importSessionToStore` throw
+ * `Error("Session <id> not found")`, and both throw
+ * `"Invalid sessionId: <id>"` for an id that is not a UUID.
+ */
+function isUnknownSessionError(error: unknown, sessionId: string): boolean {
+  if (!(error instanceof Error)) return false;
+  return (
+    error.message === `Session ${sessionId} not found` ||
+    error.message === `Invalid sessionId: ${sessionId}`
+  );
+}
+
 export async function forkSession(
  params: ForkSessionRequest,
  dependencies: ForkSessionDependencies,
+): Promise<ForkSessionResponse> {
+  try {
+    return await forkTranscript(params, dependencies);
+  } catch (error) {
+    if (isUnknownSessionError(error, params.sessionId)) {
+      throw RequestError.sessionNotFound(params.sessionId);
+    }
+    throw error;
+  }
+}
+
+async function forkTranscript(
+  params: ForkSessionRequest,
+  dependencies: ForkSessionDependencies,
 ): Promise<ForkSessionResponse> {
  const timing = new SessionTiming(dependencies.logger, "fork", params.sessionId);
  const point = forkPoint(params._meta);
--- a/src/idle-compaction.ts
+++ b/src/idle-compaction.ts
@@ -0,0 +1,240 @@
+export type PromptCacheTtl = "5m" | "1h";
+
+export type IdleCompactionHost = {
+  /** Claude is working (`startTurn`'s check) or a permission request / user input is pending. */
+  isBusy(): boolean;
+  /** Context size after the last main-thread request, or undefined if unknown. */
+  contextTokens(): number | undefined;
+  /** Current merged Claude Code settings. */
+  settings(): {
+    idleCompaction?: boolean;
+    autoCompactEnabled?: boolean;
+    env?: Record<string, string | undefined>;
+  };
+  /** Runs `/compact` as an adapter-originated turn; settles with that turn. */
+  compact(): Promise<unknown>;
+  /** Debug-level log. */
+  log(message: string): void;
+};
+
+export type IdleCompactionOptions = {
+  env?: Record<string, string | undefined>;
+  setTimeout?: (callback: () => void, ms: number) => unknown;
+};
+
+/** The longest delay `setTimeout` takes; a longer one fires at once. */
+const MAX_TIMER_MS = 2_147_483_647;
+const HOUR_MS = 3_600_000;
+const DEFAULT_MIN_TOKENS = 200_000;
+const MIN_TOKENS_FLOOR = 100_000;
+// 54 min for a 1h cache: leaves a margin for the gap between the provider
+// writing the cache and the adapter receiving the response.
+const DEFAULT_DELAY_MS = 0.9 * HOUR_MS;
+// Node timers do not run while the machine sleeps, so one can fire hours after
+// its deadline, on a cache that expired meanwhile. Same threshold as Claude Code.
+const LAPSED_AFTER_MS = 60_000;
+// The values Claude Code reads as "on" for env flags such as DISABLE_COMPACT
+// (case-insensitive, trimmed).
+const TRUTHY_ENV = new Set(["1", "true", "yes", "on"]);
+
+function isTruthyEnv(value: string | undefined): boolean {
+  return value !== undefined && TRUTHY_ENV.has(value.trim().toLowerCase());
+}
+
+function parseCacheTtl(usage: unknown): PromptCacheTtl | undefined {
+  const creation = (usage as { cache_creation?: unknown } | null | undefined)?.cache_creation;
+  if (typeof creation !== "object" || creation === null) return undefined;
+  const { ephemeral_1h_input_tokens: hour, ephemeral_5m_input_tokens: fiveMin } = creation as {
+    ephemeral_1h_input_tokens?: unknown;
+    ephemeral_5m_input_tokens?: unknown;
+  };
+  if (typeof hour === "number" && hour > 0) return "1h";
+  if (typeof fiveMin === "number" && fiveMin > 0) return "5m";
+  return undefined;
+}
+
+/**
+ * Compacts a session shortly before its one-hour prompt cache expires, so the
+ * next prompt writes a short summary instead of the whole context. Claude Code
+ * has this feature but arms it only for "attended" sessions, which SDK sessions
+ * are not. One instance per session.
+ */
+export class IdleCompaction {
+  private readonly env: Record<string, string | undefined>;
+  private readonly setTimer: (callback: () => void, ms: number) => unknown;
+  private ttl: PromptCacheTtl | undefined;
+  private lastRequestAt: number | undefined;
+  private lastMessageId: string | undefined;
+  /** Set when `/compact` was sent, cleared by the next request: a compaction that failed,
+   *  or left the context large, would otherwise re-arm at once and loop until the user prompts. */
+  private compactedSinceLastRequest = false;
+  private timer: unknown;
+  private compacting = false;
+  private disposed = false;
+  private warnedInvalidDelay = false;
+  /** `status` of the last `rate_limit_event`; unknown until one arrives. */
+  private rateLimitStatus: string | undefined;
+
+  constructor(
+    private readonly host: IdleCompactionHost,
+    options: IdleCompactionOptions = {},
+  ) {
+    this.env = options.env ?? process.env;
+    this.setTimer = options.setTimeout ?? ((cb, ms) => setTimeout(cb, ms));
+  }
+
+  /** Whether an idle compaction it started is still running. `acp-agent.ts` reports
+   *  `trigger: "idle"` while it is true. A client's `/compact` queued behind is read
+   *  only after the adapter's turn's `result`, which clears `compacting`; this relies
+   *  on the CLI emitting that compaction's `compact_boundary` after the previous
+   *  result, which nothing here enforces. */
+  get isCompacting(): boolean {
+    return this.compacting;
+  }
+
+  /** A main-thread response arrived. Records its time and cache TTL, and drops any armed timer.
+   *  The provider writes the cache when the request starts, so the deadline is measured from the
+   *  response's first sighting: the `message_start` stream event, or its first `assistant` message
+   *  when it was not streamed. The CLI sends one `assistant` message per content block, and a
+   *  7-minute response would otherwise put the deadline 7 minutes after the cache was written.
+   *  A later call with the same `messageId` only updates the TTL. */
+  noteRequest(usage: unknown, messageId?: string): void {
+    if (this.disposed) return;
+    this.ttl = parseCacheTtl(usage) ?? this.ttl;
+    if (messageId !== undefined && messageId === this.lastMessageId) return;
+    this.lastMessageId = messageId;
+    this.lastRequestAt = Date.now();
+    this.compactedSinceLastRequest = false;
+    this.disarm("new request");
+  }
+
+  /** The session became idle. Arms the timer if every condition holds, else logs why not. */
+  onIdle(): void {
+    if (this.disposed) return;
+    const skip = this.skipReason();
+    if (skip) {
+      this.host.log(`[idle-compaction] skip: ${skip}`);
+      return;
+    }
+    this.disarm("rearm");
+    const deadline = this.lastRequestAt! + this.delayMs();
+    this.timer = this.setTimer(() => void this.fire(), Math.max(0, deadline - Date.now()));
+    (this.timer as { unref?: () => void } | undefined)?.unref?.();
+    this.host.log(`[idle-compaction] armed deadline=${new Date(deadline).toISOString()}`);
+  }
+
+  /** A `rate_limit_event` arrived (`SDKRateLimitInfo`). Anything but `allowed` skips compaction,
+   *  as in Claude Code. This is account state, so `reset()` keeps it. */
+  noteRateLimit(info: unknown): void {
+    const status = (info as { status?: unknown } | null | undefined)?.status;
+    if (typeof status === "string") this.rateLimitStatus = status;
+  }
+
+  /** Claude Code reported its compaction as failed. Its turn still ends normally, so `compact()` does not reject. */
+  noteCompactionFailed(error: string | undefined): void {
+    if (!this.compacting) return;
+    this.host.log(`[idle-compaction] compaction failed: ${error ?? "no reason given"}`);
+  }
+
+  /** The conversation was replaced (`/clear`): forgets the recorded request and TTL, and drops any armed timer. */
+  reset(): void {
+    this.ttl = undefined;
+    this.lastRequestAt = undefined;
+    this.lastMessageId = undefined;
+    this.compactedSinceLastRequest = false;
+    this.disarm("conversation reset");
+  }
+
+  /** Drops the armed timer, if any. `reason` is only logged. */
+  disarm(reason: string): void {
+    if (this.timer === undefined) return;
+    clearTimeout(this.timer as ReturnType<typeof setTimeout>);
+    this.timer = undefined;
+    this.host.log(`[idle-compaction] disarmed: ${reason}`);
+  }
+
+  /** Disarms and ignores every later call. */
+  dispose(): void {
+    this.disarm("disposed");
+    this.disposed = true;
+  }
+
+  private async fire(): Promise<void> {
+    this.timer = undefined;
+    if (this.disposed) return;
+    const skip = this.skipReason();
+    if (skip) {
+      this.host.log(`[idle-compaction] skip at fire: ${skip}`);
+      return;
+    }
+    this.host.log("[idle-compaction] firing /compact");
+    this.compacting = true;
+    this.compactedSinceLastRequest = true;
+    try {
+      await this.host.compact();
+    } catch (error) {
+      this.host.log(`[idle-compaction] compaction failed: ${error}`);
+    } finally {
+      this.compacting = false;
+    }
+  }
+
+  /** Why no compaction should be scheduled right now, or undefined if all conditions hold. */
+  private skipReason(): string | undefined {
+    if (this.compacting) return "compaction already running";
+    const disabled = this.disabledBy();
+    if (disabled) return `disabled by ${disabled}`;
+    if (this.lastRequestAt === undefined) return "no request recorded in this process";
+    if (Date.now() > this.lastRequestAt + this.delayMs() + LAPSED_AFTER_MS) {
+      return "cache lapsed: more than 60 s past the deadline";
+    }
+    if (this.rateLimitStatus !== undefined && this.rateLimitStatus !== "allowed") {
+      return `rate limit status is ${this.rateLimitStatus}`;
+    }
+    if (this.compactedSinceLastRequest) return "already compacted for this request";
+    if (this.ttl !== "1h") return `cache TTL is ${this.ttl ?? "unknown"}, not 1h`;
+    const tokens = this.host.contextTokens();
+    const min = this.minTokens();
+    if (tokens === undefined || tokens < min) {
+      return `context ${tokens ?? "unknown"} tokens is below the ${min} minimum`;
+    }
+    if (this.host.isBusy()) return "session is busy";
+    return undefined;
+  }
+
+  private disabledBy(): string | undefined {
+    const settings = this.host.settings();
+    if (settings.idleCompaction === false) return "idleCompaction setting";
+    if (settings.autoCompactEnabled === false) return "autoCompactEnabled setting";
+    for (const name of ["DISABLE_COMPACT", "DISABLE_AUTO_COMPACT"]) {
+      if (isTruthyEnv(this.claudeCodeEnv(name))) return name;
+    }
+    return undefined;
+  }
+
+  /** The CLI applies the settings `env` block after the launch env, so it wins. */
+  private claudeCodeEnv(name: string): string | undefined {
+    return this.host.settings().env?.[name] ?? this.env[name];
+  }
+
+  /** `0` and invalid values fall back to 200,000, as in the CLI, which declares the variable
+   *  with `min: 1` and computes `Math.max(100000, env ?? 200000)`. */
+  private minTokens(): number {
+    const raw = this.claudeCodeEnv("CLAUDE_CODE_IDLE_COMPACT_MIN_TOKENS");
+    const parsed = raw !== undefined && /^\d+$/.test(raw.trim()) ? Number(raw.trim()) : 0;
+    return Math.max(MIN_TOKENS_FLOOR, parsed > 0 ? parsed : DEFAULT_MIN_TOKENS);
+  }
+
+  private delayMs(): number {
+    const raw = this.env.CLAUDE_AGENT_ACP_IDLE_COMPACT_DELAY_MS;
+    if (raw === undefined) return DEFAULT_DELAY_MS;
+    if (/^\d+$/.test(raw.trim()) && Number(raw.trim()) <= MAX_TIMER_MS) return Number(raw.trim());
+    if (!this.warnedInvalidDelay) {
+      this.warnedInvalidDelay = true;
+      this.host.log(
+        `[idle-compaction] ignoring invalid CLAUDE_AGENT_ACP_IDLE_COMPACT_DELAY_MS=${raw}`,
+      );
+    }
+    return DEFAULT_DELAY_MS;
+  }
+}
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,6 @@
 #!/usr/bin/env node

-import { claudeCliPath } from "./acp-agent.js";
+import { claudeCliPath } from "./claude-cli.js";
 import { applyManagedPolicyEnv } from "./managed-policy.js";
 import { acpProtocolsFromEnv, serveAcp } from "./serve.js";
 import packageJson from "../package.json" with { type: "json" };
--- a/src/mcp-command.ts
+++ b/src/mcp-command.ts
@@ -111,8 +111,11 @@ function needsReconnect(status: McpServerStatus): boolean {
 function codeSpan(text: string): string {
  const longestRun = Math.max(0, ...(text.match(/`+/g) ?? []).map((run) => run.length));
  const fence = "`".repeat(longestRun + 1);
-  // CommonMark strips one space from each end of a span, so a pad keeps the text unchanged.
-  const pad = text.startsWith("`") || text.endsWith("`") || /^ .*[^ ].* $/.test(text) ? " " : "";
+  // CommonMark strips one space from each end of a span that is not all spaces
+  // (line endings count as spaces), so a pad keeps the text unchanged. Plain
+  // string checks, not one regex: `^ .*[^ ].* $` backtracks quadratically.
+  const strippedByCommonMark = text.startsWith(" ") && text.endsWith(" ") && /[^ \r\n]/.test(text);
+  const pad = text.startsWith("`") || text.endsWith("`") || strippedByCommonMark ? " " : "";
  return `${fence}${pad}${text}${pad}${fence}`;
 }

--- a/src/native-subagents.ts
+++ b/src/native-subagents.ts
@@ -3,6 +3,8 @@ import {
  type SessionConfigOption,
  type SessionNotification,
 } from "@agentclientprotocol/sdk/unstable";
+import { realpath } from "node:fs/promises";
+import path from "node:path";
 import type { AcpSessionNotification, SubagentForm, SubagentState } from "./acp-subagents.js";
 import { AIR_SUBAGENT_KEY, airExtensionMeta } from "./air-extension.js";
 import { MODEL_CONFIG_ID } from "./session-model.js";
@@ -56,14 +58,23 @@ export type NativeSubagent = {
  /** The RFD form: the calls that delegated to the child, whose runs handed back a report. */
  handedBack?: Set<string>;
  announced?: boolean;
+  /**
+   * The RFD form: the `cwd` that the client holds for the child. Undefined or
+   * null while the child inherits its parent's working directory.
+   */
+  reportedCwd?: string | null;
  terminalState?: SubagentState;
  /** Connection-local single-flight state; never serialized on the wire. */
  announcePromise?: Promise<void>;
+  /** Connection-local: serializes the child's `cwd` reports; never serialized on the wire. */
+  cwdPublishing?: Promise<void>;
  /** Connection-local single-flight state; never serialized on the wire. */
  terminalPromise?: Promise<void>;
 };

 export type NativeSubagentSession = {
+  /** The working directory of the root session, which a child inherits unless it reports its own. */
+  cwd?: string;
  nativeSubagentsByTaskId?: Map<string, NativeSubagent>;
  nativeSubagentTaskIdByToolUseId?: Map<string, string>;
  nativeSubagentParentByToolUseId?: Map<string, string>;
@@ -133,6 +144,8 @@ export type HistoricalSubagent = {
  launchId: string;
  /** The agent that made that call. None means the root session. */
  parentAgentId?: string;
+  /** Its working directory, when Claude Code placed it elsewhere, e.g. in a worktree. */
+  cwd?: string;
  name?: string;
  agentType?: string;
  description?: string;
@@ -172,6 +185,11 @@ export class NativeSubagentRuntime {
  private readonly identityByToolUse = new Map<string, SubagentIdentity>();
  private readonly controlByToolUse = new Map<string, AcpSessionNotification>();
  private readonly configBySession = new Map<string, ChildConfiguration>();
+  /**
+   * The RFD form: the working directory of each child, by session id, as its
+   * hooks last reported it. A hook can come before the child is announced.
+   */
+  private readonly cwdBySession = new Map<string, string>();
  private readonly childByParentToolUse = new Map<string, NativeSubagent>();
  /**
   * The child session of each tool call that went to a child session. A later
@@ -274,6 +292,30 @@ export class NativeSubagentRuntime {
    return child?.announced ? child.workState : undefined;
  }

+  /**
+   * The RFD form: the `subagent_update` that tells a client that holds nothing
+   * of the announced child `sessionId` of this live session what it is now:
+   * its labels, its directory, its `cancel` capability, and its work state.
+   * Undefined when no such child runs here.
+   */
+  currentUpdate(sessionId: string): AcpSessionNotification | undefined {
+    if (this.form !== "rfd") return undefined;
+    const child = this.childOfSession(sessionId);
+    if (!child?.announced || !child.workState) return undefined;
+    return {
+      sessionId: child.parentSessionId,
+      update: {
+        sessionUpdate: "subagent_update",
+        sessionId: child.sessionId,
+        ...(child.title ? { title: child.title } : {}),
+        ...(child.description ? { description: child.description } : {}),
+        ...(child.reportedCwd ? { cwd: child.reportedCwd } : {}),
+        capabilities: { cancel: {} },
+        state: { state: child.workState },
+      },
+    };
+  }
+
  /**
   * Reports the model of a child response, an exact model id, as the entry of
   * the root session's `model` option that matches it, else as the id (see
@@ -400,6 +442,83 @@ export class NativeSubagentRuntime {
    await publishing;
  }

+  /**
+   * The RFD form: takes the working directory of the child `agentId`, the
+   * `cwd` of one of its hooks. A child that Claude Code runs in its own
+   * worktree (Agent `isolation: "worktree"`) reports the worktree. The client
+   * gets the `cwd` only when it differs from the parent's, in the
+   * announcement or in a `subagent_update` right after it. Claude Code runs a
+   * child's SubagentStart hook before its first model request, so the `cwd`
+   * reaches the client before the child's first tool call.
+   */
+  async reportCwd(agentId: string, cwd: string): Promise<void> {
+    if (this.form !== "rfd" || agentId === this.rootSessionId || !path.isAbsolute(cwd)) return;
+    const known = this.children.get(agentId) ?? this.childOfSession(agentId);
+    const sessionId = known?.sessionId ?? agentId;
+    if (!known && !this.cwdBySession.has(sessionId)) {
+      const pending = [...this.cwdBySession.keys()].filter((id) => !this.childOfSession(id)).length;
+      if (pending >= MAX_PENDING_PARENTS) {
+        this.logger.log(
+          `Session ${this.rootSessionId}: dropping cwd for unannounced subagent ${agentId}; pending buffer limit reached`,
+        );
+        return;
+      }
+    }
+    this.cwdBySession.set(sessionId, cwd);
+    if (!known) return;
+    // An announcement in flight may have been built without this `cwd`.
+    if (known.announcePromise) await known.announcePromise.catch(() => {});
+    if (known.announced) await this.publishCwd(known);
+  }
+
+  /**
+   * The `cwd` of `child` that the client does not hold yet: its working
+   * directory when that differs from its parent's, `null` when it is back in
+   * the parent's after it reported another, else undefined.
+   */
+  private async unreportedCwd(child: NativeSubagent): Promise<string | null | undefined> {
+    const cwd = this.cwdBySession.get(child.sessionId);
+    if (cwd === undefined) return undefined;
+    const inherited = this.effectiveCwd(child.parentSessionId);
+    if (inherited !== undefined && (await sameDirectory(cwd, inherited))) {
+      return child.reportedCwd ? null : undefined;
+    }
+    return cwd === child.reportedCwd ? undefined : cwd;
+  }
+
+  /**
+   * The working directory of the session `sessionId` as the client holds it:
+   * the root's from session setup, a child's reported `cwd`, else its
+   * parent's.
+   */
+  private effectiveCwd(sessionId: string): string | undefined {
+    const seen = new Set<string>();
+    let child = this.childOfSession(sessionId);
+    while (child && !seen.has(child.sessionId)) {
+      if (child.reportedCwd) return child.reportedCwd;
+      seen.add(child.sessionId);
+      child = this.childOfSession(child.parentSessionId);
+    }
+    return this.session.cwd;
+  }
+
+  /** The RFD form: sends the `cwd` of the announced `child` that the client does not hold. */
+  private async publishCwd(child: NativeSubagent): Promise<void> {
+    if (this.form !== "rfd") return;
+    // Concurrent hooks of one child report the same `cwd` once.
+    const publishing = (child.cwdPublishing ?? Promise.resolve()).then(async () => {
+      const cwd = await this.unreportedCwd(child);
+      if (cwd === undefined) return;
+      await this.publish({
+        sessionId: child.parentSessionId,
+        update: { sessionUpdate: "subagent_update", sessionId: child.sessionId, cwd },
+      });
+      child.reportedCwd = cwd;
+    });
+    child.cwdPublishing = publishing.catch(() => {});
+    await publishing;
+  }
+
  private async routeUpdate(
    notification: AcpSessionNotification,
    deliver: Publish,
@@ -923,9 +1042,14 @@ export class NativeSubagentRuntime {
        this.childByParentToolUse.set(entry.launchId, child);
      }
      if (child.announced) continue;
+      // A hook of the resumed agent may have reported a newer `cwd`.
+      if (entry.cwd && !this.cwdBySession.has(child.sessionId)) {
+        this.cwdBySession.set(child.sessionId, entry.cwd);
+      }
      if (entry.agentId === agentId) {
        await this.announce(child);
      } else {
+        const cwd = await this.unreportedCwd(child);
        await this.publish({
          sessionId: child.parentSessionId,
          update: {
@@ -933,8 +1057,10 @@ export class NativeSubagentRuntime {
            sessionId: child.sessionId,
            ...(child.title ? { title: child.title } : {}),
            ...(child.description ? { description: child.description } : {}),
+            ...(cwd ? { cwd } : {}),
          },
        });
+        if (cwd) child.reportedCwd = cwd;
        child.announced = true;
      }
      for (const pending of this.takePending(entry.launchId)) await deliver(pending);
@@ -1103,6 +1229,7 @@ export class NativeSubagentRuntime {
  private withdraw(taskId: string, child: NativeSubagent): void {
    this.children.delete(taskId);
    this.configBySession.delete(child.sessionId);
+    this.cwdBySession.delete(child.sessionId);
    if (child.parentToolUseId) {
      this.takePending(child.parentToolUseId);
      this.cleanupControl(child.parentToolUseId);
@@ -1125,12 +1252,16 @@ export class NativeSubagentRuntime {
  }

  /**
-   * Announces `child` in the client's form, then its configuration. A runtime
-   * without a form never does.
+   * Announces `child` in the client's form, with its `cwd` in the RFD form,
+   * then its configuration. A runtime without a form never does.
   */
  private async announce(child: NativeSubagent): Promise<void> {
    if (!this.form) return;
-    await announceNativeSubagent(child, this.publish, this.form);
+    const cwd =
+      this.form === "rfd" && !child.announced ? await this.unreportedCwd(child) : undefined;
+    await announceNativeSubagent(child, this.publish, this.form, cwd ?? undefined);
+    // A hook that reported a `cwd` while the announcement was being built.
+    await this.publishCwd(child);
    await this.publishConfiguration(child);
  }

@@ -1396,6 +1527,7 @@ export class NativeSubagentRuntime {
    this.identityByToolUse.clear();
    this.controlByToolUse.clear();
    this.configBySession.clear();
+    this.cwdBySession.clear();
    this.childByParentToolUse.clear();
    this.taskFinishPromises.clear();
    this.senderByToolUse.clear();
@@ -1601,6 +1733,7 @@ export async function announceNativeSubagent(
  child: NativeSubagent,
  publish: Publish,
  form: SubagentForm,
+  cwd?: string,
 ): Promise<void> {
  if (child.announced) return;
  if (child.announcePromise) return child.announcePromise;
@@ -1614,10 +1747,12 @@ export async function announceNativeSubagent(
          sessionId: child.sessionId,
          ...(child.title ? { title: child.title } : {}),
          ...(child.description ? { description: child.description } : {}),
+          ...(cwd ? { cwd } : {}),
          capabilities: { cancel: {} },
          state: { state: "running" },
        },
      });
+      if (cwd) child.reportedCwd = cwd;
      child.announced = true;
      // The immediate parent made the Agent/Task call that launched the child.
      if (child.prompt) {
@@ -2155,3 +2290,15 @@ function promptField(prompt: string | undefined): { prompt?: string } {
 function nonBlankString(value: unknown): string | undefined {
  return typeof value === "string" && value.trim().length > 0 ? value.trim() : undefined;
 }
+
+/**
+ * Whether `left` and `right` are the same directory, also when one is
+ * spelled through a symlink, e.g. `/tmp/project` and `/private/tmp/project`
+ * on macOS. A path that does not exist is compared as written.
+ */
+export async function sameDirectory(left: string, right: string): Promise<boolean> {
+  if (path.resolve(left) === path.resolve(right)) return true;
+  const real = (dir: string) => realpath(dir).catch(() => path.resolve(dir));
+  const [realLeft, realRight] = await Promise.all([real(left), real(right)]);
+  return realLeft === realRight;
+}
--- a/src/permissions/modes.ts
+++ b/src/permissions/modes.ts
@@ -1,4 +1,4 @@
-import type { PermissionMode } from "@anthropic-ai/claude-agent-sdk";
+import type { PermissionMode, Settings } from "@anthropic-ai/claude-agent-sdk";

 interface PermissionModeLogger {
  error: (...args: unknown[]) => void;
@@ -58,3 +58,10 @@ export function resolvePermissionMode(

  return mapped;
 }
+
+/** Claude Code reads `disableAutoMode` both at the top level and under `permissions`. */
+export function autoModeDisabled(settings: Settings): boolean {
+  return (
+    settings.disableAutoMode === "disable" || settings.permissions?.disableAutoMode === "disable"
+  );
+}
--- a/src/session-index/service.ts
+++ b/src/session-index/service.ts
@@ -387,16 +387,6 @@ function isSdkNotFound(error: unknown): boolean {
  return error instanceof Error && /^Session \S+ not found in /.test(error.message);
 }

-/** The error the SDK `deleteSession` gives for a session id it rejects or
- *  does not find, which a client without `sessionIndex` got before. */
-function sdkDeleteError(sessionId: string): Error {
-  return new Error(
-    isSessionId(sessionId)
-      ? `Session ${sessionId} not found in any project directory`
-      : `Invalid sessionId: ${sessionId}`,
-  );
-}
-
 /**
 * `session/delete` of a client that is neither AIR nor a `sessionIndex` client:
 * the SDK delete of the session's transcript. A session without one succeeds,
@@ -422,16 +412,18 @@ export async function deleteSessionIfStored(
 /**
 * `session/delete` of an AIR client without `sessionIndex`, which uses delete
 * to mark a session done: archives it instead, so the transcript survives. A
- * session without a transcript fails as the SDK delete did.
+ * session without a transcript has nothing to archive and succeeds, as ACP
+ * asks of a delete of a session that never existed (see
+ * {@link deleteSessionIfStored}).
 */
 export async function archiveInsteadOfDelete(
  sessionId: string,
  service: SessionIndexService,
 ): Promise<void> {
-  if (!isSessionId(sessionId)) throw sdkDeleteError(sessionId);
+  if (!isSessionId(sessionId)) return;
  // The SDK delete skips empty transcripts, so they do not count.
  const found = await service.index.findTranscripts(sessionId);
-  if (found.length === 0) throw sdkDeleteError(sessionId);
+  if (found.length === 0) return;
  await service.retitle(sessionId, archiveTo(true), { sidecar: "existing" });
 }

--- a/src/session-mode.ts
+++ b/src/session-mode.ts
@@ -66,29 +66,50 @@ type ModeConfigSession = SessionMode & {
  configOptions: SessionConfigOption[];
 };

-type InitializeSessionModeParams = {
-  query: Pick<Query, "setPermissionMode">;
-  requestedMode: PermissionMode;
-  currentModelInfo?: ModelInfo;
-  currentModelId: string;
+/** Which optional modes the session's mode catalog offers. */
+export type ModeAvailability = {
  /** When false, bypassPermissions is omitted from the mode catalog. */
  allowBypass: boolean;
+  /** When false (`disableAutoMode: "disable"` in settings), auto is omitted. */
+  allowAuto: boolean;
+};
+
+type InitializeSessionModeParams = ModeAvailability & {
+  query: Pick<Query, "setPermissionMode">;
+  requestedMode: PermissionMode;
+  /** The mode is the built-in default: no request, transcript or setting chose it. */
+  builtInDefault?: boolean;
+  currentModelInfo?: ModelInfo;
+  currentModelId: string;
 };

 /**
 * The permission mode a new Claude query starts in.
 *
 * An explicit mode wins. A resume or a load continues in the mode of the last
- * user record of the transcript. If that mode is unknown or not available now,
- * for example bypass, the session starts in `defaultMode` of the settings.
+ * user record of the transcript. If that mode is unknown or absent from the
+ * session's mode catalog, use an available `defaultMode` from settings, or
+ * `default` when that setting is unavailable too.
+ *
+ * With no `defaultMode` set, the session starts in `auto` when the catalog
+ * offers it and in `default` otherwise (`builtInDefault: true`), like an
+ * interactive Claude Code session. Claude Code also starts organizations with
+ * the HIPAA configuration in `default`; the SDK does not report that
+ * configuration, so those sessions start in `auto` here.
 */
 export function resolveInitialPermissionMode(
  sources: { explicit?: PermissionMode; resumed?: string; defaultMode?: unknown },
  logger: { error: (...args: unknown[]) => void },
-  allowBypass: boolean,
-): PermissionMode {
+  availability: ModeAvailability,
+): { mode: PermissionMode; builtInDefault: boolean } {
+  const { allowBypass } = availability;
+  const available = (mode: PermissionMode) =>
+    buildAvailableModes(availability).some((entry) => entry.id === mode);
  if (sources.explicit !== undefined) {
-    return resolvePermissionMode(sources.explicit, logger, allowBypass);
+    return {
+      mode: resolvePermissionMode(sources.explicit, logger, allowBypass),
+      builtInDefault: false,
+    };
  }
  if (sources.resumed !== undefined) {
    let rejected = false;
@@ -97,13 +118,23 @@ export function resolveInitialPermissionMode(
      { error: () => (rejected = true) },
      allowBypass,
    );
-    if (!rejected) return mode;
+    if (!rejected && available(mode)) {
+      return { mode, builtInDefault: false };
+    }
    logger.error(
      `Ignoring permission mode "${sources.resumed}" of the resumed transcript: ` +
        `not available in this session.`,
    );
  }
-  return resolvePermissionMode(sources.defaultMode, logger, allowBypass);
+  if (sources.defaultMode === undefined) {
+    return { mode: available("auto") ? "auto" : "default", builtInDefault: true };
+  }
+  const configuredMode = resolvePermissionMode(sources.defaultMode, logger, allowBypass);
+  // A rejected transcript mode falls back only to a mode this session can offer.
+  if (sources.resumed !== undefined && !available(configuredMode)) {
+    return { mode: "default", builtInDefault: false };
+  }
+  return { mode: configuredMode, builtInDefault: false };
 }

 /** Owns session-mode policy and the ACP/SDK synchronization it requires. */
@@ -113,22 +144,40 @@ export class SessionModeManager<S extends SessionMode> {
  async initialize({
    query,
    requestedMode,
+    builtInDefault = false,
    currentModelInfo,
    currentModelId,
    allowBypass,
+    allowAuto,
  }: InitializeSessionModeParams): Promise<{
    modes: SessionModeState;
    autoModeFallbackWarningPending: boolean;
  }> {
-    const availableModes = this.buildAvailableModes(allowBypass);
+    const availableModes = buildAvailableModes(
+      { allowBypass, allowAuto },
+      this.options.airClient?.() ?? false,
+    );
    let effectiveMode = requestedMode;
    let autoModeFallbackWarningPending = false;

-    if (
+    const autoUnsupported =
      effectiveMode === "auto" &&
      currentModelInfo !== undefined &&
-      currentModelInfo.supportsAutoMode !== true
-    ) {
+      currentModelInfo.supportsAutoMode !== true;
+    if (!this.isAvailable(availableModes, effectiveMode)) {
+      this.options.logError(
+        `permissions.defaultMode "${effectiveMode}" is not available in ` +
+          `this session; falling back to "default".`,
+      );
+      effectiveMode = "default";
+      await this.trySyncMode(query, effectiveMode, "Failed to sync clamped permissionMode to SDK:");
+    } else if (autoUnsupported && builtInDefault) {
+      // Like Claude Code: a built-in Auto default the model can't serve starts
+      // in Manual, without a warning. Nobody chose Auto, so don't escalate to
+      // acceptEdits.
+      effectiveMode = "default";
+      await this.trySyncMode(query, effectiveMode, "Failed to sync clamped permissionMode to SDK:");
+    } else if (autoUnsupported) {
      this.options.logError(
        `permissions.defaultMode "auto" is not available for model ` +
          `"${currentModelId}"; falling back to "${AUTO_MODE_FALLBACK}".`,
@@ -136,13 +185,6 @@ export class SessionModeManager<S extends SessionMode> {
      effectiveMode = AUTO_MODE_FALLBACK;
      autoModeFallbackWarningPending = true;
      await this.trySyncMode(query, effectiveMode, "Failed to sync clamped permissionMode to SDK:");
-    } else if (!this.isAvailable(availableModes, effectiveMode)) {
-      this.options.logError(
-        `permissions.defaultMode "${effectiveMode}" is not available in ` +
-          `this session; falling back to "default".`,
-      );
-      effectiveMode = "default";
-      await this.trySyncMode(query, effectiveMode, "Failed to sync clamped permissionMode to SDK:");
    }

    return {
@@ -350,50 +392,6 @@ export class SessionModeManager<S extends SessionMode> {
    }
  }

-  private buildAvailableModes(allowBypass: boolean): SessionModeState["availableModes"] {
-    // Only AIR gets the mode kind.
-    const air = this.options.airClient?.() ?? false;
-    const kind = (value: string) => {
-      const meta = airOnlyMeta(air, AIR_KIND_KEY, value);
-      return meta ? { _meta: meta } : {};
-    };
-    const modes: SessionModeState["availableModes"] = [
-      {
-        id: "default",
-        name: "Manual",
-        description: "Always ask before making changes",
-        ...kind("standard"),
-      },
-      {
-        id: "acceptEdits",
-        name: "Accept edits",
-        description: "Automatically accept all file edits",
-        ...kind("standard"),
-      },
-      {
-        id: "plan",
-        name: "Plan",
-        description: "Create a plan before making changes",
-        ...kind("plan"),
-      },
-      {
-        id: "auto",
-        name: "Auto",
-        description: "Claude handles permission decisions",
-        ...kind("auto_review"),
-      },
-    ];
-    if (allowBypass) {
-      modes.push({
-        id: "bypassPermissions",
-        name: "Bypass permissions",
-        description: "Accepts all permissions",
-        ...kind("full_access"),
-      });
-    }
-    return modes;
-  }
-
  private async trySyncMode(
    query: Pick<Query, "setPermissionMode">,
    mode: PermissionMode,
@@ -406,3 +404,51 @@ export class SessionModeManager<S extends SessionMode> {
    }
  }
 }
+
+function buildAvailableModes(
+  { allowBypass, allowAuto }: ModeAvailability,
+  air = false,
+): SessionModeState["availableModes"] {
+  // Only AIR gets the mode kind.
+  const kind = (value: string) => {
+    const meta = airOnlyMeta(air, AIR_KIND_KEY, value);
+    return meta ? { _meta: meta } : {};
+  };
+  const modes: SessionModeState["availableModes"] = [
+    {
+      id: "default",
+      name: "Manual",
+      description: "Always ask before making changes",
+      ...kind("standard"),
+    },
+    {
+      id: "acceptEdits",
+      name: "Accept edits",
+      description: "Automatically accept all file edits",
+      ...kind("standard"),
+    },
+    {
+      id: "plan",
+      name: "Plan",
+      description: "Create a plan before making changes",
+      ...kind("plan"),
+    },
+  ];
+  if (allowAuto) {
+    modes.push({
+      id: "auto",
+      name: "Auto",
+      description: "Claude handles permission decisions",
+      ...kind("auto_review"),
+    });
+  }
+  if (allowBypass) {
+    modes.push({
+      id: "bypassPermissions",
+      name: "Bypass permissions",
+      description: "Accepts all permissions",
+      ...kind("full_access"),
+    });
+  }
+  return modes;
+}
--- a/src/session-ultracode.ts
+++ b/src/session-ultracode.ts
@@ -25,7 +25,7 @@ export type UltracodeSettingsReport = {
 };

 // `Query.getSettings()` exists at runtime (sdk.mjs) but is missing from the
-// SDK's type declarations as of 0.3.312.
+// SDK's type declarations as of 0.3.318.
 type GetSettingsQuery = Query & {
  getSettings?: () => Promise<{
    applied?: { ultracodeAvailable?: unknown; ultracodeRequested?: unknown };
--- a/src/startup-failure.ts
+++ b/src/startup-failure.ts
@@ -0,0 +1,42 @@
+import { RequestError } from "@agentclientprotocol/sdk/unstable";
+import type { SDKStartupFailureReason } from "@anthropic-ai/claude-agent-sdk";
+
+/** Makes the CLI write an `error_during_execution` result with a
+ *  `startup_failure_reason` before it exits on a known startup failure. Without
+ *  it, some failures (e.g. `proxy_invalid`) end with stderr and an exit code
+ *  alone. The SDK then rejects `initializationResult()` with an error that
+ *  carries the reason as `startupFailureReason`. */
+export const STARTUP_FAILURE_RESULTS_ENV = { CLAUDE_CODE_STARTUP_FAILURE_RESULTS: "1" };
+
+/** The SDK's prefix on the message of an error built from an error result. */
+const ERROR_RESULT_PREFIX = "Claude Code returned an error result: ";
+
+/** Reasons that signing in again, or with another account, can fix. */
+const AUTH_REQUIRED_REASONS: ReadonlySet<SDKStartupFailureReason> = new Set([
+  "gateway_signin_required",
+  "org_pin_mismatch",
+  "org_config_refused",
+]);
+
+/** The ACP error for a CLI that refused to start, or `undefined` when `error`
+ *  carries no `startupFailureReason` (older CLIs, failures without a known
+ *  cause). The message is the CLI's own, which says what to fix, e.g.
+ *  `Invalid proxy URL in HTTPS_PROXY: … Fix or unset HTTPS_PROXY and restart
+ *  Claude Code.`; `data.startupFailureReason` carries the reason. */
+export function startupFailureError(error: unknown): RequestError | undefined {
+  if (!(error instanceof Error)) return undefined;
+  const reason = (error as { startupFailureReason?: unknown }).startupFailureReason;
+  if (typeof reason !== "string" || reason === "") return undefined;
+
+  const message = error.message.startsWith(ERROR_RESULT_PREFIX)
+    ? error.message.slice(ERROR_RESULT_PREFIX.length)
+    : error.message;
+  const data = { startupFailureReason: reason };
+  if (AUTH_REQUIRED_REASONS.has(reason as SDKStartupFailureReason)) {
+    return RequestError.authRequired(data, message);
+  }
+  if (reason === "cwd_unavailable") {
+    return RequestError.invalidParams(data, message);
+  }
+  return RequestError.internalError(data, message);
+}
--- a/src/subagent-history.ts
+++ b/src/subagent-history.ts
@@ -24,6 +24,11 @@ export interface SubagentRecord {
  background: boolean;
  /** Whether the user stopped it. */
  stoppedByUser: boolean;
+  /**
+   * Its working directory, when Claude Code placed it outside its parent's:
+   * in a worktree of its own or of an ancestor, or in a `cwd` of its own.
+   */
+  cwd?: string;
 }

 /** Where the subagent transcripts of a session are. */
@@ -43,7 +48,9 @@ export interface SubagentHistory {
 * Claude keeps the history of a subagent in its own transcript,
 * `<session>/subagents/agent-<id>.jsonl`, next to the session transcript.
 * The `agent-<id>.meta.json` file beside it names the launching tool use.
- * The ids are empty for a session without a local transcript.
+ * For a child that Claude Code placed elsewhere, it has `worktreePath`,
+ * `inheritedWorktreePath` or `cwd`; then the child's working directory is the
+ * `cwd` of its transcript's records. The ids are empty for a session without a local transcript.
 */
 export async function subagentHistory(sessionId: string): Promise<SubagentHistory> {
  const agents = new Map<string, SubagentRecord>();
@@ -67,6 +74,12 @@ export async function subagentHistory(sessionId: string): Promise<SubagentHistor
        > | null;
        if (typeof meta?.toolUseId !== "string") return;
        const text = (value: unknown) => (typeof value === "string" ? value : undefined);
+        const placement = [meta.cwd, meta.worktreePath, meta.inheritedWorktreePath]
+          .map(text)
+          .find((value) => value && path.isAbsolute(value));
+        const cwd = placement
+          ? ((await recordedCwd(path.join(directory, `agent-${match[1]!}.jsonl`))) ?? placement)
+          : undefined;
        agents.set(meta.toolUseId, {
          agentId: match[1]!,
          name: text(meta.name),
@@ -74,6 +87,7 @@ export async function subagentHistory(sessionId: string): Promise<SubagentHistor
          description: text(meta.description),
          background: meta.requestShape === "background",
          stoppedByUser: meta.stoppedByUser === true,
+          ...(cwd ? { cwd } : {}),
        });
      } catch {
        // A damaged meta file leaves its subagent without history.
@@ -87,6 +101,31 @@ export async function subagentHistory(sessionId: string): Promise<SubagentHistor
  return dir ? { agents, dir } : { agents };
 }

+/**
+ * The `cwd` of the first record of the transcript `file` that has one, or
+ * undefined when the file cannot be read. Claude Code writes the working
+ * directory of the session or subagent on each record.
+ */
+async function recordedCwd(file: string): Promise<string | undefined> {
+  const stream = createReadStream(file, { encoding: "utf8" });
+  try {
+    for await (const line of readline.createInterface({ input: stream, crlfDelay: Infinity })) {
+      if (!line.includes('"cwd"')) continue;
+      try {
+        const cwd = (JSON.parse(line) as { cwd?: unknown } | null)?.cwd;
+        if (typeof cwd === "string" && path.isAbsolute(cwd)) return cwd;
+      } catch {
+        // A damaged record; a later one can have the `cwd`.
+      }
+    }
+  } catch {
+    // An unreadable transcript; the caller falls back to the metadata's path.
+  } finally {
+    stream.destroy();
+  }
+  return undefined;
+}
+
 /** The folder of the subagent transcripts, next to the session transcript `transcript`. */
 function subagentsDirectory(transcript: string, sessionId: string): string {
  return path.join(path.dirname(transcript), sessionId, "subagents");
@@ -162,6 +201,7 @@ export async function subagentLineage(
      agentId: current,
      launchId: launch.launchId,
      ...(launcher !== null ? { parentAgentId: launcher } : {}),
+      ...(launch.record.cwd ? { cwd: launch.record.cwd } : {}),
      ...(launch.record.name ? { name: launch.record.name } : {}),
      ...(launch.record.agentType ? { agentType: launch.record.agentType } : {}),
      ...(launch.record.description ? { description: launch.record.description } : {}),
--- a/src/subagent-replay.ts
+++ b/src/subagent-replay.ts
@@ -34,6 +34,7 @@
 */
 import type { SessionConfigOption } from "@agentclientprotocol/sdk/unstable";
 import type { SessionMessage } from "@anthropic-ai/claude-agent-sdk";
+import { statSync } from "node:fs";
 import type { AcpSessionNotification, SubagentState } from "./acp-subagents.js";
 import {
  childModelOption,
@@ -47,6 +48,7 @@ import {
  responseModelEntry,
  rfdEndState,
  rfdLabels,
+  sameDirectory,
  type SubagentModels,
  type WorkState,
 } from "./native-subagents.js";
@@ -71,6 +73,8 @@ export type ReplayChild = {
  /** The state of the child's last persisted task notification. */
  notified?: SubagentState;
  announced: boolean;
+  /** The `cwd` that the replay reported for it; undefined while it inherits its parent's. */
+  cwd?: string;
  promptSent: boolean;
  /** Whether it handed a report to its parent with a SubagentHandback call. */
  handedBack?: boolean;
@@ -118,6 +122,8 @@ export class RfdSubagentReplay {
     * {@link currentStates}, after the load response.
     */
    private readonly mapsDuringReplay = true,
+    /** The working directory of the root session, which a child inherits unless it reports its own. */
+    private readonly rootCwd?: string,
  ) {}

  /**
@@ -166,8 +172,9 @@ export class RfdSubagentReplay {

  /**
   * Announces `child` on its parent, as live: running, with the parent's
-   * labels. Then it sends `firstModel`, the model of the child's first
-   * response, when the transcript has one.
+   * labels, and with its recorded `cwd` when that differs from its parent's.
+   * Then it sends `firstModel`, the model of the child's first response, when
+   * the transcript has one.
   */
  async announce(child: ReplayChild, firstModel?: string): Promise<void> {
    if (child.announced) return;
@@ -176,6 +183,12 @@ export class RfdSubagentReplay {
      child.record.agentType ?? child.input.subagent_type,
      child.record.description ?? child.input.description,
    );
+    const inherited = this.effectiveCwd(child.parentSessionId);
+    const cwd =
+      child.record.cwd &&
+      (inherited === undefined || !(await sameDirectory(child.record.cwd, inherited)))
+        ? child.record.cwd
+        : undefined;
    await this.publish({
      sessionId: child.parentSessionId,
      update: {
@@ -183,13 +196,30 @@ export class RfdSubagentReplay {
        sessionId: child.sessionId,
        ...(labels.title ? { title: labels.title } : {}),
        ...(labels.description ? { description: labels.description } : {}),
+        ...(cwd ? { cwd } : {}),
        state: { state: "running" },
      },
    });
+    child.cwd = cwd;
    child.announced = true;
    await this.responseModel(child, firstModel);
  }

+  /**
+   * The working directory of the session `sessionId` as the client holds it:
+   * a child's reported `cwd`, else its parent's, up to the root's.
+   */
+  private effectiveCwd(sessionId: string): string | undefined {
+    const seen = new Set<string>();
+    let child = this.byAgentId.get(sessionId);
+    while (child && !seen.has(child.sessionId)) {
+      if (child.cwd) return child.cwd;
+      seen.add(child.sessionId);
+      child = this.byAgentId.get(child.parentSessionId);
+    }
+    return this.rootCwd;
+  }
+
  /**
   * Takes the model of a replayed response of the child `owner`. A child
   * whose model changes gets its `model` option again.
@@ -370,6 +400,10 @@ export class RfdSubagentReplay {
   * when a live session is loaded again. Such a child reports that state and
   * can be cancelled, as live. Any other child cannot be running, because the
   * process that ran it is gone, so its replayed end is its current state.
+   *
+   * A replayed `cwd` whose directory is gone, such as a worktree that Claude
+   * Code removed when the child finished, is cleared with `cwd: null`, as the
+   * RFD requires after a reconnection.
   */
  currentStates(
    live: (sessionId: string) => WorkState["state"] | undefined,
@@ -395,6 +429,7 @@ export class RfdSubagentReplay {
              sessionUpdate: "subagent_update",
              sessionId: child.sessionId,
              ...(liveState !== undefined ? { capabilities: { cancel: {} } } : {}),
+              ...(child.cwd && !isDirectory(child.cwd) ? { cwd: null } : {}),
              state,
            },
          },
@@ -574,6 +609,15 @@ function textOf(content: unknown): string {
    .join("\n");
 }

+/** Whether `dir` is an existing directory. */
+function isDirectory(dir: string): boolean {
+  try {
+    return statSync(dir).isDirectory();
+  } catch {
+    return false;
+  }
+}
+
 /** A message that a SendMessage call delivered to the child. */
 function isDelivery(message: SessionMessage): boolean {
  return (message as { origin?: { kind?: unknown } | null }).origin?.kind === "coordinator";
--- a/src/tests/acp-agent-settings.test.ts
+++ b/src/tests/acp-agent-settings.test.ts
@@ -42,6 +42,7 @@ describe("ClaudeAcpAgent settings", () => {
              value: "claude-sonnet-4-6",
              displayName: "Claude Sonnet 4.5",
              description: "Default",
+              supportsAutoMode: true,
            },
          ],
        }),
@@ -284,7 +285,7 @@ describe("ClaudeAcpAgent settings", () => {

  it("drops escalating defaultMode when it comes from project-tier settings", async () => {
    // bypassPermissions in .claude/settings.json (a repo-committed tier) is
-    // filtered by the SDK's trust policy and clamps to 'default'.
+    // filtered by the SDK's trust policy, so the built-in default applies.
    const projectDir = path.join(tempDir, "project");
    await fs.promises.mkdir(path.join(projectDir, ".claude"), { recursive: true });
    await fs.promises.writeFile(
@@ -303,8 +304,8 @@ describe("ClaudeAcpAgent settings", () => {
      _meta: { disableBuiltInTools: true },
    });

-    expect(getCapturedOptions().permissionMode).toBe("default");
-    expect(response.modes.currentModeId).toBe("default");
+    expect(getCapturedOptions().permissionMode).toBe("auto");
+    expect(response.modes.currentModeId).toBe("auto");
  });

  it("honors the host opt-out from bypassPermissions", async () => {
@@ -380,7 +381,7 @@ describe("ClaudeAcpAgent settings", () => {
    },
  );

-  it("defaults to 'default' when no permissions.defaultMode is set", async () => {
+  it("defaults to 'auto' when no permissions.defaultMode is set", async () => {
    const projectDir = path.join(tempDir, "project");
    await fs.promises.mkdir(projectDir, { recursive: true });

@@ -395,8 +396,37 @@ describe("ClaudeAcpAgent settings", () => {
      _meta: { disableBuiltInTools: true },
    });

-    expect(getCapturedOptions().permissionMode).toBe("default");
+    expect(getCapturedOptions().permissionMode).toBe("auto");
+    expect(response.modes.currentModeId).toBe("auto");
+  });
+
+  it.each([
+    { name: "top-level disableAutoMode", settings: { disableAutoMode: "disable" } },
+    {
+      name: "permissions.disableAutoMode with defaultMode 'auto'",
+      settings: { permissions: { disableAutoMode: "disable", defaultMode: "auto" } },
+    },
+  ])("starts in 'default' without Auto in the catalog for $name", async ({ settings }) => {
+    await fs.promises.writeFile(path.join(tempDir, "settings.json"), JSON.stringify(settings));
+    const projectDir = path.join(tempDir, "project");
+    await fs.promises.mkdir(projectDir, { recursive: true });
+
+    mockQuery();
+
+    const { ClaudeAcpAgent } = await import("../acp-agent.js");
+    const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+    (agent as any).logger = { log: () => {}, error: () => {} };
+
+    const response = await (agent as any).createSession({
+      cwd: projectDir,
+      mcpServers: [],
+      _meta: { disableBuiltInTools: true },
+    });
+
    expect(response.modes.currentModeId).toBe("default");
+    expect(response.modes.availableModes.map((mode: { id: string }) => mode.id)).not.toContain(
+      "auto",
+    );
  });

  describe("on resume", () => {
@@ -464,6 +494,16 @@ describe("ClaudeAcpAgent settings", () => {
      expect(response.modes.currentModeId).toBe("plan");
    });

+    it("uses the available configured mode when the restored mode is not in the catalog", async () => {
+      const { permissionMode, response } = await resume([user("dontAsk")]);
+
+      expect(permissionMode).toBe("plan");
+      expect(response.modes.currentModeId).toBe("plan");
+      expect(response.configOptions.find((option: any) => option.id === "mode").currentValue).toBe(
+        "plan",
+      );
+    });
+
    it("uses permissions.defaultMode when bypass is not available now", async () => {
      const { permissionMode, response } = await resume([user("bypassPermissions")], {
        claudeCode: { options: { allowDangerouslySkipPermissions: false } },
@@ -525,17 +565,18 @@ describe("ClaudeAcpAgent settings", () => {
        return createSession(params, options);
      };

-      await (agent as any).recreateSignedOutQuery(sessionId, (agent as any).sessions[sessionId]);
+      const husk = (agent as any).sessions[sessionId];
+      await (agent as any).recreateSignedOutQuery(sessionId, husk);

      expect(creations).toEqual([
-        { resume: sessionId, permissionMode: "default" },
-        { reuseSessionId: sessionId, permissionMode: "default" },
+        { resume: sessionId, permissionMode: "default", replacingSession: husk },
+        { reuseSessionId: sessionId, permissionMode: "default", replacingSession: husk },
      ]);
      expect(getCapturedOptions().permissionMode).toBe("default");
    });
  });

-  it("falls back to 'default' when permissions.defaultMode is invalid", async () => {
+  it("falls back to the built-in default when permissions.defaultMode is invalid", async () => {
    await fs.promises.writeFile(
      path.join(tempDir, "settings.json"),
      JSON.stringify({
@@ -559,9 +600,9 @@ describe("ClaudeAcpAgent settings", () => {
      _meta: { disableBuiltInTools: true },
    });

-    // Bad mode is ignored at the usage site; session creation must not throw.
-    expect(getCapturedOptions().permissionMode).toBe("default");
-    expect(response.modes.currentModeId).toBe("default");
+    // Settings resolution drops the bad mode; session creation must not throw.
+    expect(getCapturedOptions().permissionMode).toBe("auto");
+    expect(response.modes.currentModeId).toBe("auto");
  });

  it("ignores model from settings when it is not a string", async () => {
@@ -703,6 +744,30 @@ describe("ClaudeAcpAgent settings", () => {
      expect(modeIds).not.toContain("dontAsk");
    });

+    it("starts the built-in Auto default in Manual on an unsupported model", async () => {
+      const projectDir = path.join(tempDir, "project");
+      await fs.promises.mkdir(projectDir, { recursive: true });
+
+      const { setPermissionModeSpy } = mockQueryWithModels([
+        { value: "claude-haiku-4-5", displayName: "Claude Haiku", description: "Fast" },
+      ]);
+
+      const { ClaudeAcpAgent } = await import("../acp-agent.js");
+      const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+      const response = await (agent as any).createSession({
+        cwd: projectDir,
+        mcpServers: [],
+        _meta: { disableBuiltInTools: true },
+      });
+
+      expect(setPermissionModeSpy).toHaveBeenCalledWith("default");
+      expect(response.modes.currentModeId).toBe("default");
+      expect((agent as any).sessions[response.sessionId].autoModeFallbackWarningPending).toBe(
+        false,
+      );
+    });
+
    it("falls back permissions.defaultMode='auto' to Accept edits on an unsupported model", async () => {
      await fs.promises.writeFile(
        path.join(tempDir, "settings.json"),
--- a/src/tests/acp-agent.test.ts
+++ b/src/tests/acp-agent.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect, beforeAll, beforeEach, afterAll, afterEach, vi } from "vitest";
 import { spawn, spawnSync } from "child_process";
 import {
+  type AnyMessage,
  AvailableCommand,
  ClientCapabilities,
  client as acpClient,
@@ -41,7 +42,6 @@ import {
  isSyntheticLoginMessage,
  stripLocalCommandMetadata,
  ClaudeAcpAgent,
-  claudeCliPath,
  computeSessionFingerprint,
  streamEventToAcpNotifications,
  messageIdForGrouping,
@@ -55,9 +55,11 @@ import {
  type StreamedToolInputCache,
 } from "../acp-agent.js";
 import { SessionTitles } from "../session-titles.js";
+import { SessionBackgroundWork } from "../background-work.js";
 import { formatUsageResponse, isUsageCommandText, parseUsageResponse } from "../usage-markdown.js";
 import { Pushable } from "../utils.js";
-import { initializeClient, makeMockQuery } from "./helpers.js";
+import { heldRequest, initializeClient, makeMockQuery } from "./helpers.js";
+import { acpProtocolRouter } from "../serve.js";
 import * as agentSdk from "@anthropic-ai/claude-agent-sdk";
 import {
  deleteSession,
@@ -3548,11 +3550,20 @@ describe("session/list", () => {
    expect(second.sessions.map((session) => session.sessionId)).toEqual(["session-1000"]);
    expect(second.nextCursor).toBeUndefined();
    expect(vi.mocked(listSessions).mock.calls).toEqual([
-      [{ dir: "/workspace", limit: 1001, offset: 0 }],
-      [{ dir: "/workspace", limit: 1001, offset: 1000 }],
+      [{ dir: "/workspace", includeWorktrees: false, limit: 1001, offset: 0 }],
+      [{ dir: "/workspace", includeWorktrees: false, limit: 1001, offset: 1000 }],
    ]);
  });

+  it("rejects a relative cwd", async () => {
+    vi.mocked(listSessions).mockClear();
+    await expect(agent().listSessions({ cwd: "workspace" })).rejects.toMatchObject({
+      code: -32602,
+      data: { cwd: "workspace" },
+    });
+    expect(listSessions).not.toHaveBeenCalled();
+  });
+
  it("rejects a cursor that it did not issue", async () => {
    await expect(agent().listSessions({ cursor: "page-2" })).rejects.toThrow(
      "Unknown session/list cursor",
@@ -4006,7 +4017,8 @@ describe("subagent transcript replay", () => {
              return [
                ...response,
                `${on} subagent_update ${u.sessionId} ${JSON.stringify(u.state)}` +
-                  (u.capabilities ? ` capabilities=${JSON.stringify(u.capabilities)}` : ""),
+                  (u.capabilities ? ` capabilities=${JSON.stringify(u.capabilities)}` : "") +
+                  ("cwd" in u ? ` cwd=${JSON.stringify(u.cwd)}` : ""),
              ];
            case "session_message": {
              const references = [
@@ -4046,6 +4058,51 @@ describe("subagent transcript replay", () => {
      }
    }

+    it("announces a worktree child with its recorded cwd, and clears it when the worktree is gone", async () => {
+      const worktree = "/tmp/proj/.claude/worktrees/agent-wt1";
+      const trace = await replayRfd(
+        [
+          user("u1", "Go"),
+          assistant("a1", [
+            toolUse("toolu_wt", "Agent", { description: "Isolated", prompt: "Work apart" }),
+            toolUse("toolu_plain", "Agent", { description: "Shared", prompt: "Work here" }),
+          ]),
+          user("u2", [toolResult("toolu_wt", "Done."), toolResult("toolu_plain", "Done.")]),
+        ],
+        {
+          wt1: {
+            meta: {
+              agentType: "general-purpose",
+              toolUseId: "toolu_wt",
+              worktreePath: worktree,
+              spawnedWithWorktree: true,
+            },
+            records: [
+              user("w1", "Work apart", { cwd: worktree }),
+              assistant("w2", [{ type: "text", text: "Done." }], { cwd: worktree }),
+            ],
+          },
+          plain1: {
+            meta: { agentType: "general-purpose", toolUseId: "toolu_plain" },
+            records: [user("p1", "Work here"), assistant("p2", [{ type: "text", text: "Done." }])],
+          },
+        },
+        undefined,
+        { live: () => undefined },
+        { load: true },
+      );
+
+      expect(trace.filter((line) => line.includes(" subagent_update "))).toEqual([
+        `root subagent_update wt1 {"state":"running"} cwd="${worktree}"`,
+        'root subagent_update plain1 {"state":"running"}',
+        'root subagent_update plain1 {"state":"idle","stopReason":"end_turn"}',
+        'root subagent_update wt1 {"state":"idle","stopReason":"end_turn"}',
+        // After the response: the worktree no longer exists.
+        'root subagent_update wt1 {"state":"idle","stopReason":"end_turn"} cwd=null',
+        'root subagent_update plain1 {"state":"idle","stopReason":"end_turn"}',
+      ]);
+    });
+
    it("replays a fork child without the launching message and boilerplate it inherited", async () => {
      // A `subagent_type: "fork"` transcript starts with a copy of the
      // launching message (same API message id) and a directive message with
@@ -4716,6 +4773,58 @@ describe("escape markdown", () => {
  });
 });

+describe("request validation", () => {
+  function agent() {
+    return new ClaudeAcpAgent({ sessionUpdate: async () => {} } as unknown as AcpClient, {
+      log: () => {},
+      error: () => {},
+    });
+  }
+
+  it("rejects a session/new with a relative additional directory", async () => {
+    await expect(
+      agent().newSession({ cwd: os.tmpdir(), mcpServers: [], additionalDirectories: ["extra"] }),
+    ).rejects.toMatchObject({ code: -32602, data: { additionalDirectories: ["extra"] } });
+  });
+
+  it("rejects authenticate with an unknown method id", async () => {
+    await expect(agent().authenticate({ methodId: "unknown-method" })).rejects.toMatchObject({
+      code: -32602,
+      data: { methodId: "unknown-method" },
+    });
+  });
+
+  it("rejects a v1 prompt with audio before it looks up the session", async () => {
+    // An unknown session would fail with -32002 if the check ran later.
+    await expect(
+      agent().prompt({
+        sessionId: "unknown-session",
+        prompt: [
+          { type: "text", text: "listen" },
+          { type: "audio", data: "AAAA", mimeType: "audio/wav" },
+        ],
+      }),
+    ).rejects.toMatchObject({ code: -32602, data: { type: "audio" } });
+  });
+
+  it("drops slash commands whose name has whitespace, and repeats of a name", async () => {
+    const a = agent();
+    const supportedCommands = async () => [
+      { name: "review", description: "first" },
+      { name: "review", description: "second" },
+      { name: "my command", description: "spaced" },
+      { name: "compact", description: "Compact the conversation" },
+    ];
+    a.sessions["test-session"] = mockSessionState({ query: { supportedCommands } }, a) as any;
+    const commands = await a.availableCommands("test-session");
+    expect(commands.map((command) => [command.name, command.description])).toEqual([
+      ["review", "first"],
+      ["compact", "Compact the conversation"],
+      ["mcp", expect.any(String)],
+    ]);
+  });
+});
+
 describe("prompt conversion", () => {
  it("should not change built-in slash commands", () => {
    const message = promptToClaude({
@@ -4753,6 +4862,22 @@ describe("prompt conversion", () => {
    ]);
  });

+  it("rewrites an MCP slash command with multi-line input, in the first text block only", () => {
+    const message = promptToClaude({
+      sessionId: "test",
+      prompt: [
+        { type: "resource_link", uri: "file:///work/a.ts", name: "a.ts" },
+        { type: "text", text: "/mcp:server:name first line\nsecond line" },
+        { type: "text", text: "/mcp:server:other args" },
+      ],
+    });
+    expect(message.message.content).toEqual([
+      { type: "text", text: "[@a.ts](file:///work/a.ts)" },
+      { type: "text", text: "/server:name (MCP) first line\nsecond line" },
+      { type: "text", text: "/mcp:server:other args" },
+    ]);
+  });
+
  it("sends image, PDF and text blob resources to Claude, and skips other blobs", () => {
    const blob = (uri: string, mimeType: string, data: string) => ({
      type: "resource" as const,
@@ -4810,11 +4935,6 @@ describe("prompt conversion", () => {
 });

 describe.skipIf(!process.env.RUN_INTEGRATION_TESTS)("SDK behavior", () => {
-  it("finds vendored cli path", async () => {
-    const path = await claudeCliPath();
-    expect(path).toMatch(/@anthropic-ai\/claude-agent-sdk-[^/]+\/claude(\.exe)?$/);
-  });
-
  it("query has a 'default' model", async () => {
    const q = query({ prompt: "hi" });
    const models = await q.supportedModels();
@@ -5076,6 +5196,7 @@ describe("permission request cancellation", () => {
      toolUseCache: {},
      emittedToolCalls: new Set(),
      liveBackgroundTasks: new Map(),
+      background: new SessionBackgroundWork(sessionId, false),
      emittedAssistantText: false,
      owedTrailingIdles: 0,
      messageIdToUuid: new Map(),
@@ -5114,10 +5235,11 @@ describe("permission request cancellation", () => {
    // Let canUseTool reach the awaited requestPermission before cancelling.
    await Promise.resolve();

-    // The tool-call signal is threaded through as the cancellation signal.
-    expect(receivedSignal).toBe(controller.signal);
+    // The cancellation signal follows the tool-call signal.
+    expect(receivedSignal?.aborted).toBe(false);

    controller.abort();
+    expect(receivedSignal?.aborted).toBe(true);

    await expect(pending).rejects.toThrow("Tool use aborted");
  });
@@ -5125,7 +5247,7 @@ describe("permission request cancellation", () => {
  it("does not wait for a permission client that ignores cancellation", async () => {
    const mockClient = {
      sessionUpdate: async () => {},
-      requestPermission: () => new Promise<RequestPermissionResponse>(() => {}),
+      requestPermission: heldRequest<RequestPermissionResponse>,
    } as unknown as AcpClient;
    const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
    const session = injectSession(agent, "session-1");
@@ -5144,14 +5266,14 @@ describe("permission request cancellation", () => {
  });

  describe("a cancelled outcome", () => {
-    function setup() {
+    function setup(options: { v2?: boolean } = {}) {
      const mockClient = {
        sessionUpdate: async () => {},
        requestPermission: async (): Promise<RequestPermissionResponse> => ({
          outcome: { outcome: "cancelled" },
        }),
      } as unknown as AcpClient;
-      const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
+      const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} }, options);
      const session = injectSession(agent, "session-1");
      session.emittedToolCalls.add("tool-1");
      const ask = (agentID?: string) =>
@@ -5173,6 +5295,29 @@ describe("permission request cancellation", () => {
      await expect(ask("agent-fg")).rejects.toThrow("Tool use aborted");
    });

+    it("denies the tool use of foreground work on v2 without a session/cancel", async () => {
+      // On v2 the client also answers `cancelled` when the user dismissed the
+      // prompt or its policy declined it. The turn goes on without the tool.
+      const { session, ask } = setup({ v2: true });
+      session.liveBackgroundTasks.set("agent-fg", { isSubagent: true });
+
+      for (const agentID of [undefined, "agent-fg"]) {
+        await expect(ask(agentID)).resolves.toEqual({
+          behavior: "deny",
+          message: "User refused permission to run tool",
+          toolUseID: "tool-1",
+          decisionClassification: "user_reject",
+        });
+      }
+    });
+
+    it("aborts the tool use of foreground work on v2 during a session/cancel", async () => {
+      const { session, ask } = setup({ v2: true });
+      session.cancelled = true;
+
+      await expect(ask()).rejects.toThrow("Tool use aborted");
+    });
+
    it("denies the tool use of a background subagent", async () => {
      const { session, ask } = setup();
      session.liveBackgroundTasks.set("agent-bg", { isSubagent: true, backgrounded: true });
@@ -5252,7 +5397,7 @@ describe("permission request cancellation", () => {
    "does not wait for $name when its client ignores cancellation",
    async ({ start, aborted }) => {
      // The client holds the elicitation and never answers $/cancel_request.
-      const createElicitation = vi.fn(() => new Promise<CreateElicitationResponse>(() => {}));
+      const createElicitation = vi.fn(heldRequest<CreateElicitationResponse>);
      const mockClient = {
        sessionUpdate: async () => {},
        createElicitation,
@@ -5265,39 +5410,129 @@ describe("permission request cancellation", () => {
      const controller = new AbortController();
      const pending = start(agent, controller.signal);
      await vi.waitFor(() => expect(createElicitation).toHaveBeenCalledOnce());
-      // The client was asked to cancel the request, and ignores that.
-      expect(createElicitation.mock.calls[0]).toEqual([expect.anything(), controller.signal]);
+      const [, requestSignal] = createElicitation.mock.calls[0] as unknown as [
+        unknown,
+        AbortSignal,
+      ];
      controller.abort();
+      // The client was asked to cancel the request, and ignores that.
+      expect(requestSignal.aborted).toBe(true);

      await aborted(pending);
      expect(session.openUserInputs?.size ?? 0).toBe(0);
    },
  );

-  it("observes a client rejection when the signal aborts during request creation", async () => {
-    const controller = new AbortController();
-    const clientOperation = Promise.reject(new Error("Request cancelled"));
-    const then = vi.spyOn(clientOperation, "then");
+  it.each(elicitations)(
+    "cancels $name before session/close responds",
+    async ({ start, aborted }) => {
+      const events: string[] = [];
+      const createElicitation = vi.fn((params: unknown, signal: AbortSignal) => {
+        signal.addEventListener("abort", () => events.push("cancel_request"), { once: true });
+        return heldRequest<CreateElicitationResponse>(params, signal);
+      });
+      const mockClient = {
+        sessionUpdate: async () => {},
+        createElicitation,
+      } as unknown as AcpClient;
+      const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
+      await initializeClient(agent, { elicitation: { form: {}, url: {} } });
+      const session = injectSession(agent, "session-1");
+      session.emittedToolCalls.add("tool-1");
+
+      // Claude Code's own signal for the callback never aborts here.
+      const pending = start(agent, new AbortController().signal);
+      await vi.waitFor(() => expect(createElicitation).toHaveBeenCalledOnce());
+      await agent.closeSession({ sessionId: "session-1" });
+      events.push("closed");
+
+      expect(events).toEqual(["cancel_request", "closed"]);
+      await aborted(pending);
+    },
+  );
+
+  it.each([
+    {
+      name: "a permission request",
+      start: (agent: ClaudeAcpAgent, signal: AbortSignal) =>
+        agent.canUseTool("session-1")("Bash", { command: "ls" }, {
+          signal,
+          suggestions: [],
+          toolUseID: "tool-1",
+        } as any),
+    },
+    elicitations[0],
+  ])(
+    "cancels $name over the connection and stops waiting for a client that ignores it",
+    async ({ start }) => {
+      const toAgent = new TransformStream<AnyMessage, AnyMessage>();
+      const toClient = new TransformStream<AnyMessage, AnyMessage>();
+      let agent!: ClaudeAcpAgent;
+      acpProtocolRouter(
+        { log: () => {}, error: () => {} },
+        (created) => (agent = created),
+        "v1",
+      ).connect({ readable: toAgent.readable, writable: toClient.writable });
+      const cancelled: string[] = [];
+      // The client holds each request. The signal also aborts when the
+      // connection closes, with another reason than `-32800`.
+      const hold = ({ method, signal }: { method: string; signal: AbortSignal }) =>
+        new Promise<never>(() => {
+          signal.addEventListener("abort", () => {
+            if ((signal.reason as { code?: unknown } | undefined)?.code === -32800) {
+              cancelled.push(method);
+            }
+          });
+        });
+
+      await acpClient({ name: "test-client" })
+        .onRequest(methods.client.session.requestPermission, hold)
+        .onRequest(methods.client.elicitation.create, hold)
+        .connectWith(
+          { readable: toClient.readable, writable: toAgent.writable },
+          async (client) => {
+            await client.request(methods.agent.initialize, {
+              protocolVersion: 1,
+              clientCapabilities: { elicitation: { form: {} } },
+            });
+            const session = injectSession(agent, "session-1");
+            session.emittedToolCalls.add("tool-1");
+            const controller = new AbortController();
+            const pending = start(agent, controller.signal);
+            await vi.waitFor(() => expect(session.openUserInputs?.size).toBe(1));
+            controller.abort();
+
+            await expect(pending).rejects.toThrow("Tool use aborted");
+            await vi.waitFor(() => expect(cancelled).toHaveLength(1));
+          },
+        );
+    },
+  );
+
+  it("cancels a permission request before session/close responds", async () => {
+    const events: string[] = [];
    const mockClient = {
      sessionUpdate: async () => {},
-      requestPermission: () => {
-        controller.abort();
-        return clientOperation;
+      requestPermission: (params: RequestPermissionRequest, signal?: AbortSignal) => {
+        signal?.addEventListener("abort", () => events.push("cancel_request"), { once: true });
+        return heldRequest<RequestPermissionResponse>(params, signal);
      },
    } as unknown as AcpClient;
    const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
    const session = injectSession(agent, "session-1");
    session.emittedToolCalls.add("tool-1");

-    await expect(
-      agent.canUseTool("session-1")("Bash", { command: "ls" }, {
-        signal: controller.signal,
-        suggestions: [],
-        toolUseID: "tool-1",
-      } as any),
-    ).rejects.toThrow("Tool use aborted");
+    const pending = agent.canUseTool("session-1")("Bash", { command: "ls" }, {
+      signal: new AbortController().signal,
+      suggestions: [],
+      toolUseID: "tool-1",
+    } as any);
+    await vi.waitFor(() => expect(session.openUserInputs?.size).toBe(1));
+    await agent.closeSession({ sessionId: "session-1" });
+    events.push("closed");

-    expect(then).toHaveBeenCalledOnce();
+    expect(events).toEqual(["cancel_request", "closed"]);
+    await expect(pending).rejects.toThrow("Tool use aborted");
  });

  it("does not wait for an eager tool-call update that ignores cancellation", async () => {
@@ -6592,7 +6827,7 @@ describe("subagent permission attribution (issue #851)", () => {
          sessionUpdate: async (notification: AcpSessionNotification) => {
            updates.push(notification);
          },
-          requestPermission: () => new Promise(() => {}),
+          requestPermission: heldRequest,
        } as unknown as AcpClient,
        { log: () => {}, error: () => {} },
      );
@@ -7129,7 +7364,7 @@ describe("subagent permission attribution (issue #851)", () => {
          updates.push(notification);
        },
        // A client that ignores $/cancel_request.
-        createElicitation: () => new Promise(() => {}),
+        createElicitation: heldRequest,
      } as unknown as AcpClient,
      { log: () => {}, error: () => {} },
    );
@@ -8425,7 +8660,7 @@ describe("subagent permission attribution (issue #851)", () => {
          requestPermission: (params: { sessionId: string }, signal?: AbortSignal) => {
            log.push(`request @${params.sessionId}`);
            signal?.addEventListener("abort", () => log.push(`withdrawn @${params.sessionId}`));
-            return new Promise(() => {});
+            return heldRequest(params, signal);
          },
        } as unknown as AcpClient,
        { log: () => {}, error: () => {} },
@@ -14388,6 +14623,8 @@ describe("session/fork", () => {
      { sessionUpdate: async (n: SessionNotification) => updates.push(n) } as unknown as AcpClient,
      { log: () => {}, error: () => {} },
    );
+    // The scripted sessions run in a cwd that does not exist here.
+    vi.spyOn(agent as any, "validateCwd").mockResolvedValue(undefined);
    const createSession = vi
      .spyOn(agent as any, "createSession")
      .mockImplementation(async (params: any, options: any) => {
@@ -14484,6 +14721,35 @@ describe("session/fork", () => {
    ).rejects.toThrow("Claude Code did not start");
  });

+  it("rejects a bad cwd or a relative additional directory before copying the transcript", async () => {
+    const { agent, createSession } = forkingAgent();
+    (agent as any).validateCwd.mockRestore();
+    const missing = path.join(os.tmpdir(), `missing-${randomUUID()}`);
+
+    for (const params of [
+      { cwd: "workspace" },
+      { cwd: missing },
+      { cwd: os.tmpdir(), additionalDirectories: ["extra"] },
+    ]) {
+      await expect(
+        agent.unstable_forkSession({ sessionId: "source-id", mcpServers: [], ...params }),
+      ).rejects.toMatchObject({ code: -32602 });
+    }
+    expect(forkSession).not.toHaveBeenCalled();
+    expect(createSession).not.toHaveBeenCalled();
+  });
+
+  it("reports an unknown source session as not found", async () => {
+    const { agent, createSession } = forkingAgent();
+    // What the Claude SDK `forkSession` throws for a session without a transcript.
+    vi.mocked(forkSession).mockRejectedValueOnce(new Error("Session source-id not found"));
+
+    await expect(
+      agent.unstable_forkSession({ sessionId: "source-id", cwd: "/workspace", mcpServers: [] }),
+    ).rejects.toMatchObject({ code: -32002, data: { sessionId: "source-id" } });
+    expect(createSession).not.toHaveBeenCalled();
+  });
+
  it("forks the latest turn in the requested workspace", async () => {
    const { agent, createSession } = forkingAgent();
    vi.mocked(forkSession).mockResolvedValueOnce({ sessionId: "fork-id" });
@@ -14728,6 +14994,7 @@ describe("session/close", () => {
      toolUseCache: {},
      emittedToolCalls: new Set(),
      liveBackgroundTasks: new Map(),
+      background: new SessionBackgroundWork(sessionId, false),
      emittedAssistantText: false,
      owedTrailingIdles: 0,
      messageIdToUuid: new Map(),
@@ -14850,6 +15117,7 @@ describe("session/delete", () => {
      toolUseCache: {},
      emittedToolCalls: new Set(),
      liveBackgroundTasks: new Map(),
+      background: new SessionBackgroundWork(sessionId, false),
      emittedAssistantText: false,
      owedTrailingIdles: 0,
      messageIdToUuid: new Map(),
@@ -14945,7 +15213,10 @@ describe("getOrCreateSession param change detection", () => {
    const mockClient = {
      sessionUpdate: async () => {},
    } as unknown as AcpClient;
-    return new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
+    const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
+    // The injected sessions run in cwds that do not exist here, such as "/test".
+    vi.spyOn(agent as any, "validateCwd").mockResolvedValue(undefined);
+    return agent;
  }

  function injectSession(
@@ -15010,6 +15281,7 @@ describe("getOrCreateSession param change detection", () => {
      toolUseCache: {},
      emittedToolCalls: new Set(),
      liveBackgroundTasks: new Map(),
+      background: new SessionBackgroundWork(sessionId, false),
      emittedAssistantText: false,
      owedTrailingIdles: 0,
      messageIdToUuid: new Map(),
@@ -15061,6 +15333,32 @@ describe("getOrCreateSession param change detection", () => {
    );
  });

+  it("keeps the live session when a resume or load names a bad cwd or additional directory", async () => {
+    const agent = createMockAgent();
+    (agent as any).validateCwd.mockRestore();
+    const session = injectSession(agent, "s1", { cwd: "/old" });
+    const createSessionSpy = vi.spyOn(agent as any, "createSession");
+    const missing = path.join(os.tmpdir(), `missing-${randomUUID()}`);
+
+    for (const params of [
+      { cwd: "relative" },
+      { cwd: missing },
+      { cwd: os.tmpdir(), additionalDirectories: ["extra"] },
+    ]) {
+      await expect(
+        agent.resumeSession({ sessionId: "s1", mcpServers: [], ...params }),
+      ).rejects.toMatchObject({ code: -32602 });
+    }
+    vi.mocked(getSessionMessages).mockResolvedValueOnce([]);
+    await expect(
+      agent.loadSession({ sessionId: "s1", cwd: missing, mcpServers: [] }),
+    ).rejects.toMatchObject({ code: -32602 });
+
+    expect(agent.sessions["s1"]).toBe(session);
+    expect(session.abortController.signal.aborted).toBe(false);
+    expect(createSessionSpy).not.toHaveBeenCalled();
+  });
+
  // Claude Code writes the conversation at the first prompt, so a live session
  // that was never prompted has nothing to resume.
  it("starts a fresh query under the same id for a live session that was never prompted", async () => {
@@ -18556,6 +18854,38 @@ describe("assembled assistant text fallback", () => {
    });
  });

+  it("logs session_writes_lost after the last result without sending an update", async () => {
+    const updates: any[] = [];
+    const error = vi.fn();
+    const agent = new ClaudeAcpAgent(
+      { sessionUpdate: async (n: any) => updates.push(n) } as unknown as AcpClient,
+      { log: () => {}, error },
+    );
+    injectSession(agent, [
+      replayedResult("done"),
+      idle,
+      {
+        type: "system",
+        subtype: "session_writes_lost",
+        error_code: "ENOSPC",
+        lost: ["transcript", "global_config"],
+        transcript_session_ids: ["test-session"],
+        uuid: randomUUID(),
+        session_id: "test-session",
+      },
+    ]);
+
+    await agent.prompt({ sessionId: "test-session", prompt: [{ type: "text", text: "1+2" }] });
+    const sentAtTurnEnd = updates.length;
+
+    await vi.waitFor(() =>
+      expect(error).toHaveBeenCalledWith(
+        "Session test-session: Claude Code could not save transcript and global_config (ENOSPC); resuming may miss part of the conversation",
+      ),
+    );
+    expect(updates).toHaveLength(sentAtTurnEnd);
+  });
+
  it("marks info-level notices even when their text has no severity prefix", async () => {
    const { agent, updates } = createMockAgentWithCapture();
    injectSession(agent, [
@@ -19465,6 +19795,7 @@ describe("post-error recovery", () => {
      toolUseCache: {},
      emittedToolCalls: new Set(),
      liveBackgroundTasks: new Map(),
+      background: new SessionBackgroundWork("test-session", false),
      emittedAssistantText: false,
      owedTrailingIdles: 0,
      messageIdToUuid: new Map(),
@@ -19989,6 +20320,72 @@ describe("post-error recovery", () => {
    await agent.sessions["test-session"]?.consumer;
  });

+  it("does not cancel a prompt received while the cancel awaits", async () => {
+    // Turn 1 runs and turn 2 is queued when the cancel arrives. Turn 3 arrives
+    // while the cancel awaits `contextCompaction.interrupt()`: ACP v2 cancels
+    // only prompts received before `session/cancel`, so turn 3 must run.
+    const agent = createMockAgent();
+    let releaseInterrupt!: () => void;
+    const interruptGate = new Promise<void>((resolve) => (releaseInterrupt = resolve));
+    let releaseStream!: () => void;
+    const streamGate = new Promise<void>((resolve) => (releaseStream = resolve));
+    const orphanResult = createResultMessage({
+      subtype: "success",
+      stop_reason: "end_turn",
+      is_error: false,
+    });
+    injectGeneratorSession(
+      agent,
+      (input) => {
+        async function* messageGenerator() {
+          const iter = input[Symbol.asyncIterator]();
+          const u1 = await iter.next();
+          yield userEcho(u1.value); // turn 1 active
+          await iter.next(); // turn 2, queued before the cancel
+          const u3 = await iter.next(); // turn 3, queued during the cancel
+          await streamGate;
+          yield { type: "system", subtype: "session_state_changed", state: "idle" }; // turn 1 cancelled
+          yield orphanResult; // turn 2's result, skipped as an orphan
+          yield userEcho(u3.value);
+          yield createResultMessage({
+            subtype: "success",
+            stop_reason: "end_turn",
+            is_error: false,
+          });
+          yield { type: "system", subtype: "session_state_changed", state: "idle" };
+        }
+        return messageGenerator();
+      },
+      { contextCompaction: { interrupt: () => interruptGate } },
+    );
+
+    const first = agent.prompt({
+      sessionId: "test-session",
+      prompt: [{ type: "text", text: "first" }],
+    });
+    await waitFor(() => !!agent.sessions["test-session"]?.activeTurn);
+    const second = agent.prompt({
+      sessionId: "test-session",
+      prompt: [{ type: "text", text: "second" }],
+    });
+    await waitFor(() => (agent.sessions["test-session"]?.turnQueue?.length ?? 0) >= 2);
+
+    const cancel = agent.cancel({ sessionId: "test-session" });
+    const third = agent.prompt({
+      sessionId: "test-session",
+      prompt: [{ type: "text", text: "third" }],
+    });
+    await waitFor(() => (agent.sessions["test-session"]?.turnQueue?.length ?? 0) >= 3);
+    releaseInterrupt();
+    await cancel;
+    releaseStream();
+
+    await expect(first).resolves.toMatchObject({ stopReason: "cancelled" });
+    await expect(second).resolves.toEqual({ stopReason: "cancelled" });
+    await expect(third).resolves.toMatchObject({ stopReason: "end_turn" });
+    await agent.sessions["test-session"]?.consumer;
+  });
+
  it("drains the orphan count, then promotes a no-echo /compact while still cancelled", async () => {
    // The case that ONLY the orphan-count gate handles (the old `!cancelled`
    // gate would hang it): cancel removes a queued turn (count=1), its orphan
@@ -21846,7 +22243,7 @@ describe("output after a cancel", () => {
    expect(texts).toEqual(["Starting the build.", "The build", " passed."]);
  });

-  it("drops the answer to a prompt sent while the cancel was still in progress", async () => {
+  it("answers a prompt sent while the cancel was still in progress", async () => {
    const interrupting = Promise.withResolvers<void>();
    const release = Promise.withResolvers<void>();
    const cancelDone = Promise.withResolvers<void>();
@@ -21895,14 +22292,20 @@ describe("output after a cancel", () => {
    await cancelling;
    cancelDone.resolve();

+    // The cancel covers only the prompts received before it.
    await expect(first).resolves.toMatchObject({ stopReason: "cancelled" });
-    await expect(second).resolves.toEqual({ stopReason: "cancelled" });
+    await expect(second).resolves.toMatchObject({ stopReason: "end_turn" });
    await consumer;
-    expect(texts).toEqual(["Starting the build.", "The build", " passed."]);
+    expect(texts).toEqual([
+      "Starting the build.",
+      "Here is the second answer.",
+      "The build",
+      " passed.",
+    ]);
    expect(session.lastTurnFailed).not.toBe(true);
  });

-  it("drops the answer to a prompt sent during the cancel whose request comes before the cancel abandons it", async () => {
+  it("answers a prompt sent during the cancel that Claude Code takes before the cancel ends", async () => {
    const interrupting = Promise.withResolvers<void>();
    const release = Promise.withResolvers<void>();
    const requested = Promise.withResolvers<void>();
@@ -21955,10 +22358,16 @@ describe("output after a cancel", () => {
    await cancelling;
    swept.resolve();

+    // The cancel covers only the prompts received before it.
    await expect(first).resolves.toMatchObject({ stopReason: "cancelled" });
-    await expect(second).resolves.toEqual({ stopReason: "cancelled" });
+    await expect(second).resolves.toMatchObject({ stopReason: "end_turn" });
    await consumer;
-    expect(texts).toEqual(["Starting the build.", "The build", " passed."]);
+    expect(texts).toEqual([
+      "Starting the build.",
+      "Here is the second answer.",
+      "The build",
+      " passed.",
+    ]);
  });

  it("keeps the prompts an earlier cancel stopped when the user cancels again", async () => {
@@ -26538,7 +26947,7 @@ describe("turn steering (_session/steering)", () => {
    "uses priority:'now' again once $name is withdrawn, though its client never settles it",
    async ({ start }) => {
      // A client that ignores $/cancel_request: its request never settles.
-      const userInputRequest = vi.fn(() => new Promise<never>(() => {}));
+      const userInputRequest = vi.fn(heldRequest<never>);
      const input = new Pushable<any>();
      const inputPush = vi.spyOn(input, "push");
      const agent = new ClaudeAcpAgent(
@@ -27822,6 +28231,7 @@ describe("session/cancel wedge recovery (issue #680)", () => {
      toolUseCache: {},
      emittedToolCalls: new Set(),
      liveBackgroundTasks: new Map(),
+      background: new SessionBackgroundWork("test-session", false),
      emittedAssistantText: false,
      owedTrailingIdles: 0,
      messageIdToUuid: new Map(),
@@ -29730,6 +30140,7 @@ describe("agent selection config option", () => {
        toolUseCache: {},
        emittedToolCalls: new Set(),
        liveBackgroundTasks: new Map(),
+        background: new SessionBackgroundWork(sessionId, false),
        emittedAssistantText: false,
        owedTrailingIdles: 0,
        messageIdToUuid: new Map(),
--- a/src/tests/acp-scenarios/snapshots/air/session-load-replay.jsonl
+++ b/src/tests/acp-scenarios/snapshots/air/session-load-replay.jsonl
@@ -12,6 +12,6 @@
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>:replay-subagent:toolu_r_task","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_r_task"}},"content":{"text":"Subagent text.","type":"text"},"messageId":"msg_r_sub","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"content":{"text":"Fixed.","type":"text"},"messageId":"msg_r2","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"sessionUpdate":"subagent_state_update","state":"completed","subagentSessionId":"<session>:replay-subagent:toolu_r_task"}}}
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 {"kind":"sessionUpdate","payload":{"sessionId":"<session>:replay-subagent:toolu_r_task","update":{"configOptions":[{"category":"model","currentValue":"claude-sonnet-4-6","id":"model","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]"},"name":"mcp"}],"sessionUpdate":"available_commands_update"}}}
--- a/src/tests/acp-scenarios/snapshots/air/session-setup.jsonl
+++ b/src/tests/acp-scenarios/snapshots/air/session-setup.jsonl
@@ -1,3 +1,3 @@
 {"kind":"initialize","payload":{"_meta":{"jetbrains":{"air":{"capabilities":["sessionFailure","agentFileChangeReport","nativeSubagentSessions","asyncTasks","customInstructions","recommendedValue","diffPatch","planFile","backgroundSubagents"],"goal":{"actions":["set","clear"],"controlMethod":"_session/goal","version":1},"version":1}},"steering":{"supported":true}},"agentCapabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"auth":{"logout":{}},"loadSession":true,"mcpCapabilities":{"http":true,"sse":true},"promptCapabilities":{"embeddedContext":true,"image":true},"providers":{},"sessionCapabilities":{"additionalDirectories":{},"close":{},"delete":{},"fork":{},"list":{},"resume":{},"subagents":{},"systemPrompt":{"mode":{"override":{}}}}},"agentInfo":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"authMethods":[],"protocolVersion":1}}
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 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]"},"name":"mcp"}],"sessionUpdate":"available_commands_update"}}}
--- a/src/tests/acp-scenarios/snapshots/v2/ask-user-question.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/ask-user-question.jsonl
@@ -1,15 +1,15 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
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+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"other","name":"AskUserQuestion","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Asking for your input","toolCallId":"toolu_ask"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"Which database?","type":"text"},"type":"content"}],"rawInput":{"questions":[{"header":"Database","multiSelect":false,"options":[{"description":"Relational","label":"Postgres","preview":"CREATE TABLE t ();"},{"description":"Key-value","label":"Redis"}],"question":"Which database?"}]},"sessionUpdate":"tool_call_update","title":"Which database?","toolCallId":"toolu_ask"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"elicitation/create","payload":{"message":"Which database?","mode":"form","requestedSchema":{"properties":{"question_0":{"oneOf":[{"_meta":{"_claude/askUserQuestionOption":{"preview":"CREATE TABLE t ();"}},"const":"Postgres","description":"Relational","title":"Postgres"},{"const":"Redis","description":"Key-value","title":"Redis"}],"title":"Database","type":"string"},"question_0_custom":{"description":"Type your own answer, or add a note to the option you chose above (optional).","title":"Other","type":"string"}},"type":"object"},"sessionId":"<session>","toolCallId":"toolu_ask"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"User has answered your questions: \"Which database?\"=\"Postgres\".","type":"text"},"type":"content"}],"rawOutput":"User has answered your questions: \"Which database?\"=\"Postgres\".","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_ask"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
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+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/async-task-ends-before-tool-id.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/async-task-ends-before-tool-id.jsonl
@@ -1,6 +1,6 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/async-task-held-until-tool-id.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/async-task-held-until-tool-id.jsonl
@@ -1,6 +1,6 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
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+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/async-task-released-at-turn-end.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/async-task-released-at-turn-end.jsonl
@@ -1,6 +1,6 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
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+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/bash-background.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/bash-background.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"terminal_update","terminalId":"toolu_bg"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"terminalId":"toolu_bg","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Terminal","toolCallId":"toolu_bg"}}}
@@ -15,4 +15,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"exitStatus":{},"sessionUpdate":"terminal_update","terminalId":"toolu_bg"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_bg"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/bash-error.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/bash-error.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"terminal_update","terminalId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"terminalId":"toolu_bash","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Terminal","toolCallId":"toolu_bash"}}}
@@ -14,4 +14,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"exitStatus":{"exitCode":1},"sessionUpdate":"terminal_update","terminalId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"tool_call_update","status":"failed","toolCallId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/bash-foreground.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/bash-foreground.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"terminal_update","terminalId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"terminalId":"toolu_bash","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Terminal","toolCallId":"toolu_bash"}}}
@@ -10,9 +10,9 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"command":"ls -la"},"sessionUpdate":"tool_call_update","title":"ls -la","toolCallId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"command":"ls -la","description":"List files"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_bash"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"terminalId":"toolu_bash","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{"command":"ls -la","description":"List files"},"title":"ls -la","toolCallId":"toolu_bash"},"type":"tool_call"},"title":"ls -la"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"output":{"data":"YS50cwpiLnRz"},"sessionUpdate":"terminal_update","terminalId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"exitStatus":{"exitCode":0},"sessionUpdate":"terminal_update","terminalId":"toolu_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_bash"}}}
@@ -20,4 +20,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"ne.","type":"text"},"messageId":"msg_done","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/compaction-failed-legacy.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/compaction-failed-legacy.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","sessionUpdate":"compaction_update","status":"in_progress"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","error":"Context too small","sessionUpdate":"compaction_update","status":"failed"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/compaction-legacy.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/compaction-legacy.jsonl
@@ -1,11 +1,11 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","sessionUpdate":"compaction_update","status":"in_progress"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","content":{"text":"The summary.","type":"text"},"sessionUpdate":"compaction_summary_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","sessionUpdate":"compaction_update","status":"completed"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"usage_update","size":200000,"used":100}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":100}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/compaction-update.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/compaction-update.jsonl
@@ -1,11 +1,11 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","sessionUpdate":"compaction_update","status":"in_progress"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","content":{"text":"The summary.","type":"text"},"sessionUpdate":"compaction_summary_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"compactionId":"00000000-0000-4000-8000-000000000001","sessionUpdate":"compaction_update","status":"completed"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"usage_update","size":200000,"used":100}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":100}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/edit-rejected.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/edit-rejected.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"edit","locations":[],"name":"Edit","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Edit","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"path":"<cwd>/src/app.ts"}],"rawInput":{"file_path":"<cwd>/src/app.ts"},"sessionUpdate":"tool_call_update","title":"Edit src/app.ts","toolCallId":"toolu_edit"}}}
@@ -10,9 +10,9 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"file_path":"<cwd>/src/app.ts","new_string":"value = 2","old_string":"value = 1"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"changes":[{"fileType":"text","operation":"modify","path":"<cwd>/src/app.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/src/app.ts <cwd>/src/app.ts\n--- <cwd>/src/app.ts\n+++ <cwd>/src/app.ts\n@@ -1 +1 @@\n-const value = 1;\n+const value = 2;\n"},"type":"diff"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_edit"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"changes":[{"fileType":"text","operation":"modify","path":"<cwd>/src/app.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/src/app.ts <cwd>/src/app.ts\n--- <cwd>/src/app.ts\n+++ <cwd>/src/app.ts\n@@ -1 +1 @@\n-const value = 1;\n+const value = 2;\n"},"type":"diff"}],"kind":"edit","locations":[{"path":"<cwd>/src/app.ts"}],"name":"Edit","rawInput":{"file_path":"<cwd>/src/app.ts","new_string":"value = 2","old_string":"value = 1"},"title":"Edit src/app.ts","toolCallId":"toolu_edit"},"type":"tool_call"},"title":"Edit src/app.ts"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"```\nThe user doesn't want to proceed with this tool use. The tool use was rejected.\n```","type":"text"},"type":"content"}],"rawOutput":"The user doesn't want to proceed with this tool use. The tool use was rejected.","sessionUpdate":"tool_call_update","status":"failed","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/edit-with-permission.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/edit-with-permission.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"edit","locations":[],"name":"Edit","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Edit","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"path":"<cwd>/src/app.ts"}],"rawInput":{"file_path":"<cwd>/src/app.ts"},"sessionUpdate":"tool_call_update","title":"Edit src/app.ts","toolCallId":"toolu_edit"}}}
@@ -10,10 +10,10 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"file_path":"<cwd>/src/app.ts","new_string":"const value = 2;","old_string":"const value = 1;"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"changes":[{"fileType":"text","operation":"modify","path":"<cwd>/src/app.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/src/app.ts <cwd>/src/app.ts\n--- <cwd>/src/app.ts\n+++ <cwd>/src/app.ts\n@@ -1,3 +1,3 @@\n line 1\n-const value = 1;\n+const value = 2;\n line 3\n"},"type":"diff"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_edit"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"changes":[{"fileType":"text","operation":"modify","path":"<cwd>/src/app.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/src/app.ts <cwd>/src/app.ts\n--- <cwd>/src/app.ts\n+++ <cwd>/src/app.ts\n@@ -1,3 +1,3 @@\n line 1\n-const value = 1;\n+const value = 2;\n line 3\n"},"type":"diff"}],"kind":"edit","locations":[{"path":"<cwd>/src/app.ts"}],"name":"Edit","rawInput":{"file_path":"<cwd>/src/app.ts","new_string":"const value = 2;","old_string":"const value = 1;"},"title":"Edit src/app.ts","toolCallId":"toolu_edit"},"type":"tool_call"},"title":"Edit src/app.ts"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawOutput":"The file <cwd>/src/app.ts has been updated successfully.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"line":1,"path":"<cwd>/src/app.ts"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/exit-plan-approve.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/exit-plan-approve.jsonl
@@ -1,17 +1,17 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"switch_mode","name":"ExitPlanMode","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Approve Plan","toolCallId":"toolu_plan"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"# Plan\n1. Do it","type":"text"},"type":"content"}],"rawInput":{"plan":"# Plan\n1. Do it"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_plan"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes, manually approve edits","optionId":"exit-plan-default"},{"kind":"allow_always","name":"Yes, clear context (0% used) and use auto mode","optionId":"exit-plan-clear-auto"},{"kind":"allow_always","name":"Yes, and use auto mode","optionId":"exit-plan-auto"},{"kind":"allow_always","name":"Yes, and bypass permissions","optionId":"exit-plan-bypass"},{"kind":"reject_once","name":"No, keep planning","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"content":{"text":"# Plan\n1. Do it","type":"text"},"type":"content"}],"kind":"switch_mode","name":"ExitPlanMode","rawInput":{"plan":"# Plan\n1. Do it"},"title":"Approve Plan","toolCallId":"toolu_plan"},"type":"tool_call"},"title":"Ready to code?"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawOutput":"User has approved your plan. You can now start coding.\n\n## Approved Plan:\n# Plan\n1. Do it","sessionUpdate":"tool_call_update","status":"completed","title":"Exited Plan Mode","toolCallId":"toolu_plan"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"plan":{"content":"# Plan\n1. Do it","planId":"plan-mode","type":"markdown"},"sessionUpdate":"plan_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/exit-plan-reject.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/exit-plan-reject.jsonl
@@ -1,15 +1,15 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"switch_mode","name":"ExitPlanMode","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Approve Plan","toolCallId":"toolu_plan"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"# Plan\n1. Do it","type":"text"},"type":"content"}],"rawInput":{"plan":"# Plan\n1. Do it"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_plan"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes, manually approve edits","optionId":"exit-plan-default"},{"kind":"allow_always","name":"Yes, clear context (0% used) and use auto mode","optionId":"exit-plan-clear-auto"},{"kind":"allow_always","name":"Yes, and use auto mode","optionId":"exit-plan-auto"},{"kind":"allow_always","name":"Yes, and bypass permissions","optionId":"exit-plan-bypass"},{"kind":"reject_once","name":"No, keep planning","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"content":{"text":"# Plan\n1. Do it","type":"text"},"type":"content"}],"kind":"switch_mode","name":"ExitPlanMode","rawInput":{"plan":"# Plan\n1. Do it"},"title":"Approve Plan","toolCallId":"toolu_plan"},"type":"tool_call"},"title":"Ready to code?"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"```\n```\nThe user doesn't want to proceed with this tool use.\n```\n```","type":"text"},"type":"content"}],"rawOutput":"The user doesn't want to proceed with this tool use.","sessionUpdate":"tool_call_update","status":"failed","toolCallId":"toolu_plan"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/goal.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/goal.jsonl
@@ -1,6 +1,6 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"/goal Ship the feature","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/grep-and-glob.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/grep-and-glob.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"search","name":"Grep","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"grep","toolCallId":"toolu_grep"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"pattern":"value"},"sessionUpdate":"tool_call_update","title":"grep \"value\"","toolCallId":"toolu_grep"}}}
@@ -16,4 +16,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"pattern":"**/*.ts"},"sessionUpdate":"tool_call_update","title":"Find `**/*.ts`","toolCallId":"toolu_glob"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"src/app.ts\nsrc/b.ts","type":"text"},"type":"content"}],"rawOutput":"src/app.ts\nsrc/b.ts","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_glob"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/mcp-tool.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/mcp-tool.jsonl
@@ -1,15 +1,15 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"other","name":"mcp__docs__search","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"mcp__docs__search","toolCallId":"toolu_mcp"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"q":"acp"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_mcp"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"_meta":{"claudeCode":{"mcpServer":{"name":"docs","source":"project"}}},"content":[],"kind":"other","name":"mcp__docs__search","rawInput":{"q":"acp"},"title":"mcp__docs__search","toolCallId":"toolu_mcp"},"type":"tool_call"},"title":"mcp__docs__search"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"Found 2 documents.","type":"text"},"type":"content"}],"rawOutput":[{"text":"Found 2 documents.","type":"text"}],"sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_mcp"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/memory-recall.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/memory-recall.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"claudeCode":{"toolResponse":{"mode":"select"}}},"kind":"read","locations":[{"path":"/memory/a.md"},{"path":"/memory/b.md"}],"name":"memory_recall","sessionUpdate":"tool_call_update","status":"completed","title":"Recalled 2 memories","toolCallId":"00000000-0000-4000-8000-000000000001"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"claudeCode":{"toolResponse":{"mode":"synthesize"}}},"content":[{"content":{"text":"The user prefers tabs.","type":"text"},"type":"content"}],"kind":"read","name":"memory_recall","sessionUpdate":"tool_call_update","status":"completed","title":"Recalled synthesized memory","toolCallId":"00000000-0000-4000-8000-000000000002"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/network-permission.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/network-permission.jsonl
@@ -1,11 +1,11 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"other","name":"SandboxNetworkAccess","rawInput":{"host":"example.com"},"sessionUpdate":"tool_call_update","status":"pending","title":"SandboxNetworkAccess","toolCallId":"toolu_net"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"description":"Reason: Sandbox blocks network","options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"content":{"text":"```json\n{\n  \"host\": \"example.com\"\n}\n```","type":"text"},"type":"content"}],"kind":"other","name":"SandboxNetworkAccess","rawInput":{"host":"example.com"},"title":"example.com","toolCallId":"toolu_net"},"type":"tool_call"},"title":"example.com"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_net"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/notebook-edit.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/notebook-edit.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"other","name":"NotebookEdit","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"NotebookEdit","toolCallId":"toolu_nb"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"notebook_path":"<cwd>/n.ipynb"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_nb"}}}
@@ -10,9 +10,9 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"cell_id":"cell-1","new_source":"print('hi')","notebook_path":"<cwd>/n.ipynb"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_nb"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"cell_id":"cell-1","edit_mode":"replace","new_source":"print('hi')","notebook_path":"<cwd>/n.ipynb"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_nb"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[],"kind":"other","name":"NotebookEdit","rawInput":{"cell_id":"cell-1","edit_mode":"replace","new_source":"print('hi')","notebook_path":"<cwd>/n.ipynb"},"title":"NotebookEdit","toolCallId":"toolu_nb"},"type":"tool_call"},"title":"NotebookEdit"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"Updated cell cell-1 with print('hi')","type":"text"},"type":"content"}],"rawOutput":"Updated cell cell-1 with print('hi')","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_nb"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/permission-denied.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/permission-denied.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"terminal_update","terminalId":"toolu_denied"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"terminalId":"toolu_denied","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Terminal","toolCallId":"toolu_denied"}}}
@@ -14,4 +14,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"exitStatus":{},"sessionUpdate":"terminal_update","terminalId":"toolu_denied"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"terminalId":"toolu_denied","type":"terminal"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_denied"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/rate-limit-and-origin.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/rate-limit-and-origin.jsonl
@@ -1,12 +1,12 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"Work","type":"text"},"messageId":"msg_rate","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"ing.","type":"text"},"messageId":"msg_rate","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6","_claude/rateLimit":{"resetsAt":1700000000,"status":"allowed_warning","utilization":0.9}},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6","_claude/origin":{"kind":"human"}},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/read.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/read.jsonl
@@ -1,12 +1,12 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"read","locations":[],"name":"Read","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Read File","toolCallId":"toolu_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"line":1,"path":"<cwd>/a.ts"}],"rawInput":{"file_path":"<cwd>/a.ts"},"sessionUpdate":"tool_call_update","title":"Read a.ts","toolCallId":"toolu_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"```\n1\tconst a = 1;\n```","type":"text"},"type":"content"}],"rawOutput":"1\tconst a = 1;\n<system-reminder>x</system-reminder>","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/session-load-replay.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/session-load-replay.jsonl
@@ -18,5 +18,5 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"Fixed.","type":"text"},"messageId":"msg_r2","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"description":"The history of 1 subagent of this session could not be restored.","sessionUpdate":"notice","severity":"info","title":"Some subagent history is not available"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"session_info_update","title":"Fix the app","updatedAt":"2026-01-01T00:00:00.000Z"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"idle"}}}
-{"kind":"response","method":"session/resume","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}]}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"idle"}}}
+{"kind":"response","method":"session/resume","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}]}}
--- a/src/tests/acp-scenarios/snapshots/v2/session-setup.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/session-setup.jsonl
@@ -1,2 +1,2 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
--- a/src/tests/acp-scenarios/snapshots/v2/skill.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/skill.jsonl
@@ -1,12 +1,12 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"other","name":"Skill","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Load skill","toolCallId":"toolu_skill"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"skill":"commits"},"sessionUpdate":"tool_call_update","title":"Load skill: commits","toolCallId":"toolu_skill"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawOutput":"Launching skill: commits","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_skill"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/subagent-agent-async.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/subagent-agent-async.jsonl
@@ -1,18 +1,18 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"general-purpose","sessionId":"a2","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Background review"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"general-purpose","sessionId":"a2","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Background review"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Review the diff","type":"text"}],"messageId":"toolu_agent","recipientMessageId":"toolu_agent","recipientSessionId":"a2","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"content":[{"text":"Review the diff","type":"text"}],"messageId":"toolu_agent","recipientSessionId":"a2","senderMessageId":"toolu_agent","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_agent"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_agent"}},"content":{"text":"Reviewi","type":"text"},"messageId":"msg_async_sub","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_agent"}},"content":{"text":"ng now.","type":"text"},"messageId":"msg_async_sub","sessionUpdate":"agent_message_chunk"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"a2","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"end_turn"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"a2","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"end_turn"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"a2","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/subagent-late-child-update.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/subagent-late-child-update.jsonl
@@ -1,21 +1,21 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"general-purpose","sessionId":"agent_late","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Check the logs"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"general-purpose","sessionId":"agent_late","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Check the logs"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Check logs","type":"text"}],"messageId":"toolu_late","recipientMessageId":"toolu_late","recipientSessionId":"agent_late","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"content":[{"text":"Check logs","type":"text"}],"messageId":"toolu_late","recipientSessionId":"agent_late","senderMessageId":"toolu_late","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_late"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_late"}},"content":[],"kind":"read","locations":[],"name":"Read","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Read File","toolCallId":"toolu_late_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"locations":[{"line":1,"path":"/var/log/app.log"}],"rawInput":{"file_path":"/var/log/app.log"},"sessionUpdate":"tool_call_update","title":"Read /var/log/app.log","toolCallId":"toolu_late_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"The logs are clean.","type":"text"}],"messageId":"toolu_late:reply","recipientSessionId":"<session>","senderSessionId":"agent_late","sessionUpdate":"session_message"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_late","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"end_turn"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_late","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"end_turn"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_late","toolResponse":{"elapsedTimeSeconds":4}}},"sessionUpdate":"tool_call_update","status":"in_progress","toolCallId":"toolu_late_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_late","update":{"content":[{"content":{"text":"```\n1\tok\n```","type":"text"},"type":"content"}],"rawOutput":"1\tok","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_late_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/subagent-native-sessions.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/subagent-native-sessions.jsonl
@@ -1,12 +1,12 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"general-purpose","sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Fix the build"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"general-purpose","sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Fix the build"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Make the build pass","type":"text"}],"messageId":"toolu_native","recipientMessageId":"toolu_native","recipientSessionId":"agent_n","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"content":[{"text":"Make the build pass","type":"text"}],"messageId":"toolu_native","recipientSessionId":"agent_n","senderMessageId":"toolu_native","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_native"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
@@ -21,17 +21,17 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"command":"make","sessionUpdate":"terminal_update","terminalId":"toolu_native_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"rawInput":{"command":"make"},"sessionUpdate":"tool_call_update","title":"make","toolCallId":"toolu_native_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"rawInput":{"command":"make","description":"Build"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_native_bash"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"state":"requires_action"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"background":[],"state":"requires_action"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"agent_n","subject":{"toolCall":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_native"}},"content":[{"terminalId":"toolu_native_bash","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{"command":"make","description":"Build"},"title":"make","toolCallId":"toolu_native_bash"},"type":"tool_call"},"title":"make"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"state":"running"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"output":{"data":"bWFrZTogKioqIEVycm9yIDI="},"sessionUpdate":"terminal_update","terminalId":"toolu_native_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"exitStatus":{},"sessionUpdate":"terminal_update","terminalId":"toolu_native_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"sessionUpdate":"tool_call_update","status":"failed","toolCallId":"toolu_native_bash"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"error"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"error"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_n","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"error"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_n","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"error"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/subagent-nested.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/subagent-nested.jsonl
@@ -1,17 +1,17 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"Plan","sessionId":"agent_outer","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Plan the work"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"Plan","sessionId":"agent_outer","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Plan the work"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Plan it","type":"text"}],"messageId":"toolu_outer","recipientMessageId":"toolu_outer","recipientSessionId":"agent_outer","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"content":[{"text":"Plan it","type":"text"}],"messageId":"toolu_outer","recipientSessionId":"agent_outer","senderMessageId":"toolu_outer","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_outer"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"capabilities":{"cancel":{}},"description":"Explore","sessionId":"agent_inner","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Read the spec"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"capabilities":{"cancel":{}},"description":"Explore","sessionId":"agent_inner","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Read the spec"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"content":[{"text":"Read spec.md","type":"text"}],"messageId":"toolu_inner","recipientMessageId":"toolu_inner","recipientSessionId":"agent_inner","senderSessionId":"agent_outer","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"content":[{"text":"Read spec.md","type":"text"}],"messageId":"toolu_inner","recipientSessionId":"agent_inner","senderMessageId":"toolu_inner","senderSessionId":"agent_outer","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_inner"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
@@ -19,12 +19,12 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"locations":[{"line":1,"path":"/spec.md"}],"rawInput":{"file_path":"/spec.md"},"sessionUpdate":"tool_call_update","title":"Read /spec.md","toolCallId":"toolu_grandchild_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"content":[{"content":{"text":"```\n1\tspec\n```","type":"text"},"type":"content"}],"rawOutput":"1\tspec","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_grandchild_read"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"content":[{"text":"The spec says X.","type":"text"}],"messageId":"toolu_inner:reply","recipientSessionId":"agent_outer","senderSessionId":"agent_inner","sessionUpdate":"session_message"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"sessionId":"agent_inner","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"end_turn"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"sessionId":"agent_inner","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"end_turn"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_inner","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_outer"}},"content":{"text":"Plan:","type":"text"},"messageId":"msg_outer_text","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_outer"}},"content":{"text":" do X.","type":"text"},"messageId":"msg_outer_text","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Plan: do X.","type":"text"}],"messageId":"toolu_outer:reply","recipientSessionId":"<session>","senderSessionId":"agent_outer","sessionUpdate":"session_message"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_outer","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"end_turn"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_outer","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"end_turn"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_outer","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/subagent-task-legacy.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/subagent-task-legacy.jsonl
@@ -1,12 +1,12 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"Explore","sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Explore code"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"Explore","sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Explore code"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Find the parser","type":"text"}],"messageId":"toolu_task","recipientMessageId":"toolu_task","recipientSessionId":"agent_1","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"content":[{"text":"Find the parser","type":"text"}],"messageId":"toolu_task","recipientSessionId":"agent_1","senderMessageId":"toolu_task","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_task"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
@@ -20,13 +20,13 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"command":"rg parser","sessionUpdate":"terminal_update","terminalId":"toolu_sub_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"rawInput":{"command":"rg parser"},"sessionUpdate":"tool_call_update","title":"rg parser","toolCallId":"toolu_sub_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"rawInput":{"command":"rg parser","description":"Search"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_sub_bash"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"state":"requires_action"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"background":[],"state":"requires_action"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"agent_1","subject":{"toolCall":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_task"}},"content":[{"terminalId":"toolu_sub_bash","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{"command":"rg parser","description":"Search"},"title":"rg parser","toolCallId":"toolu_sub_bash"},"type":"tool_call"},"title":"rg parser"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"state":"running"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"output":{"data":"eC50cw=="},"sessionUpdate":"terminal_update","terminalId":"toolu_sub_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"exitStatus":{"exitCode":0},"sessionUpdate":"terminal_update","terminalId":"toolu_sub_bash"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_sub_bash"}}}
@@ -34,19 +34,19 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"locations":[{"path":"<cwd>/x.ts"}],"rawInput":{"file_path":"<cwd>/x.ts"},"sessionUpdate":"tool_call_update","title":"Edit x.ts","toolCallId":"toolu_sub_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"rawInput":{"file_path":"<cwd>/x.ts","old_string":"a"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_sub_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"rawInput":{"file_path":"<cwd>/x.ts","new_string":"b","old_string":"a"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_sub_edit"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"state":"requires_action"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"background":[],"state":"requires_action"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"agent_1","subject":{"toolCall":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_task"}},"content":[],"kind":"edit","locations":[{"path":"<cwd>/x.ts"}],"name":"Edit","rawInput":{"file_path":"<cwd>/x.ts","new_string":"b","old_string":"a"},"title":"Edit x.ts","toolCallId":"toolu_sub_edit"},"type":"tool_call"},"title":"Edit x.ts"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"state":"running"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"rawOutput":"The file has been updated.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_sub_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"content":[{"changes":[{"fileType":"text","operation":"modify","path":"<cwd>/x.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/x.ts <cwd>/x.ts\n--- <cwd>/x.ts\n+++ <cwd>/x.ts\n@@ -1 +1 @@\n-a\n+b\n"},"type":"diff"}],"locations":[{"line":1,"path":"<cwd>/x.ts"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_sub_edit"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_task"}},"content":{"text":"Foun","type":"text"},"messageId":"msg_sub_2","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_task"}},"content":{"text":"d it.","type":"text"},"messageId":"msg_sub_2","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"The parser is in x.ts.","type":"text"}],"messageId":"toolu_task:reply","recipientSessionId":"<session>","senderSessionId":"agent_1","sessionUpdate":"session_message"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"end_turn"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_1","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"end_turn"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_1","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/subagent-transcript-extension.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/subagent-transcript-extension.jsonl
@@ -1,12 +1,12 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"Explore","sessionId":"agent_t","sessionUpdate":"subagent_update","state":{"state":"running"},"title":"Summarize"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"capabilities":{"cancel":{}},"description":"Explore","sessionId":"agent_t","sessionUpdate":"subagent_update","state":{"background":[],"state":"running"},"title":"Summarize"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Summarize the repo","type":"text"}],"messageId":"toolu_transcript","recipientMessageId":"toolu_transcript","recipientSessionId":"agent_t","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"content":[{"text":"Summarize the repo","type":"text"}],"messageId":"toolu_transcript","recipientSessionId":"agent_t","senderMessageId":"toolu_transcript","senderSessionId":"<session>","sessionUpdate":"session_message"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"_meta":{"claudeCode":{"parentToolUseId":"toolu_transcript"}},"configOptions":[{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","name":"Model","options":[{"name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionUpdate":"config_option_update"}}}
@@ -18,7 +18,7 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"rawInput":{"pattern":"*"},"sessionUpdate":"tool_call_update","title":"Find `*`","toolCallId":"toolu_transcript_glob"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"content":[{"content":{"text":"a\nb","type":"text"},"type":"content"}],"rawOutput":"a\nb","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_transcript_glob"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"Two packages.","type":"text"}],"messageId":"toolu_transcript:reply","recipientSessionId":"<session>","senderSessionId":"agent_t","sessionUpdate":"session_message"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_t","sessionUpdate":"subagent_update","state":{"state":"idle","stopReason":"end_turn"}}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionId":"agent_t","sessionUpdate":"subagent_update","state":{"background":[],"state":"idle","stopReason":"end_turn"}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"agent_t","update":{"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/task-create-update.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/task-create-update.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"plan":{"entries":[{"content":"Write tests","priority":"medium","status":"pending"}],"planId":"plan","type":"items"},"sessionUpdate":"plan_update"}}}
@@ -13,13 +13,13 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"plan":{"entries":[{"content":"Write tests","priority":"medium","status":"completed"}],"planId":"plan","type":"items"},"sessionUpdate":"plan_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"plan":{"entries":[{"content":"Write tests","priority":"medium","status":"completed"}],"planId":"plan","type":"items"},"sessionUpdate":"plan_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 2","type":"text"}],"messageId":"<id-2>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-2>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"All ","type":"text"},"messageId":"msg_follow","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"done.","type":"text"},"messageId":"msg_follow","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/task-output-and-stop.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/task-output-and-stop.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"other","name":"TaskOutput","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"TaskOutput","toolCallId":"toolu_out"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"task_id":"bash_1"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_out"}}}
@@ -14,4 +14,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"task_id":"bash_1"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_stop"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"Successfully stopped task: bash_1","type":"text"},"type":"content"}],"rawOutput":"Successfully stopped task: bash_1","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_stop"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/text-and-thinking.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/text-and-thinking.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"Let me thin","type":"text"},"messageId":"msg_text","sessionUpdate":"agent_thought_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"k about it.","type":"text"},"messageId":"msg_text","sessionUpdate":"agent_thought_chunk"}}}
@@ -10,4 +10,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":{"text":"he answer.","type":"text"},"messageId":"msg_text","sessionUpdate":"agent_message_chunk"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/todo-write.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/todo-write.jsonl
@@ -1,10 +1,10 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"plan":{"entries":[{"content":"Writing tests","priority":"medium","status":"in_progress"},{"content":"Ship","priority":"medium","status":"pending"}],"planId":"plan","type":"items"},"sessionUpdate":"plan_update"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/tool-progress.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/tool-progress.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"terminal_update","terminalId":"toolu_slow"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"terminalId":"toolu_slow","type":"terminal"}],"kind":"execute","name":"Bash","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Terminal","toolCallId":"toolu_slow"}}}
@@ -16,4 +16,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"exitStatus":{"exitCode":0},"sessionUpdate":"terminal_update","terminalId":"toolu_slow"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_slow"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/web-fetch-and-search.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/web-fetch-and-search.jsonl
@@ -1,20 +1,20 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"fetch","name":"WebFetch","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Fetch","toolCallId":"toolu_fetch"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"url":"https://example.com"},"sessionUpdate":"tool_call_update","title":"Fetch https://example.com","toolCallId":"toolu_fetch"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"Summarize the page","type":"text"},"type":"content"}],"rawInput":{"prompt":"Summarize the page","url":"https://example.com"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_fetch"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"allow_always","name":"Yes, and don't ask again for example.com","optionId":"allow-with-updates"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"content":{"text":"Summarize the page","type":"text"},"type":"content"}],"kind":"fetch","name":"WebFetch","rawInput":{"prompt":"Summarize the page","url":"https://example.com"},"title":"Fetch https://example.com","toolCallId":"toolu_fetch"},"type":"tool_call"},"title":"Fetch https://example.com"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"The page is an example.","type":"text"},"type":"content"}],"rawOutput":"The page is an example.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_fetch"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"fetch","name":"WebSearch","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Web search","toolCallId":"toolu_search"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"query":"acp protocol"},"sessionUpdate":"tool_call_update","title":"Search \"acp protocol\"","toolCallId":"toolu_search"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"content":{"text":"ACP (https://agentclientprotocol.com)\nA summary.","type":"text"},"type":"content"}],"rawOutput":"Web search results for query: \"acp protocol\"\n\nLinks: [...]","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_search"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/write-existing.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/write-existing.jsonl
@@ -1,8 +1,8 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"edit","locations":[],"name":"Write","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Preparing file…","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"path":"<cwd>/old.ts"}],"rawInput":{"file_path":"<cwd>/old.ts"},"sessionUpdate":"tool_call_update","title":"Write old.ts","toolCallId":"toolu_write"}}}
@@ -12,4 +12,4 @@
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawOutput":"The file <cwd>/old.ts has been updated successfully.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"line":1,"path":"<cwd>/old.ts"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/snapshots/v2/write-new.jsonl
+++ b/src/tests/acp-scenarios/snapshots/v2/write-new.jsonl
@@ -1,17 +1,17 @@
 {"kind":"response","method":"initialize","payload":{"authMethods":[],"capabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"providers":{},"session":{"additionalDirectories":{},"delete":{},"fork":{},"mcp":{"http":{},"stdio":{}},"prompt":{"embeddedContext":{},"image":{}},"systemPrompt":{"mode":{"override":{}}}}},"info":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"protocolVersion":2}}
-{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"default","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
+{"kind":"response","method":"session/new","payload":{"availableCommands":[{"description":"Show the MCP servers and their status, or reconnect, enable, or disable a server","input":{"hint":"[reconnect|enable|disable [<server>|all]]","type":"text"},"name":"mcp","type":"command"}],"configOptions":[{"category":"mode","configId":"mode","currentValue":"auto","description":"Session permission mode","name":"Mode","options":[{"description":"Always ask before making changes","name":"Manual","value":"default"},{"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","configId":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"sessionId":"<session>"}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"text":"prompt 1","type":"text"}],"messageId":"<id-1>","sessionUpdate":"user_message"}}}
 {"kind":"response","method":"session/prompt","payload":{"messageId":"<id-1>"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[],"kind":"edit","locations":[],"name":"Write","rawInput":{},"sessionUpdate":"tool_call_update","status":"pending","title":"Preparing file…","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"locations":[{"path":"<cwd>/new.ts"}],"rawInput":{"file_path":"<cwd>/new.ts"},"sessionUpdate":"tool_call_update","title":"Write new.ts","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"sessionUpdate":"usage_update","size":200000,"used":3}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawInput":{"content":"export const x = 1;\n","file_path":"<cwd>/new.ts"},"sessionUpdate":"tool_call_update","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"content":[{"changes":[{"fileType":"text","operation":"add","path":"<cwd>/new.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/new.ts <cwd>/new.ts\nnew file mode 100644\n--- /dev/null\n+++ <cwd>/new.ts\n@@ -0,0 +1 @@\n+export const x = 1;\n"},"type":"diff"}],"sessionUpdate":"tool_call_update","toolCallId":"toolu_write"}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"requires_action"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"requires_action"}}}
 {"kind":"request","method":"session/request_permission","payload":{"options":[{"kind":"allow_once","name":"Yes","optionId":"allow-once"},{"kind":"reject_once","name":"No","optionId":"reject"}],"sessionId":"<session>","subject":{"toolCall":{"content":[{"changes":[{"fileType":"text","operation":"add","path":"<cwd>/new.ts"}],"patch":{"format":"git_patch","text":"diff --git <cwd>/new.ts <cwd>/new.ts\nnew file mode 100644\n--- /dev/null\n+++ <cwd>/new.ts\n@@ -0,0 +1 @@\n+export const x = 1;\n"},"type":"diff"}],"kind":"edit","locations":[{"path":"<cwd>/new.ts"}],"name":"Write","rawInput":{"content":"export const x = 1;\n","file_path":"<cwd>/new.ts"},"title":"Write new.ts","toolCallId":"toolu_write"},"type":"tool_call"},"title":"Write new.ts"}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"sessionUpdate":"state_update","state":"running"}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"background":[],"sessionUpdate":"state_update","state":"running"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"rawOutput":"File created successfully at: <cwd>/new.ts","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_write"}}}
 {"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"_claude/model":"claude-sonnet-4-6"},"cost":{"amount":0,"currency":"USD"},"sessionUpdate":"usage_update","size":200000,"used":2}}}
-{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
+{"kind":"notification","method":"session/update","payload":{"sessionId":"<session>","update":{"_meta":{"quota":{"model_usage":[],"token_count":{"cachedInputTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"reasoningOutputTokens":0,"totalTokens":0}}},"background":[],"sessionUpdate":"state_update","state":"idle","stopReason":"end_turn","usage":{"cachedReadTokens":0,"cachedWriteTokens":0,"inputTokens":0,"outputTokens":0,"totalTokens":0}}}}
--- a/src/tests/acp-scenarios/harness.ts
+++ b/src/tests/acp-scenarios/harness.ts
@@ -500,21 +500,17 @@ export async function runScenarioV2(
  const idles: unknown[] = [];
  const failures: string[] = [];

-  const each = (message: v2.AnyWireMessage) =>
-    (Array.isArray(message) ? message : [message]) as Record<string, any>[];
-  const toAgent = new TransformStream<v2.AnyWireMessage, v2.AnyWireMessage>({
+  const toAgent = new TransformStream<v2.AnyMessage, v2.AnyMessage>({
    transform(message, controller) {
-      for (const m of each(message)) {
-        if ("method" in m && "id" in m) methodsOfClientRequests.set(m.id, m.method);
+      if ("method" in message && "id" in message && message.id !== null) {
+        methodsOfClientRequests.set(message.id, message.method);
      }
      controller.enqueue(message);
    },
  });
-  const toClient = new TransformStream<v2.AnyWireMessage, v2.AnyWireMessage>({
+  const toClient = new TransformStream<v2.AnyMessage, v2.AnyMessage>({
    transform(message, controller) {
-      for (const m of each(message)) {
-        if (recording) raw.push(wireRecord(m, methodsOfClientRequests));
-      }
+      if (recording) raw.push(wireRecord(message, methodsOfClientRequests));
      controller.enqueue(message);
    },
  });
--- a/src/tests/acp-scenarios/origin-main/plain/session-load-replay.jsonl
+++ b/src/tests/acp-scenarios/origin-main/plain/session-load-replay.jsonl
@@ -9,5 +9,5 @@
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"_meta":{"claudeCode":{"toolName":"Edit"}},"rawOutput":"The file <cwd>/src/app.ts has been updated successfully.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_r_edit"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"_meta":{"claudeCode":{"toolName":"Task"}},"content":[{"content":{"text":"Report.","type":"text"},"type":"content"}],"rawOutput":"Report.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_r_task"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"content":{"text":"Fixed.","type":"text"},"messageId":"msg_r2","sessionUpdate":"agent_message_chunk"}}}
-{"kind":"loadSession","payload":{"configOptions":[{"category":"mode","currentValue":"default","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"default"},"sessionId":"<session>"}}
+{"kind":"loadSession","payload":{"configOptions":[{"category":"mode","currentValue":"auto","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"auto"},"sessionId":"<session>"}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"availableCommands":[],"sessionUpdate":"available_commands_update"}}}
--- a/src/tests/acp-scenarios/origin-main/plain/session-setup.jsonl
+++ b/src/tests/acp-scenarios/origin-main/plain/session-setup.jsonl
@@ -1,3 +1,3 @@
 {"kind":"initialize","payload":{"_meta":{"goal":{"actions":["set","clear"],"controlMethod":"_session/goal","version":1},"jetbrains":{"air":{"capabilities":["sessionFailure","agentFileChangeReport","nativeSubagentSessions","asyncTasks","recommendedValue"],"version":1}},"steering":{"supported":true}},"agentCapabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"auth":{"logout":{}},"loadSession":true,"mcpCapabilities":{"http":true,"sse":true},"promptCapabilities":{"embeddedContext":true,"image":true},"providers":{},"sessionCapabilities":{"additionalDirectories":{},"close":{},"delete":{},"fork":{},"list":{},"resume":{},"subagents":{}}},"agentInfo":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"authMethods":[],"protocolVersion":1}}
-{"kind":"newSession","payload":{"configOptions":[{"category":"mode","currentValue":"default","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"default"},"sessionId":"<session>"}}
+{"kind":"newSession","payload":{"configOptions":[{"category":"mode","currentValue":"auto","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"auto"},"sessionId":"<session>"}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"availableCommands":[],"sessionUpdate":"available_commands_update"}}}
--- a/src/tests/acp-scenarios/origin-main/zed/session-load-replay.jsonl
+++ b/src/tests/acp-scenarios/origin-main/zed/session-load-replay.jsonl
@@ -10,5 +10,5 @@
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"_meta":{"claudeCode":{"toolName":"Edit"}},"rawOutput":"The file <cwd>/src/app.ts has been updated successfully.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_r_edit"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"_meta":{"claudeCode":{"toolName":"Task"}},"content":[{"content":{"text":"Report.","type":"text"},"type":"content"}],"rawOutput":"Report.","sessionUpdate":"tool_call_update","status":"completed","toolCallId":"toolu_r_task"}}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"content":{"text":"Fixed.","type":"text"},"messageId":"msg_r2","sessionUpdate":"agent_message_chunk"}}}
-{"kind":"loadSession","payload":{"configOptions":[{"category":"mode","currentValue":"default","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"default"},"sessionId":"<session>"}}
+{"kind":"loadSession","payload":{"configOptions":[{"category":"mode","currentValue":"auto","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"auto"},"sessionId":"<session>"}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"availableCommands":[],"sessionUpdate":"available_commands_update"}}}
--- a/src/tests/acp-scenarios/origin-main/zed/session-setup.jsonl
+++ b/src/tests/acp-scenarios/origin-main/zed/session-setup.jsonl
@@ -1,3 +1,3 @@
 {"kind":"initialize","payload":{"_meta":{"goal":{"actions":["set","clear"],"controlMethod":"_session/goal","version":1},"jetbrains":{"air":{"capabilities":["sessionFailure","agentFileChangeReport","nativeSubagentSessions","asyncTasks","recommendedValue"],"version":1}},"steering":{"supported":true}},"agentCapabilities":{"_meta":{"authStatus":{},"claudeCode":{"promptQueueing":true}},"auth":{"logout":{}},"loadSession":true,"mcpCapabilities":{"http":true,"sse":true},"promptCapabilities":{"embeddedContext":true,"image":true},"providers":{},"sessionCapabilities":{"additionalDirectories":{},"close":{},"delete":{},"fork":{},"list":{},"resume":{},"subagents":{}}},"agentInfo":{"name":"@agentclientprotocol/claude-agent-acp","title":"Claude Agent","version":"<version>"},"authMethods":[{"_meta":{"terminal-auth":{"args":["<argv>","--cli","auth","login","--claudeai"],"command":"<executable>","label":"Claude Login"}},"args":["--cli","auth","login","--claudeai"],"description":"Use Claude subscription ","id":"claude-ai-login","name":"Claude Subscription","type":"terminal"},{"_meta":{"terminal-auth":{"args":["<argv>","--cli","auth","login","--console"],"command":"<executable>","label":"Anthropic Console Login"}},"args":["--cli","auth","login","--console"],"description":"Use Anthropic Console (API usage billing)","id":"console-login","name":"Anthropic Console","type":"terminal"}],"protocolVersion":1}}
-{"kind":"newSession","payload":{"configOptions":[{"category":"mode","currentValue":"default","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"default"},"sessionId":"<session>"}}
+{"kind":"newSession","payload":{"configOptions":[{"category":"mode","currentValue":"auto","description":"Session permission mode","id":"mode","name":"Mode","options":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","name":"Manual","value":"default"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","name":"Accept edits","value":"acceptEdits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","name":"Plan","value":"plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","name":"Auto","value":"auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","name":"Bypass permissions","value":"bypassPermissions"}],"type":"select"},{"category":"model","currentValue":"claude-sonnet-4-6","description":"AI model to use","id":"model","name":"Model","options":[{"description":"Fast","name":"Claude Sonnet 4.6","value":"claude-sonnet-4-6"}],"type":"select"}],"modes":{"availableModes":[{"_meta":{"kind":"standard"},"description":"Always ask before making changes","id":"default","name":"Manual"},{"_meta":{"kind":"standard"},"description":"Automatically accept all file edits","id":"acceptEdits","name":"Accept edits"},{"_meta":{"kind":"plan"},"description":"Create a plan before making changes","id":"plan","name":"Plan"},{"_meta":{"kind":"auto_review"},"description":"Claude handles permission decisions","id":"auto","name":"Auto"},{"_meta":{"kind":"full_access"},"description":"Accepts all permissions","id":"bypassPermissions","name":"Bypass permissions"}],"currentModeId":"auto"},"sessionId":"<session>"}}
 {"kind":"sessionUpdate","payload":{"sessionId":"<session>","update":{"availableCommands":[],"sessionUpdate":"available_commands_update"}}}
--- a/src/tests/acp-v2.test.ts
+++ b/src/tests/acp-v2.test.ts
--- a/src/tests/agent-command.test.ts
+++ b/src/tests/agent-command.test.ts
@@ -0,0 +1,24 @@
+import { describe, expect, it } from "vitest";
+import { agentCommand } from "../agent-command.js";
+
+describe("agentCommand", () => {
+  it.each([
+    {
+      runtime: "Node",
+      argv: ["/usr/bin/node", "/opt/acp/dist/index.js", "--hide-claude-auth"],
+      args: ["/opt/acp/dist/index.js", "--hide-claude-auth"],
+    },
+    {
+      runtime: "a compiled executable",
+      argv: ["bun", "/$bunfs/root/claude-agent-acp", "--hide-claude-auth"],
+      args: ["--hide-claude-auth"],
+    },
+    {
+      runtime: "a compiled Windows executable",
+      argv: ["bun", "B:\\~BUN\\root\\claude-agent-acp.exe", "--hide-claude-auth"],
+      args: ["--hide-claude-auth"],
+    },
+  ])("reruns $runtime with its own flags", ({ argv, args }) => {
+    expect(agentCommand(argv)).toEqual({ command: process.execPath, args });
+  });
+});
--- a/src/tests/authorization.test.ts
+++ b/src/tests/authorization.test.ts
@@ -1076,6 +1076,62 @@ describe("authorization", () => {
        expect([...respawned.sessionFailureState.active.values()]).toHaveLength(0);
      });

+      it("restores the user's choices on the respawned query, then a choice sent meanwhile", async () => {
+        const [agent, updates] = createRecordingAgent(true);
+        hideClaudeAuth();
+        const effortModels = ["sonnet", "opus"].map((value) => ({
+          value,
+          displayName: value,
+          description: "",
+          supportsAutoMode: true,
+          supportsEffort: true,
+          supportedEffortLevels: ["low", "medium", "high"],
+        }));
+        const scripts = [[[signOutResult()]], [[successResult()]]];
+        let releaseRespawn!: () => void;
+        const respawnGate = new Promise<void>((resolve) => (releaseRespawn = resolve));
+        const queries: any[] = [];
+        mockQuery.mockImplementation((args: any) => {
+          const query = scriptedQuery(args, SIGNED_IN_WITH_KEY, scripts[queries.length] ?? []);
+          const gate = queries.length > 0 ? respawnGate : undefined;
+          query.initializationResult = async () => {
+            await gate;
+            return { models: effortModels, account: SIGNED_IN_WITH_KEY };
+          };
+          query.setModel = vi.fn(async () => {});
+          query.applyFlagSettings = vi.fn(async () => {});
+          queries.push(query);
+          return query;
+        });
+        const { sessionId } = await agent.newSession(newSessionParams());
+        await agent.setSessionConfigOption({ sessionId, configId: "model", value: "opus" });
+        await agent.setSessionConfigOption({ sessionId, configId: "effort", value: "high" });
+        await expect(agent.prompt(promptParams(sessionId))).rejects.toMatchObject({
+          code: AUTH_REQUIRED_CODE,
+        });
+
+        const turn = agent.prompt(promptParams(sessionId));
+        await vi.waitFor(() => expect(queries).toHaveLength(2));
+        const choice = agent.setSessionConfigOption({
+          sessionId,
+          configId: "effort",
+          value: "low",
+        });
+        releaseRespawn();
+        await expect(turn).resolves.toMatchObject({ stopReason: "end_turn" });
+        await choice;
+
+        expect(queries[1].setModel).toHaveBeenCalledWith("opus");
+        expect(queries[1].applyFlagSettings.mock.calls).toEqual([
+          [{ effortLevel: "high" }],
+          [{ effortLevel: "low" }],
+        ]);
+        expect(updates).toContainEqual({
+          sessionId,
+          update: expect.objectContaining({ sessionUpdate: "config_option_update" }),
+        });
+      });
+
      it("refuses with the plain error and no second row when still signed out", async () => {
        const [agent, updates] = createRecordingAgent(true);
        hideClaudeAuth();
--- a/src/tests/background-output.test.ts
+++ b/src/tests/background-output.test.ts
@@ -0,0 +1,129 @@
+import { appendFile, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  BACKGROUND_OUTPUT_MAX_BACKLOG_BYTES,
+  BACKGROUND_OUTPUT_READ_BYTES,
+  type BackgroundOutput,
+  BackgroundOutputTail,
+} from "../background-output.js";
+
+describe("BackgroundOutputTail", () => {
+  let dir: string;
+  let file: string;
+  let published: BackgroundOutput[];
+  let tail: BackgroundOutputTail | undefined;
+  const follow = () =>
+    (tail = new BackgroundOutputTail(file, async (output) => void published.push(output)));
+
+  beforeEach(async () => {
+    dir = await mkdtemp(path.join(tmpdir(), "background-output-"));
+    file = path.join(dir, "bg1.output");
+    published = [];
+  });
+
+  afterEach(async () => {
+    tail?.stop();
+    await rm(dir, { recursive: true, force: true });
+  });
+
+  it("replaces the terminal's output with the file's first text, then appends what the file adds", async () => {
+    await writeFile(file, "building\n");
+    follow();
+    await vi.waitFor(() => expect(published).toHaveLength(1), { timeout: 2000 });
+    await appendFile(file, "done\n");
+    await vi.waitFor(() => expect(published).toHaveLength(2), { timeout: 2000 });
+
+    expect(published).toEqual([
+      { text: "building\n", replaces: true },
+      { text: "done\n", replaces: false },
+    ]);
+  });
+
+  it("waits for a file that does not exist yet", async () => {
+    follow();
+    await new Promise((resolve) => setTimeout(resolve, 700));
+    expect(published).toEqual([]);
+
+    await writeFile(file, "started\n");
+    await vi.waitFor(() => expect(published).toHaveLength(1), { timeout: 2000 });
+    expect(published[0]).toEqual({ text: "started\n", replaces: true });
+  });
+
+  it("holds a character that a read splits until its last byte is written", async () => {
+    const check = Buffer.from("✓", "utf8");
+    await writeFile(file, check.subarray(0, 1));
+    follow();
+    await new Promise((resolve) => setTimeout(resolve, 700));
+    expect(published).toEqual([]);
+
+    await appendFile(file, check.subarray(1));
+    await tail!.finish();
+    expect(published).toEqual([{ text: "✓", replaces: true }]);
+  });
+
+  it("reads the rest of the file on finish, and nothing after", async () => {
+    await writeFile(file, "a");
+    follow();
+    await appendFile(file, "b");
+    await tail!.finish();
+    await appendFile(file, "c");
+    await new Promise((resolve) => setTimeout(resolve, 700));
+
+    expect(published.map((output) => output.text).join("")).toBe("ab");
+  });
+
+  it("sends at most the backlog, read by read, from the file's last bytes as a snapshot", async () => {
+    // More than the backlog, written faster than the polls read it.
+    const skipped = "x".repeat(BACKGROUND_OUTPUT_MAX_BACKLOG_BYTES);
+    const kept = "y".repeat(BACKGROUND_OUTPUT_MAX_BACKLOG_BYTES - 4) + "end\n";
+    await writeFile(file, skipped + kept);
+    follow();
+    await tail!.finish();
+
+    expect(published.map((output) => output.text).join("")).toBe(kept);
+    expect(published[0].replaces).toBe(true);
+    expect(published.slice(1).every((output) => !output.replaces)).toBe(true);
+    expect(
+      published.every((output) => Buffer.byteLength(output.text) <= BACKGROUND_OUTPUT_READ_BYTES),
+    ).toBe(true);
+  });
+
+  it("starts over with a snapshot when the file shrinks", async () => {
+    await writeFile(file, "old output\n");
+    follow();
+    await vi.waitFor(() => expect(published).toHaveLength(1), { timeout: 2000 });
+    await writeFile(file, "new\n");
+    await tail!.finish();
+
+    expect(published).toEqual([
+      { text: "old output\n", replaces: true },
+      { text: "new\n", replaces: true },
+    ]);
+  });
+
+  it("replaces the placeholder with an empty output when the command wrote nothing", async () => {
+    await writeFile(file, "");
+    follow();
+    await tail!.finish();
+
+    expect(published).toEqual([{ text: "", replaces: true }]);
+  });
+
+  it("publishes nothing on finish when the file never appeared", async () => {
+    follow();
+    await tail!.finish();
+
+    expect(published).toEqual([]);
+  });
+
+  it("reads nothing after stop", async () => {
+    follow();
+    tail!.stop();
+    await writeFile(file, "late\n");
+    await new Promise((resolve) => setTimeout(resolve, 700));
+
+    expect(published).toEqual([]);
+  });
+});
--- a/src/tests/claude-cli.test.ts
+++ b/src/tests/claude-cli.test.ts
@@ -0,0 +1,57 @@
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+// Fresh module state per test: the bundled CLI directory is process-wide.
+async function load() {
+  vi.resetModules();
+  return import("../claude-cli.js");
+}
+
+describe("claudeCliPath", () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = mkdtempSync(join(tmpdir(), "claude-cli-"));
+    vi.stubEnv("CLAUDE_CODE_EXECUTABLE", "");
+  });
+
+  afterEach(() => {
+    vi.unstubAllEnvs();
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  const cliFileName = process.platform === "win32" ? "claude.exe" : "claude";
+
+  it("prefers CLAUDE_CODE_EXECUTABLE over the bundled CLI", async () => {
+    const { claudeCliPath, useBundledClaudeCli } = await load();
+    writeFileSync(join(dir, cliFileName), "");
+    useBundledClaudeCli(dir);
+    vi.stubEnv("CLAUDE_CODE_EXECUTABLE", "/opt/claude");
+
+    expect(await claudeCliPath()).toBe("/opt/claude");
+  });
+
+  it("returns the CLI next to the executable", async () => {
+    const { claudeCliPath, useBundledClaudeCli } = await load();
+    writeFileSync(join(dir, cliFileName), "");
+    useBundledClaudeCli(dir);
+
+    expect(await claudeCliPath()).toBe(join(dir, cliFileName));
+  });
+
+  it("throws when the CLI is missing next to the executable", async () => {
+    const { claudeCliPath, useBundledClaudeCli } = await load();
+    useBundledClaudeCli(dir);
+
+    await expect(claudeCliPath()).rejects.toThrow(
+      `The Claude CLI is missing: expected ${join(dir, cliFileName)}. Keep ${cliFileName} from the release archive`,
+    );
+  });
+
+  it.skipIf(!process.env.RUN_INTEGRATION_TESTS)("finds the installed CLI", async () => {
+    const { claudeCliPath } = await load();
+    expect(await claudeCliPath()).toMatch(/@anthropic-ai\/claude-agent-sdk-[^/]+\/claude(\.exe)?$/);
+  });
+});
--- a/src/tests/clear-context-coordinator.test.ts
+++ b/src/tests/clear-context-coordinator.test.ts
@@ -28,6 +28,7 @@ function testSession(overrides: Partial<TestSession> = {}): TestSession {
      },
    },
    models: { currentModelId: "default" },
+    contextWindowSize: 200_000,
    configOptions: [],
    currentAgent: "default",
    fastModeEnabled: false,
@@ -464,6 +465,7 @@ describe("ExitPlanCoordinator", () => {
    expect(order).toEqual([
      "current_mode_update",
      "config_option_update",
+      "usage_update",
      ...(supportsPlanOperations
        ? [
            "plan_update " +
@@ -476,6 +478,10 @@ describe("ExitPlanCoordinator", () => {
        : []),
      "continuation",
    ]);
+    expect(host.sessionUpdate).toHaveBeenCalledWith({
+      sessionId: "public-session",
+      update: { sessionUpdate: "usage_update", used: 0, size: 200_000 },
+    });
    if (airClient) {
      expect(host.sessionUpdate).toHaveBeenCalledWith({
        sessionId: "public-session",
--- a/src/tests/context-compaction.test.ts
+++ b/src/tests/context-compaction.test.ts
@@ -4,6 +4,7 @@ import {
  ContextCompactionLifecycle,
  clientSupportsCompactionUpdates,
  compactionSummaryText,
+  contextCompactionMetadataFromBoundary,
  isCompactSummaryMessage,
 } from "../context-compaction.js";

@@ -635,3 +636,20 @@ describe("ContextCompactionLifecycle (tool_call)", () => {
    ]);
  });
 });
+
+describe("contextCompactionMetadataFromBoundary", () => {
+  /** An adapter-sent compaction is `idle` only when the CLI calls it manual; the CLI's own auto trigger stays `automatic`. */
+  it.each([
+    { cli: "manual", idleCompaction: false, expected: "manual" },
+    { cli: "manual", idleCompaction: true, expected: "idle" },
+    { cli: "auto", idleCompaction: true, expected: "automatic" },
+  ] as const)(
+    "reports $expected for a $cli boundary (idleCompaction: $idleCompaction)",
+    ({ cli, idleCompaction, expected }) => {
+      expect(
+        contextCompactionMetadataFromBoundary({ trigger: cli, pre_tokens: 1 }, { idleCompaction })
+          .trigger,
+      ).toBe(expected);
+    },
+  );
+});
--- a/src/tests/create-session-options.test.ts
+++ b/src/tests/create-session-options.test.ts
@@ -10,6 +10,7 @@ import type { AcpClient, ClaudeAcpAgent as ClaudeAcpAgentType } from "../acp-age
 import type { AcpSessionNotification } from "../acp-subagents.js";
 import { ALLOW_BYPASS } from "../permissions/modes.js";
 import { NativeSubagentRuntime } from "../native-subagents.js";
+import { startupFailure } from "./helpers.js";
 import * as fs from "node:fs";
 import * as os from "node:os";
 import * as path from "node:path";
@@ -321,6 +322,61 @@ describe("createSession options merging", () => {
    ).toBe(true);
  });

+  it("reports a worktree child's cwd from its SubagentStart hook, and none for a child in the session's cwd", async () => {
+    const updates: AcpSessionNotification[] = [];
+    const client = createMockClient();
+    client.sessionUpdate = async (notification) => {
+      updates.push(notification);
+    };
+    const observedAgent = new ClaudeAcpAgent(client);
+    await observedAgent.initialize({ protocolVersion: 1, clientCapabilities: { subagents: {} } });
+    const { sessionId } = await observedAgent.newSession({ cwd: process.cwd(), mcpServers: [] });
+    const session = observedAgent.sessions[sessionId]!;
+    const runtime = (session.nativeSubagentRuntime = new NativeSubagentRuntime(
+      "rfd",
+      sessionId,
+      session,
+      (notification) => client.sessionUpdate(notification),
+      { log: () => {} },
+    ));
+    const subagentStart = async (agentId: string, cwd: string) => {
+      const matcher = capturedOptions!.hooks!.SubagentStart!.find((matcher) => !matcher.matcher);
+      for (const hook of matcher!.hooks) {
+        await hook(
+          {
+            hook_event_name: "SubagentStart",
+            session_id: sessionId,
+            cwd,
+            transcript_path: "/tmp/transcript",
+            agent_id: agentId,
+            agent_type: "general-purpose",
+          },
+          undefined,
+          { signal: new AbortController().signal },
+        );
+      }
+    };
+    const worktree = path.join(process.cwd(), ".claude", "worktrees", "agent-isolated");
+    await subagentStart("isolated", worktree);
+    await subagentStart("shared", process.cwd());
+    await runtime.taskStarted(
+      { taskId: "isolated", subagentType: "general-purpose" },
+      async () => {},
+    );
+    await runtime.taskStarted(
+      { taskId: "shared", subagentType: "general-purpose" },
+      async () => {},
+    );
+    const announcements = updates.flatMap(({ update }) =>
+      update.sessionUpdate === "subagent_update" ? [update] : [],
+    );
+    expect(announcements).toMatchObject([
+      { sessionId: "isolated", cwd: worktree },
+      { sessionId: "shared" },
+    ]);
+    expect(announcements[1]).not.toHaveProperty("cwd");
+  });
+
  it("reports an AIR child's model switch under its current generation", async () => {
    const updates: AcpSessionNotification[] = [];
    const client = createMockClient();
@@ -1346,6 +1402,36 @@ describe("createSession options merging", () => {
    });
  });

+  describe("startup failures", () => {
+    it("asks Claude Code to report why it could not start", async () => {
+      await agent.newSession({ cwd: process.cwd(), mcpServers: [] });
+      expect(capturedOptions?.env?.CLAUDE_CODE_STARTUP_FAILURE_RESULTS).toBe("1");
+    });
+
+    it.each([
+      ["proxy_invalid", RequestError.internalError().code, "Internal error"],
+      ["gateway_signin_required", RequestError.authRequired().code, "Authentication required"],
+      ["org_pin_mismatch", RequestError.authRequired().code, "Authentication required"],
+      ["org_config_refused", RequestError.authRequired().code, "Authentication required"],
+      ["cwd_unavailable", RequestError.invalidParams().code, "Invalid params"],
+    ])("rejects with %s as code %i", async (reason, code, prefix) => {
+      initError = startupFailure(reason, "Fix the setting and restart Claude Code.");
+      await expect(agent.newSession({ cwd: process.cwd(), mcpServers: [] })).rejects.toMatchObject({
+        code,
+        message: `${prefix}: Fix the setting and restart Claude Code.`,
+        data: { startupFailureReason: reason },
+      });
+      expect(closeSpy).toHaveBeenCalled();
+    });
+
+    it("passes on an exit error that names no reason", async () => {
+      initError = new Error("Claude Code process exited with code 1. stderr: boom");
+      await expect(agent.newSession({ cwd: process.cwd(), mcpServers: [] })).rejects.toBe(
+        initError,
+      );
+    });
+  });
+
  describe("elicitation", () => {
    it("keeps AskUserQuestion disabled and omits callbacks without elicitation capability", async () => {
      await agent.initialize({ protocolVersion: 1, clientCapabilities: {} });
--- a/src/tests/diff-patch.test.ts
+++ b/src/tests/diff-patch.test.ts
@@ -466,6 +466,12 @@ describe("ACP v2 diffs", () => {
    );
  });

+  it("keeps a Windows path native in a git patch, so it matches the changes entry", () => {
+    expect(gitPatchText("C:\\work\\App.ts", "update", [hunk], "absolute")).toContain(
+      'diff --git "C:\\\\work\\\\App.ts" "C:\\\\work\\\\App.ts"\n--- "C:\\\\work\\\\App.ts"\n+++ "C:\\\\work\\\\App.ts"\n',
+    );
+  });
+
  it("shows no diff at tool use, where the input holds a snippet or no old text", () => {
    const renderer = new AcpToolCallRenderer(v2);
    const edit = { file_path: "/work/a.ts", old_string: "old", new_string: "new" };
--- a/src/tests/elicitation.test.ts
+++ b/src/tests/elicitation.test.ts
@@ -60,6 +60,19 @@ describe("mcpElicitationToCreateRequest", () => {
    });
  });

+  it("adds an empty properties map when the MCP schema has none", () => {
+    const request: ElicitationRequest = {
+      serverName: "server",
+      message: "Confirm?",
+      mode: "form",
+      requestedSchema: { type: "object" },
+    };
+
+    const result = mcpElicitationToCreateRequest(request, SESSION_ID);
+
+    expect(result).toMatchObject({ requestedSchema: { type: "object", properties: {} } });
+  });
+
  it("maps a url-mode request and preserves the elicitation id", () => {
    const request: ElicitationRequest = {
      serverName: "server",
@@ -119,6 +132,31 @@ describe("createElicitationResponseToElicitResult", () => {
    });
  });

+  it("forwards content values that only v2 allows, such as an object", () => {
+    // ACP v2 lets an elicitation value be any JSON value. The MCP server checks
+    // the content against its own schema, so none of it is dropped here.
+    const content = {
+      name: "Ada",
+      address: { city: "London" },
+      tags: ["a", 1, null],
+    };
+    const response = { action: "accept", content } as unknown as CreateElicitationResponse;
+    expect(createElicitationResponseToElicitResult(response)).toEqual({
+      action: "accept",
+      content,
+    });
+  });
+
+  it("maps accept content that is no JSON object to an empty object", () => {
+    for (const content of [null, "Ada", ["Ada"]]) {
+      const response = { action: "accept", content } as unknown as CreateElicitationResponse;
+      expect(createElicitationResponseToElicitResult(response)).toEqual({
+        action: "accept",
+        content: {},
+      });
+    }
+  });
+
  it("maps decline and cancel", () => {
    expect(
      createElicitationResponseToElicitResult({ action: "decline" } as CreateElicitationResponse),
@@ -343,6 +381,28 @@ describe("applyAskElicitationResponse", () => {
    });
  });

+  it("reads only string, number, and boolean picks from v2 content", () => {
+    // A v2 client may send an object or a mixed array. Such values are no
+    // option label, so they count as no pick instead of "[object Object]".
+    const response = {
+      action: "accept",
+      content: {
+        question_0: { label: "A" },
+        question_0_custom: { text: "ignored" },
+        question_1: ["X", { label: "Y" }, null, 2],
+      },
+    } as unknown as CreateElicitationResponse;
+
+    expect(applyAskElicitationResponse(response, toolInput, questions)).toEqual({
+      action: "answered",
+      updatedInput: {
+        questions,
+        metadata: { source: "test" },
+        answers: { "Multi?": "X, 2" },
+      },
+    });
+  });
+
  it("uses a multi-select question's custom answer alone when nothing is selected", () => {
    const response = {
      action: "accept",
@@ -639,10 +699,12 @@ describe("refusalFallbackResultFromResponse", () => {
      { action: "accept", content: { choice: "cancelled" } },
      { action: "accept", content: {} },
      { action: "accept", content: { choice: "something-new" } },
+      { action: "accept", content: { choice: { value: "retry_fallback" } } },
+      { action: "accept", content: { choice: ["retry_fallback"] } },
      { action: "accept" },
      { action: "decline" },
      { action: "cancel" },
-    ] as CreateElicitationResponse[];
+    ] as unknown as CreateElicitationResponse[];
    for (const response of cases) {
      expect(refusalFallbackResultFromResponse(response)).toBe("cancelled");
    }
--- a/src/tests/fast-mode-config.test.ts
+++ b/src/tests/fast-mode-config.test.ts
@@ -256,6 +256,31 @@ describe("setSessionConfigOption Fast mode toggle", () => {
    expect(response.configOptions).toContainEqual(createFastModeConfigOption(true, false));
  });

+  it("rejects a value whose type differs from the option's advertised type", async () => {
+    // Advertised as `type: "boolean"`: "on" is not a boolean.
+    const booleanClient = setup({ useBooleanOption: true });
+    await expect(
+      booleanClient.agent.setSessionConfigOption({
+        sessionId: SESSION_ID,
+        configId: FAST_MODE_CONFIG_ID,
+        value: FAST_MODE_ON,
+      }),
+    ).rejects.toMatchObject({ code: -32602 });
+    expect(booleanClient.applyFlagSettings).not.toHaveBeenCalled();
+
+    // Advertised as an on/off select: `true` is not a string.
+    const selectClient = setup({ useBooleanOption: false });
+    await expect(
+      selectClient.agent.setSessionConfigOption({
+        sessionId: SESSION_ID,
+        configId: FAST_MODE_CONFIG_ID,
+        type: "boolean",
+        value: true,
+      }),
+    ).rejects.toMatchObject({ code: -32602 });
+    expect(selectClient.applyFlagSettings).not.toHaveBeenCalled();
+  });
+
  it("does not change session state when the SDK rejects the flag", async () => {
    const { agent, applyFlagSettings } = setup({ useBooleanOption: true });
    applyFlagSettings.mockRejectedValueOnce(new Error("nope"));
--- a/src/tests/helpers.ts
+++ b/src/tests/helpers.ts
@@ -4,7 +4,11 @@
 * their own vi.fn spies via `overrides`.
 */

-import type { ClientCapabilities, InitializeRequest } from "@agentclientprotocol/sdk/unstable";
+import {
+  RequestError,
+  type ClientCapabilities,
+  type InitializeRequest,
+} from "@agentclientprotocol/sdk/unstable";

 /** The context-usage report the base mock query returns. `rawMaxTokens`
 *  matches the agent's DEFAULT_CONTEXT_WINDOW so window-related assertions
@@ -41,6 +45,19 @@ export function makeMockQuery(overrides: Record<string, unknown> = {}) {
  };
 }

+/**
+ * The error `initializationResult()` rejects with when Claude Code refuses to
+ * start with `CLAUDE_CODE_STARTUP_FAILURE_RESULTS` set, as SDK 0.3.316 builds
+ * it from the CLI's error result (same message prefix and fields).
+ */
+export function startupFailure(reason: string, cliMessage: string): Error {
+  return Object.assign(new Error(`Claude Code returned an error result: ${cliMessage}`), {
+    telemetryMessage: "Claude Code returned an error result",
+    errorClass: "error_result",
+    startupFailureReason: reason,
+  });
+}
+
 /**
 * Declares the client capabilities through `initialize`, as a real client
 * does. The agent reads its capability choices only there.
@@ -51,3 +68,16 @@ export async function initializeClient(
 ): Promise<void> {
  await agent.initialize({ protocolVersion: 1, clientCapabilities });
 }
+
+/**
+ * A request to a client that never answers it, as the SDK connection returns
+ * it with `stopWaitingOnCancel`: it rejects with `-32800` once `signal`
+ * aborts. The real connection also sends `$/cancel_request` then.
+ */
+export function heldRequest<T>(_params?: unknown, signal?: AbortSignal): Promise<T> {
+  return new Promise<T>((_resolve, reject) => {
+    const cancel = () => reject(RequestError.requestCancelled(signal?.reason));
+    if (signal?.aborted) cancel();
+    else signal?.addEventListener("abort", cancel, { once: true });
+  });
+}
--- a/Show More
+++ b/Show More