docs: update sprint-4 tracking - complete

docs/sprint-4.md

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+# Sprint 4: Code Review & Diff Viewing
+
+**Goal:** Review agent changes before merging.
+
+**Started:** 2026-01-26
+**Status:** Complete ✅
+
+---
+
+## Stories
+
+| ID | Title | Status | Notes |
+|----|-------|--------|-------|
+| US-401 | Diff viewer component | ✅ Complete | File tree + unified diff with syntax |
+| US-402 | Line-level comments | ✅ Complete | Click + to add inline comments |
+| US-403 | Approval workflow | ✅ Complete | Approve/Request Changes/Reject buttons |
+| US-404 | Merge and close | ✅ Complete | Merge button appears when approved |
+
+---
+
+## Progress Log
+
+### 2026-01-26
+
+**US-401: Diff viewer component** ✅
+- DiffViewer.tsx with file tree sidebar
+- Shows changed files with +/- counts
+- Click file to see unified diff
+- Hunk headers (@@ syntax)
+- Color-coded additions/deletions
+
+**US-402: Line-level comments** ✅
+- Click + button on any line to add comment
+- Inline textarea appears
+- Comments saved to task.reviewComments
+- Comments persist and display with yellow highlight
+
+**US-403: Approval workflow** ✅
+- ReviewPanel with three decision buttons
+- Approve (green), Request Changes (gray), Reject (red)
+- Decision saved to task.review state
+- Status banner shows decision + timestamp
+- Clear button to reset
+
+**US-404: Merge and close** ✅
+- "Merge & Close Task" button appears when approved
+- Confirmation dialog before merge
+- Merges branch, pushes, deletes worktree
+- Task status set to Done
+
+**Bug Fixes:**
+- Fixed `parseTaskFile` missing `review` field in return object
+- Fixed `useDebouncedSave` overwriting unchanged fields (now tracks changed fields only)
+
+---
+
+## Commits
+
+- `6fbbce0` feat(US-401): diff viewer component
+- `a210a2d` feat(US-402): line-level review comments
+- `44ff0d7` feat(US-403): approval workflow with review decisions
+- `ae94df4` feat(US-404): merge and close integration
+- `b4e4472` fix(US-403/404): review state sync bugs