d83f28a403
Found while reviewing #1226: a prompt that `session/cancel` reports as cancelled still runs in Claude Code. It affects ACP v1 and v2. ## Problem `cancel()` settles every queued prompt as `cancelled`, but each was already pushed to Claude Code. Claude Code keeps queued messages through an interrupt and runs them next. The SDK documents the interrupt receipt's `still_queued` as "messages that WILL still run unless cancelled first". So: - Claude Code answers prompts the client was told were cancelled, and they stay in the conversation, and in the model's context, for later turns. - The orphan accounting skips their results, and a cancelled session drops consolidated `assistant` frames, but their streamed deltas still reach the client after the cancel. - In v2 (#1226), such a prompt is answered `-32800` ("not inserted"), then its output arrives anyway. ## Change `cancel()` now sends `cancel_async_message` for each queued message it abandons, before the interrupt. That covers queued prompts and pending steers. This is the pattern the SDK's own docs describe for a wrapper that wants per-uuid control, rather than `cancel_queued` on the interrupt, which would also sweep a prompt the client sends right after the cancel. - **Before the interrupt**, because once the interrupt stops the running turn, Claude Code starts the next queued message right away. - **Not awaited.** The SDK writes control requests to Claude Code in call order, so the drops still arrive before the interrupt, and a wedged CLI can't hold up the cancel, or the teardown that uses it. - **No new accounting.** A dropped message gets a `cancelled` lifecycle frame and is missing from the interrupt receipt's `still_queued`, and the orphan accounting already handles both. - **Residual window:** a message Claude Code had already dequeued, or one the SDK hadn't written yet, still runs as an orphan, exactly as before. The SDK implements the request as `Query.cancelAsyncMessage` (0.3.287) but doesn't type it, so it's looked up. A mocked query without it skips the drop. A CLI that doesn't know the request rejects it, which is logged. ## Testing A new test in `src/tests/turn-events.test.ts` scripts Claude Code's queue: a queued prompt runs after the interrupt unless it was dropped first, as the real CLI does. It asserts: - the drop goes out before the interrupt; - the queued turn ends `cancelled`; - the cancelled prompt's answer never reaches the client. Without the drop, the test fails with the leaked answer (`chunk Answer to a cancelled prompt` after `first ended cancelled`). Sending the drop after the interrupt also fails it. The rest of the suite passes unchanged. `npm run build`, `npm run check`, `npm run test:run` (2243 passed).
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
Subagents are exposed only after bilateral capability negotiation. Until the released ACP SDKs
preserve the draft clientCapabilities.subagents field, a supporting client may advertise
nativeSubagentSessions in _meta.jetbrains.air.capabilities; the adapter mirrors the capability
in its initialize response. The canonical field remains supported and takes precedence once it is
available. Without either client signal, Agent/Task lifecycle keeps its legacy ordinary ACP
tool-call representation and child interactions stay on the root session. Clients that use the
historical _meta["subagent-transcript"] capability or forwardSubagentText session option retain
the flattened child transcript behavior. See AIR extensions.
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).