When the Refinery detects a build error or test failure and refuses
to merge, the polecat was never notified. This fixes the notification
pipeline by:
1. Adding MERGE_FAILED protocol support to Witness:
- PatternMergeFailed regex pattern
- ProtoMergeFailed protocol type constant
- MergeFailedPayload struct with all failure details
- ParseMergeFailed parser function
- ClassifyMessage case for MERGE_FAILED
2. Adding HandleMergeFailed handler to Witness:
- Parses the failure notification
- Sends HIGH priority mail to polecat with fix instructions
- Includes branch, issue, failure type, and error details
3. Adding mail notification in Refinery's handleFailureFromQueue:
- Creates mail.Router for sending protocol messages
- Sends MERGE_FAILED to Witness when merge fails
- Includes failure type (build/tests/conflict) and error
4. Adding comprehensive unit tests:
- TestParseMergeFailed for full body parsing
- TestParseMergeFailed_MinimalBody for minimal body
- TestParseMergeFailed_InvalidSubject for error handling
- ClassifyMessage test cases for MERGE_FAILED
Fixes#114🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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