docs(12-01): complete comparison view plan

- ComparisonTable component with 10 attribute rows and sticky label column
- Delta highlighting: blue-50 lightest weight, green-50 cheapest price, gray delta text
- Compare toggle in thread detail toolbar (visible for 2+ candidates)
- All COMP-01 through COMP-04 requirements marked complete

.planning/phases/12-comparison-view/12-01-SUMMARY.md

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+---
+phase: 12-comparison-view
+plan: "01"
+subsystem: ui
+tags: [react, tailwind, comparison-table, zustand, framer-motion]
+
+# Dependency graph
+requires:
+  - phase: 11-candidate-ranking
+    provides: RankBadge component and sort_order-based candidate ordering
+  - phase: 10-schema-foundation-pros-cons-fields
+    provides: pros/cons fields on CandidateWithCategory type
+provides:
+  - ComparisonTable component with sticky label column and horizontal scroll
+  - candidateViewMode "compare" value in uiStore
+  - Compare toggle in thread detail toolbar (visible when 2+ candidates)
+  - Weight/price delta highlighting with best-cell color coding
+  - Resolved thread winner column marking (amber tint + trophy)
+affects: [future comparison features, thread detail enhancements]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - Declarative ATTRIBUTE_ROWS array pattern for table row rendering (key, label, render, cellClass)
+    - useMemo delta computation for best-cell identification in comparison views
+
+key-files:
+  created:
+    - src/client/components/ComparisonTable.tsx
+  modified:
+    - src/client/stores/uiStore.ts
+    - src/client/routes/threads/$threadId.tsx
+
+key-decisions:
+  - "ATTRIBUTE_ROWS declarative array pattern keeps JSX clean and row reordering trivial"
+  - "cellClass function pattern in ATTRIBUTE_ROWS allows per-row cell styling without duplicating winner-check logic in every render"
+  - "Compare toggle only shown when >= 2 candidates (locked decision from plan)"
+  - "Add Candidate button hidden in compare view — compare is for reading, not mutation"
+  - "Winner highlight priority: weight/price color wins over amber tint when both apply (more informative)"
+
+patterns-established:
+  - "Declarative table row config: ATTRIBUTE_ROWS array with { key, label, render, cellClass } objects"
+  - "Sticky left column pattern: sticky left-0 z-10 bg-white on every label cell for scroll bleed prevention"
+
+requirements-completed: [COMP-01, COMP-02, COMP-03, COMP-04]
+
+# Metrics
+duration: 2min
+completed: 2026-03-17
+---
+
+# Phase 12 Plan 01: Comparison View Summary
+
+**Side-by-side candidate comparison table with sticky labels, weight/price delta highlighting, and resolved-thread winner marking via a new "compare" candidateViewMode**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-03-17T14:28:12Z
+- **Completed:** 2026-03-17T14:30:00Z
+- **Tasks:** 2
+- **Files modified:** 3
+
+## Accomplishments
+- Built ComparisonTable component with 10 attribute rows (Image, Name, Rank, Weight, Price, Status, Link, Notes, Pros, Cons) using declarative ATTRIBUTE_ROWS pattern
+- Implemented useMemo delta computation — lightest weight cell highlighted blue-50, cheapest price cell green-50, non-best cells show gray +delta string
+- Sticky left column with bg-white prevents content bleed-through on horizontal scroll
+- Amber tint + trophy icon on winner column in resolved threads; weight/price color takes priority when winner is also best
+- Extended uiStore candidateViewMode to "list" | "grid" | "compare" and wired compare toggle in thread detail toolbar
+- Compare toggle only appears when thread has 2+ candidates; Add Candidate button hidden in compare view
+- All 135 existing tests pass, no regressions
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Build ComparisonTable component** - `e442b33` (feat)
+2. **Task 2: Wire compare toggle and ComparisonTable into thread detail** - `5b4026d` (feat)
+
+## Files Created/Modified
+- `src/client/components/ComparisonTable.tsx` - New comparison table component with all 10 attribute rows, delta computation, sticky labels, and winner highlighting
+- `src/client/stores/uiStore.ts` - Extended candidateViewMode union to include "compare"
+- `src/client/routes/threads/$threadId.tsx` - Added ComparisonTable import, compare toggle button (columns-3 icon), ComparisonTable rendering branch, and "Add Candidate" hidden in compare view
+
+## Decisions Made
+- ATTRIBUTE_ROWS declarative array pattern keeps table JSX clean and row reordering trivial — each row is just { key, label, render, cellClass }
+- cellClass function in ATTRIBUTE_ROWS allows per-row cell styling without duplicating winner-check logic in every render function
+- Compare toggle only shown for 2+ candidates per locked plan decision
+- Add Candidate button hidden in compare view to keep toolbar uncluttered (users switch to list/grid to add)
+- When winner IS also the lightest/cheapest, weight/price color (blue/green) takes priority over amber tint — more informative
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+- Minor formatting differences caught by Biome auto-formatter (indentation depth in conditional JSX) — resolved with `biome check --write`. No logic changes.
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- ComparisonTable is complete and functional; compare mode wired end-to-end in thread detail
+- No blockers — ready for any follow-on comparison view enhancements
+- All existing tests pass; no backend changes needed
+
+---
+*Phase: 12-comparison-view*
+*Completed: 2026-03-17*