story-kit: done 238_story_mergemaster_handles_merge_conflicts_by_resolving_them_automatically

.story_kit/work/5_done/238_story_mergemaster_handles_merge_conflicts_by_resolving_them_automatically.md

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+---
+name: "Mergemaster handles merge conflicts by resolving them automatically"
+---
+
+# Story 238: Mergemaster handles merge conflicts by resolving them automatically
+
+## User Story
+
+As a mergemaster agent, I want to detect and resolve merge conflicts when squash-merging feature branches, so that stories don't get stuck in the merge queue requiring manual intervention.
+
+## Acceptance Criteria
+
+- [ ] When merge_agent_work encounters a merge conflict, the mergemaster reads both sides of the conflict and produces a resolved file that preserves changes from both branches
+- [ ] After resolving conflicts, the mergemaster runs quality gates (cargo check, cargo test, pnpm build, pnpm test) to verify the resolution is correct
+- [ ] If quality gates fail after conflict resolution, the merge is reported as failed with details about what went wrong
+- [ ] The mergemaster handles the common case of multiple feature branches adding to the same file (e.g. both adding tests or UI sections to the same component)
+
+## Context
+
+Three stories got stuck in the merge queue (2026-02-28) because the mergemaster couldn't handle conflicts:
+
+- Stories 235, 236, 237 all modified the same files (`WorkItemDetailPanel.tsx` and its test file)
+- 237 merged cleanly. 235 failed silently (empty output from `merge_agent_work`). 236 had conflicts in both component and test files.
+
+**Conflict patterns observed:**
+1. **add/add in test file**: Multiple branches created the same test file from scratch with different mock setups. Resolution: combine mock setups and keep all test suites.
+2. **content conflict in component**: Both branches added different state, imports, hooks, and UI sections. Resolution: keep all additions from both sides.
+3. **Placeholder list divergence**: Both branches removed different items from a shared placeholder list. Resolution: remove both since both features are now real.
+
+**Manual resolution process:**
+1. `git merge --squash --no-commit feature/story-{id}`
+2. Read conflicted files, understand both sides
+3. Write resolved files combining both feature additions
+4. Run `tsc --noEmit` and `pnpm test` to verify
+5. Stage, commit, move story to done
+
+Most conflicts in this codebase are additive — two branches adding different features to the same files, not contradictory changes.
+
+## Out of Scope
+
+- TBD