docs(08-03): complete renderTrackRow optimization plan

- SUMMARY.md with classMap directive migration results - STATE.md updated: 3/4 plans complete, decisions recorded - ROADMAP.md updated with plan progress
2026-03-04 23:24:15 -05:00
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+---
+phase: 08-frontend-performance-ux
+plan: 03
+subsystem: frontend
+tags: [lit, classMap, performance, render-optimization, directives]
+
+# Dependency graph
+requires:
+  - phase: 08-frontend-performance-ux
+    provides: "repeat() directive migration on all virtualizer instances"
+provides:
+  - "classMap directive for conditional CSS classes in track-list renderTrackRow and queue-panel renderTrackItem"
+  - "Search highlight short-circuit when search term is empty"
+  - "Hoisted search term lookup outside per-column iteration loop"
+affects: [08-frontend-performance-ux]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: ["classMap directive for conditional CSS classes in render hot paths"]
+
+key-files:
+  created: []
+  modified:
+    - frontend/src/components/track-list/track-list.ts
+    - frontend/src/components/queue-panel/queue-panel.ts
+
+key-decisions:
+  - "classMap object literal per-call is acceptable — classMap internally diffs and only updates changed classes"
+  - "Hoisted searchCtrl.term outside cols.map to avoid repeated property access per column"
+
+patterns-established:
+  - "Render hot path pattern: use classMap directive instead of array filter/join for conditional CSS classes"
+
+requirements-completed: [PERF-05, UX-02]
+
+# Metrics
+duration: 2min
+completed: 2026-03-05
+---
+
+# Phase 8 Plan 03: renderTrackRow Optimization Summary
+
+**Replaced array filter/join class construction with classMap directive in track-list and queue-panel render hot paths, eliminating per-row array allocations during scrolling**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-03-05T04:19:55Z
+- **Completed:** 2026-03-05T04:22:19Z
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- All conditional CSS class construction in renderTrackRow (track-row, fav-icon, cell) converted from array filter/join to classMap directive
+- Queue-panel renderTrackItem class construction (track-item, active, selected, drop-before, drop-after) converted to classMap
+- Search term property lookup hoisted outside per-column loop to avoid repeated access
+- Search highlighting already short-circuits when term is empty — no additional optimization needed
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Replace class string construction with classMap directive in renderTrackRow** - `ad21027` (perf)
+2. **Task 2: Optimize column value computation and apply classMap to queue-panel renderTrackItem** - `62f41c2` (perf)
+
+## Files Created/Modified
+- `frontend/src/components/track-list/track-list.ts` - classMap for track-row, fav-icon, and cell classes; hoisted search term lookup
+- `frontend/src/components/queue-panel/queue-panel.ts` - classMap for track-item with active, selected, drop-before, drop-after states
+
+## Decisions Made
+- classMap object literal allocation per-call is acceptable since classMap internally diffs previous values and only applies DOM changes for actually changed classes — net benefit over string concatenation in Lit's update cycle
+- Hoisted searchCtrl.term outside the cols.map loop — avoids redundant property access per column per row
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- All render hot path optimizations complete for track-list and queue-panel
+- Ready for Plan 04 (final phase 8 plan)
+
+## Self-Check: PASSED
+
+All key files exist on disk. All task commits verified in git history.
+
+---
+*Phase: 08-frontend-performance-ux*
+*Completed: 2026-03-05*