Implement success handling for the merge queue Engineer:
- Add handleSuccess method that handles successful merge completion
- Update MR body with merge_commit SHA and close_reason
- Close MR with 'merged' reason
- Close source issue with reference to MR ID
- Delete source branch if delete_merged_branches is configured
- Add DeleteRemoteBranch method to git package
- Add git client to Engineer struct
- Add tests for new functionality
Closes gt-3x1.5
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Adds the Engineer component that polls for ready merge-requests and
processes them according to the merge queue design.
Features:
- Main loop that queries `bd ready` for merge-request type issues
- Configurable poll_interval and max_concurrent from rig config.json
- Graceful shutdown via context cancellation or Stop() method
- Claims MRs via `bd update --status=in_progress` before processing
- Handles success/failure with appropriate status updates
Configuration (in rig config.json merge_queue section):
- poll_interval: duration string (default "30s")
- max_concurrent: number (default 1)
- enabled, target_branch, run_tests, test_command, etc.
Also adds ReadyWithType() to beads package for type-filtered queries.
Note: ProcessMR() and handleFailure() are placeholders - full
implementation in gt-3x1.2 and gt-3x1.4.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
