GAP-TOOLS-030: Effect Cancellation

Description

Cancel or stop a running effect mid-execution. CC's TaskStopTool can cancel background tasks. Babysitter has no cancellation mechanism -- once an effect is dispatched, it runs to completion or timeout.

Current State

Effects are dispatched via ctx.task() and executed by the harness operator. BABYSITTER_TIMEOUT (default 2min) and BABYSITTER_NODE_TASK_TIMEOUT (15min) are the only guards. The invokeHarness() function spawns a child process with a timeout but the operator cannot cancel individual effects. If a harness hangs, the entire run blocks until timeout.

No journal event for cancellation. No EFFECT_CANCELLED type.

Target State

``javascript try { await ctx.task(longRunningTask, args); } catch (e) { if (e instanceof EffectCancelledError) { // handle graceful cancellation } } ``

• New EFFECT_CANCELLED journal event type
• task:cancel <runId> <effectId> CLI command
• Cancel signal propagated to running harness process (SIGTERM then SIGKILL)
• Effect result marked as status: 'cancelled' with cancellation reason
• Process code receives cancellation as a thrown error that can be caught:
• Embedded SDK dashboard shows cancel button for running effects
• Timeout-based auto-cancellation configurable per task

Dependencies

None (core cancellation is standalone).

**Optional enhancement**: GAP-SUBOBS-004 -- health monitoring can trigger auto-cancel (future integration, not a prerequisite)

Key Files

Recommendation

Phase 2. High priority for production use -- runaway effects are a real operational issue. Start with CLI cancellation, then add embedded SDK dashboard button.