b4788d61ea
On v1, when a cancel stops a model cycle that Claude Code started on its own, the cycle's open tool calls now end. Before, they stayed `pending` for good. ## The bug Example, from a live run (Claude Code 2.1.296, a v1 client): 1. A prompt starts a background command, and its turn ends. 2. The command finishes, and Claude Code starts a cycle on its own: it launches a foreground subagent, which runs a command. 3. The client sends `session/cancel` while no prompt runs. Claude Code stops both and sends the Agent call's interrupted result (`user-rejected`). The client never got it, and the Agent call stayed `pending`. Before #1336, the subagent's command stayed `pending` too. **Why:** the window after a cancel drops output once the client has been told that the stopped work ended (#1313). On v1 that report is the prompt response, read as "no active turn". A cycle never has a turn, so from the cancel on, everything it sent counted as late output, including Claude Code's results for its own tool calls. v2 tracks a cycle as foreground work and closes its calls before `idle cancelled` (#1339). v1 tracked nothing. ## The fix - **The agent tracks foreground work on every connection.** Only v2 reports it, through the `foreground` option; v1 gets events that do nothing (`UNREPORTED_FOREGROUND`). The rules for when a cycle starts and ends are the ones v2 already uses. - **On v1, a cycle's end is its result or its idle** (`workEndReported`). Until then, Claude Code's interrupted results reach the client. At that end, `closeCancelledCycleToolCalls` closes the calls that got none, as on v2. After it, the window drops what comes, as before. A v1 turn's rule is unchanged: no active turn. - **A held turn's follow-up shares the held turn's closing.** v1 holds a turn for its background subagents, and the held turn's follow-up is a cycle too, now on v1 as well. When a second cancel settled the held turn in `cancelTurns` while the cycle's closing was in flight, the two ran separate passes. The response then came before the cycle's first report, and on v2 a call could be closed twice. `closeCancelledCycleToolCalls` now uses the held turn's closing (`Turn.closingCancelledToolCalls`), which every settle of the turn waits for. The existing test "closes each tool call once, before the response, when a cancel settles a held turn that the consumer is closing" caught this. ## Evidence **Live, Claude Code 2.1.296, the scenario above**, every update checked against the schema (no violations): | Client | Agent call | Subagent's command | |---|---|---| | v1, before | `pending` | `failed` (closed by #1336) | | v1, this PR | `failed`, with Claude Code's own `user-rejected` result | `failed`, closed at the cycle's end | | v1 RFD client, this PR | the same | the same, in the child's session | | v2, this PR | `cancelled`, before `idle cancelled` | `cancelled`, before `idle cancelled` (unchanged) | A v1 cancel with a queued prompt, followed by the next prompt, still left no tool call open, and the next prompt's Write asked for its permission and ran. **Tests** (`src/tests/incomplete-tools.test.ts`): - **#1339's test for v1 now asserts the fix:** a cycle's command gets Claude Code's interrupted result. - **New:** the live scenario, where the Agent call gets Claude Code's result and the subagent's command is closed; and a cycle that ends at an idle with no result, where its call is closed at the idle and Claude Code's later result is dropped. - **#1336's "no turn" fixture** launched the background subagents in a cycle it never ended before the cancel, so v1 now delivered Claude Code's real result there. The fixture now ends that cycle, which is the "cancel while nothing runs" case the tests mean. - **Mutation checks:** each of these fails at least one test: - the v1 rule without the cycle; - no cycles on v1; - no foreground tracking on v1; - a separate closing for a held turn's follow-up. `npm run check`, build and the full suite (2979 tests) pass, with no golden changes. ## Not covered - A cycle that ends normally with a `tool_use` that Claude abandoned keeps that call open. - A subagent that completes after a cancel keeps its calls open.
ACP adapter for the Claude Agent SDK
Use Claude Agent SDK from ACP-compatible clients!
This tool implements an ACP agent by using the official Claude Agent SDK, supporting:
- Context @-mentions
- Images
- Tool calls (with permission requests)
- Compact file changes through the negotiated AIR diff patch extension
- Following
- Edit review
- TODO lists
- Nested subagent transcripts
- Interactive (and background) terminals
- Custom Slash commands
- Client MCP servers
/mcpin the chat: the MCP server status as a list. The adapter runs/mcp reconnect,/mcp enable, and/mcp disablethrough the SDK control API, because Claude Code refuses them in SDK mode. A reconnect of an ACP server that needs authentication starts MCP OAuth through URL elicitation- Session-scoped long-running goals for AIR through the goal extension under
_meta.jetbrains.air.goal - Structured errors, recovery, and warnings through the opt-in session failure extension
- Concrete model and effort defaults through the opt-in recommended config value extension
- Tool permission presentation, editable choices, and durable effects through the permission extension
- One fact per field in every tool call report, as the ACP tool call contract defines
- All AIR extensions, capabilities, and
_metakeys: AIR extensions
Learn more about the Agent Client Protocol.
To try changes that have landed on main but are not released yet, install from the
preview channel — every push to main publishes one. See
docs/RELEASES.md.
npm install @agentclientprotocol/claude-agent-acp@preview
Subagent sessions
A client that declares clientCapabilities.subagents, other than JetBrains AIR, gets each Agent or
Task subagent as its own child session, following the subagents RFD:
subagent_updateon the parent announces the child before any of its traffic, with the parent'stitleanddescriptionfor it, and reports its work state:running,requires_actionwhile one of its requests is open (andrunningagain when the last one ends, unless a cancel withdrew it: the child is stopping then), andidlewhen its work ends, withend_turnorcancelledwhen the SDK gives the reason. A failure isidlewith theerrorstop reason and the SDK's error text as itserror. The child keeps its session for every delegation to it.- The prompt of the Agent or Task call that launches the child, and the message of each
SendMessage call that resumes it, is a
session_messagein the child's transcript. The tool call stays a tool call of the session that made it. session/cancelon the parent interrupts Claude Code, which stops the foreground children that the turn waits on and, currently, background children too. Each stopped child reportsidlewithcancelledfrom Claude Code's own events, and the open requests of the foreground ones are withdrawn. The adapter ends no child at a cancel itself, so a child that keeps running keeps its open requests and its open tool calls. A tool call of a stopped child that Claude Code reports no result for, such as the command it was running, ends in the child's session before the cancelled prompt resolves. When Claude Code stops a background child after that, or while no prompt runs, the tool call ends right after the child reportsidle. A child that still runs when Claude Code exits isidlewith no stop reason.- A child whose parent is not yet known when it ends is not exposed, since the RFD forbids guessing its parent.
- A replay restores each child under its live session id, from its own transcript: its prompt and
each SendMessage message are
session_messages, and its end is anidlebefore the response. A launch without Claude Code's metadata file for the child stays an ordinary tool call of the parent, and a notice, for a client that takes notices, says that subagent history is missing. - After a load or resume, with or without replay, a SendMessage that resumes an agent from before it runs that agent in its session from before. Before the agent's traffic, each of its ancestors that the client was not told about in this connection is announced, parent before child and with no work state, as the RFD requires. An agent whose launch the session's history does not record stays unexposed.
- A client cannot prompt, cancel, or otherwise change a child yet.
An ACP v2 client gets the same without declaring anything, since subagents
are part of v2's baseline. Each child also reports its work state as its own state_update, right
after the parent's copy.
JetBrains AIR keeps the earlier draft of the RFD (subagent_spawned, subagent_state_update),
which it enables with nativeSubagentSessions in _meta.jetbrains.air.capabilities. See
AIR extensions.
Without either signal, Agent and Task stay ordinary tool calls and child interactions stay on the
root session. Clients that use the historical _meta["subagent-transcript"] capability or the
forwardSubagentText session option retain the flattened child transcript.
Experimental ACP v2
Started with CLAUDE_AGENT_ACP_EXPERIMENTAL_V2=1, the adapter also serves the
draft ACP v2: a client that asks for
protocol version 2 or later in initialize gets v2, and every other client gets v1, as before.
The draft can still change, and this surface changes with it.
On v2 the adapter serves the session baseline (session/new, session/list, session/resume
with replay, session/close, session/prompt, session/cancel), session/delete,
session/fork, additional directories, config options (the mode is one), plans, notices,
compaction, display terminals for commands, permission requests, elicitation, providers, auth, and
subagents. Steering and the AIR extensions are v1 only for now.
Contribution Policy
This project does not require a Contributor License Agreement (CLA). Instead, contributions are accepted under the following terms:
By contributing to this project, you agree that your contributions will be licensed under the Apache License, Version 2.0. You affirm that you have the legal right to submit your work, that you are not including code you do not have rights to, and that you understand contributions are made without requiring a Contributor License Agreement (CLA).