docs(08-01): complete diff viewer plan

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.planning/phases/08-diff-viewer-download/08-01-SUMMARY.md

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+---
+phase: 08-diff-viewer-download
+plan: 01
+subsystem: ui
+tags: [react, diff-viewer, tanstack-query, tailwind]
+
+requires:
+  - phase: 07-config-history-ui
+    provides: ConfigHistorySection timeline component with ConfigChangeEntry data
+  - phase: 06-config-history-api
+    provides: GET /config/{snapshot_id}/diff endpoint returning DiffResponse
+provides:
+  - DiffViewer component with unified diff rendering (green/red line highlighting)
+  - configHistoryApi.getDiff() API client method
+  - Clickable timeline entries in ConfigHistorySection
+affects: [08-diff-viewer-download]
+
+tech-stack:
+  added: []
+  patterns: [inline diff viewer with line-level classification]
+
+key-files:
+  created:
+    - frontend/src/components/config/DiffViewer.tsx
+  modified:
+    - frontend/src/lib/api.ts
+    - frontend/src/components/config/ConfigHistorySection.tsx
+
+key-decisions:
+  - "DiffViewer rendered inline above timeline (not modal) for context preservation"
+  - "Line classification function for unified diff: +green, -red, @@blue, ---/+++ muted"
+
+patterns-established:
+  - "Inline viewer pattern: state-driven component rendered above list, closed via callback"
+
+requirements-completed: [UI-03]
+
+duration: 1min
+completed: 2026-03-13
+---
+
+# Phase 8 Plan 1: Diff Viewer Summary
+
+**Inline diff viewer with green/red line highlighting, wired into clickable config history timeline entries**
+
+## Performance
+
+- **Duration:** 1 min
+- **Started:** 2026-03-13T04:19:53Z
+- **Completed:** 2026-03-13T04:20:56Z
+- **Tasks:** 2
+- **Files modified:** 3
+
+## Accomplishments
+- DiffViewer component renders unified diffs with color-coded lines (green additions, red removals, blue hunk headers)
+- API client getDiff method fetches diff data from backend endpoint
+- Timeline entries in ConfigHistorySection are clickable with hover states
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Add diff API client and create DiffViewer component** - `dda00fb` (feat)
+2. **Task 2: Wire DiffViewer into ConfigHistorySection timeline entries** - `2cf426f` (feat)
+
+## Files Created/Modified
+- `frontend/src/components/config/DiffViewer.tsx` - Unified diff viewer with line-level color highlighting, loading skeleton, error state
+- `frontend/src/lib/api.ts` - Added DiffResponse interface and configHistoryApi.getDiff() method
+- `frontend/src/components/config/ConfigHistorySection.tsx` - Added click handlers, selectedSnapshotId state, inline DiffViewer rendering
+
+## Decisions Made
+- Rendered DiffViewer inline above the timeline rather than in a modal, preserving context
+- Used a classifyLine helper function for clean line-type detection (handles +++ and --- separately from + and -)
+- Loading skeleton uses randomized widths for visual variety
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Diff viewer complete, ready for config download functionality (plan 08-02)
+- All TypeScript compiles cleanly
+
+---
+*Phase: 08-diff-viewer-download*
+*Completed: 2026-03-13*