## Summary
- detect persisted executor sessions that cannot continue from an
assistant message
- clear the stale session pointer after the executor lock is released
- requeue the task with workflow progress preserved instead of marking
it failed
## Test plan
- `pnpm --filter @fusion/engine exec vitest run
src/__tests__/executor-step-session.test.ts -t "clears a stale
assistant-continuation resume session and requeues without marking the
task failed" --project=engine-default --silent=passed-only
--reporter=dot`
- `pnpm --filter @fusion/engine typecheck`
- `pnpm build`
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Improved recovery when an assistant continuation session becomes stale
by restarting a fresh session with bounded retries, preserving overall
task progress.
* Clears invalid persisted session/continuation state and defers requeue
until coordination cleanup is safe.
* When retries are exhausted, tasks are marked failed and the error
callback runs (without routing to review).
* **Tests**
* Added coverage for stale-session recovery, repeated-stale behavior,
correct (or skipped) requeue decisions, and progress/error handling
paths.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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