docs(14-03): complete render & store optimization plan

- Created 14-03-SUMMARY.md with event delegation and store batching results - Updated STATE.md with plan progress, decisions, and session continuity - Updated ROADMAP.md with Phase 14 plan progress
2026-03-14 13:56:46 -04:00
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+---
+phase: 14-performance-optimization
+plan: 03
+subsystem: performance
+tags: [event-delegation, queueMicrotask, closure-elimination, scroll-perf, store-batching]
+
+# Dependency graph
+requires:
+  - phase: 14-01
+    provides: CSS containment and GPU scroll promotion for scroll containers
+provides:
+  - Zero per-item closure allocation during scroll rendering in track-list and queue-panel
+  - queueMicrotask notification batching in queue store
+  - changeGeneration counter in library store for granular update skipping
+affects: [14-04, ui-performance]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - Event delegation via data-index attributes replacing per-item inline closures
+    - queueMicrotask batching for store notifications (now consistent across all stores)
+    - changeGeneration counter to skip requestUpdate on loading-only state transitions
+
+key-files:
+  created: []
+  modified:
+    - frontend/src/components/track-list/track-list.ts
+    - frontend/src/components/queue-panel/queue-panel.ts
+    - frontend/src/store/queue-store.ts
+    - frontend/src/store/library-store.ts
+    - frontend/src/store/controllers/library-controller.ts
+
+key-decisions:
+  - "Event delegation via data-index + closest() instead of bound-method-per-row pattern"
+  - "changeGeneration counter in library store instead of typed per-data subscriptions"
+
+patterns-established:
+  - "Event delegation: attach handlers on virtualizer element, resolve item via closest + data-index"
+  - "Store change generation: monotonic counter for data-only changes, skip updates on loading toggles"
+
+requirements-completed: [PERF-RENDER-01, PERF-RENDER-02]
+
+# Metrics
+duration: 4min
+completed: 2026-03-14
+---
+
+# Phase 14 Plan 03: Render & Store Optimization Summary
+
+**Event delegation eliminates per-scroll-frame closure allocation; queueMicrotask batching and changeGeneration counter reduce unnecessary re-renders**
+
+## Performance
+
+- **Duration:** 4 min
+- **Started:** 2026-03-14T17:49:45Z
+- **Completed:** 2026-03-14T17:54:13Z
+- **Tasks:** 2
+- **Files modified:** 5
+
+## Accomplishments
+- Eliminated all inline arrow function closures from `renderTrackRow` (track-list) and `renderTrackItem` (queue-panel), removing GC pressure during rapid scrolling
+- Added queueMicrotask-based notification batching to queue store, matching the library store pattern
+- Added changeGeneration counter to library store so LibraryController skips requestUpdate when only loading flags toggle (no actual data change)
+- Confirmed cover-grid already uses event delegation — no changes needed
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Eliminate per-item closure allocation in render hot paths** - `2f7ed70` (perf)
+2. **Task 2: Add notification batching to queue store and granular subscriptions to library store** - `d0c05dc` (perf)
+
+## Files Created/Modified
+- `frontend/src/components/track-list/track-list.ts` - Event delegation via data-index; removed 5 inline closures per row from renderTrackRow
+- `frontend/src/components/queue-panel/queue-panel.ts` - Event delegation via data-index; removed 5 inline closures per item from renderTrackItem
+- `frontend/src/store/queue-store.ts` - queueMicrotask batching for notify()
+- `frontend/src/store/library-store.ts` - changeGeneration counter incremented on actual data changes
+- `frontend/src/store/controllers/library-controller.ts` - Checks changeGeneration before requestUpdate
+
+## Decisions Made
+- **Event delegation via data-index + closest()** — chosen over per-row bound method references because it requires zero function objects in renderItem, not just stable ones. The virtualizer and its children share the same shadow root so event.target.closest() works correctly.
+- **changeGeneration counter** — chosen over typed per-data subscriptions (subscribeTo('tracks')) because it's simpler, backward-compatible, and eliminates the biggest source of unnecessary re-renders (loading flag transitions during eagerFetch cause 8+ requestUpdate calls) without requiring store API changes for existing subscribers.
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Rule 1 - Bug] Removed unused handleRemoveTrack method**
+- **Found during:** Task 1 (queue-panel event delegation)
+- **Issue:** After delegating remove-button click to the virtualizer handler, the old `handleRemoveTrack` method became unused, causing a TypeScript error (TS6133)
+- **Fix:** Removed the unused method; remove logic is now in `onDelegatedClick` which checks `closest('.remove-button')`
+- **Files modified:** frontend/src/components/queue-panel/queue-panel.ts
+- **Verification:** Build passes, pre-commit typecheck passes
+- **Committed in:** 2f7ed70 (Task 1 commit)
+
+---
+
+**Total deviations:** 1 auto-fixed (1 bug)
+**Impact on plan:** Trivial cleanup of dead code after refactoring. No scope creep.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Plans 14-01, 14-02, 14-03 complete
+- Ready for 14-04 (remaining rendering optimizations)
+
+## Self-Check: PASSED
+
+All 5 modified files verified on disk. Both task commits (2f7ed70, d0c05dc) verified in git history.
+
+---
+*Phase: 14-performance-optimization*
+*Completed: 2026-03-14*