Implements Option A from the issue: multiple refinery workers with locking.
Changes to mrqueue:
- Add ClaimedBy/ClaimedAt fields to MR struct
- Add Claim(id, worker) method with atomic file operations
- Add Release(id) method to unclaim on failure
- Add ListUnclaimed() to find available work
- Add ListClaimedBy(worker) for worker-specific queries
- Claims expire after 10 minutes for crash recovery
New CLI commands:
- gt refinery claim <mr-id> - Claim MR for processing
- gt refinery release <mr-id> - Release claim back to queue
- gt refinery unclaimed - List available MRs
Formula updates:
- queue-scan now uses gt refinery unclaimed
- process-branch claims MR before processing
- handle-failures releases claim on test failure
- Claims prevent double-processing by parallel workers
Worker ID comes from GT_REFINERY_WORKER env var (default: refinery-1).
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>