huskies: create 498_bug_stale_merge_job_lock_prevents_new_merges_after_agent_dies

.huskies/work/1_backlog/498_bug_stale_merge_job_lock_prevents_new_merges_after_agent_dies.md

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+---
+name: "Stale merge job lock prevents new merges after agent dies"
+---
+
+# Bug 498: Stale merge job lock prevents new merges after agent dies
+
+## Description
+
+When the mergemaster agent is killed or stops while a merge is in progress, the in-memory `merge_jobs` map retains a `Running` status entry for that story. Subsequent attempts to call `merge_agent_work` get "Merge already in progress" and fail. The lock is never cleaned up.
+
+This causes the mergemaster to loop: spawn, try merge, get "already in progress", waste turns, exit, respawn. The merge never completes.
+
+The fix: clear the merge job entry when the mergemaster agent exits (whether cleanly or via kill/stop).
+
+## How to Reproduce
+
+1. Start mergemaster on a story in merge
+2. Kill/stop the mergemaster agent before merge completes
+3. Try to merge_agent_work again for the same story
+4. Get "Merge already in progress" error
+
+## Actual Result
+
+Stale Running entry in merge_jobs map blocks all future merge attempts until server restart.
+
+## Expected Result
+
+Merge job lock is cleaned up when the agent exits, allowing retry.
+
+## Acceptance Criteria
+
+- [ ] Bug is fixed and verified