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Ouyang Xingyuan
c17e7c5b64
Cancelling a foreground turn can leave two owners of "is a turn running". The manager force-cancels after its 2 s settle window: it synthesizes turn_canceled and reports the agent idle. The provider session never confirmed that turn ended, so it still holds the slot. Every later prompt then fails with "A foreground turn is already active" until the agent is reloaded. ACP is the reproducible case. ACPAgentSession.interrupt() sends session/cancel, which is a notification: it resolves as soon as it is written. An agent that answers cancelled but keeps working in the same process, or never answers at all, leaves activeForegroundTurnId set. This is the failure observed locally on 2026-10-20 with a droid-magpie agent: five "[System Error] A foreground turn is already active" rows and no way to send anything afterwards. Add AgentSession.abandonForegroundTurn? as the seam for that state. The manager calls it after a forced settlement, and only then; a cancel that settles keeps today's path. A provider that implements it must make the session usable again rather than clear a local flag, because reusing a runtime that may still be working is the split-brain shape docs/agent-lifecycle.md forbids. wrapSessionProvider forwards the hook. Without that line the manager only sees the wrapper's fixed member list, so an optional method added to the interface is silently dropped for every wrapped provider. The ACP adapter kills the process that owned the abandoned turn, drops the slot, and synthesizes cancelled tool calls for rows that were still running. Its next startTurn resumes the durable session in a new process and drops the replayed history rows, since the daemon already has them. A kill-timeout rejects, which leaves the agent as it was. Tests: a force-canceled turn releases the session and the next prompt starts, a settled cancel does not call the hook, a rejected release still settles, the wrapper forwards the hook or omits it, and the ACP adapter reconnects on the next turn without replaying history twice.