When a user cancels a generation (ESC x2), all three idle hooks could
enter a permanently broken state:
1. **todo-continuation-enforcer**: consecutiveFailures accumulated from
abort-caused promptAsync failures, eventually hitting MAX_CONSECUTIVE_FAILURES
and permanently stopping continuation injection.
2. **unstable-agent-babysitter**: no abort awareness at all — would keep
firing reminders after user cancelled the session.
3. **runtime-fallback**: retry dedupe keys and pending fallback state
persisted across cancellation, blocking legitimate error recovery.
Fix:
- Add shared `isAbortError()` utility for consistent abort detection
- Reset consecutiveFailures and clear stale state on AbortError in all hooks
- Track `lastCancelledAt` in todo-continuation-enforcer for abort window
- Add abort-awareness to unstable-agent-babysitter (skip if recently cancelled)
- Clear runtime-fallback retry state on abort errors
Tests: 61 pass, 0 fail across all 3 affected hook test suites.
Closes#2984
YeonGyu-Kim