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session/cancel dropped: "turnInterrupt failed: expected active turn id … but found …" #641
Description
Version: @agentclientprotocol/codex-acp 2.2.2, macOS. Seen 2026-10-14.
Client: fidget (ACP client). It sends session/cancel with the ACP sessionId while a session/prompt is in flight, then sends a new prompt soon after (cancels can come back-to-back).
Observed: the adapter logs Cancel - turnInterrupt failed: expected active turn id … but found …. The cancel is dropped. The in-flight prompt never resolves with stopReason: "cancelled" and keeps running until it ends on its own.
Expected: per ACP Prompt Turn / Cancellation, session/cancel should stop the active turn on that session and resolve the pending session/prompt with cancelled, whatever turn id the adapter tracks internally.
Suspected cause (not confirmed): the cancel path in CodexAcpServer looks up Codex's active turn id. That id can be out of date when a cancel races a turn starting or ending, so turnInterrupt is refused. Code: src/CodexAcpServer.ts at 5506fba. The only evidence so far is the log line above; we don't have a full log.
Repro idea: start a long prompt, send session/cancel right as a new turn begins (or cancel twice quickly), and watch for the log line.
Downstream: omesser/fidget#1529
— Cursor agent (P. Coder), on @omesser's behalf.
Activity
omesser commentedon Oct 18, 2026
Minimal repro on 2.2.2 (bundled codex 0.160.1), using a mock Responses provider and an ACP client, no login needed. Prompt,
session/cancelon the first chunk, wait forcancelled, prompt again, cancel again. The second cancel logsCancel - turnInterrupt failed: expected active turn id <new turn> but found <cancelled turn>, and that prompt runs toend_turn. A 2 s gap before the second prompt fails the same way.On 2.2.3-preview.14 both prompts come back
cancelled, which looks like the mismatch-retry change inrequestTurnInterrupt. Can this close when 2.2.3 ships?Downstream: omesser/fidget#1610
— Cursor agent (Coder), on @omesser's behalf.