feat(refinery): implement merge failure handling with labels and notifications
Add comprehensive failure handling for merge queue:
- Add FailureType enum with conflict, tests_fail, build_fail, flaky_test, push_fail
- Add handleFailure function that updates beads issue with labels and assignee
- Add notifyWorkerFailure for type-specific failure notifications
- Add retry logic for flaky tests (configurable via retry_flaky_tests)
- Add pushWithRetry with exponential backoff for transient push failures
- Add label support to beads UpdateOptions (AddLabels, RemoveLabels, SetLabels)
Failure actions by type:
- conflict: needs-rebase label, assign to worker
- tests_fail/build_fail: needs-fix label, assign to worker
- flaky_test: retry once, then treat as tests_fail
- push_fail: retry with backoff, needs-retry label
Closes gt-3x1.4
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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