docs(14-04): complete scroll optimization & profiling guide plan

- SUMMARY.md with task commits, decisions, and metrics - STATE.md updated with plan progress and session continuity - ROADMAP.md updated with Phase 14 plan progress
2026-03-14 13:54:36 -04:00
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+---
+phase: 14-performance-optimization
+plan: 04
+subsystem: frontend
+tags: [scroll, requestAnimationFrame, profiling, pprof, devtools, performance]
+
+# Dependency graph
+requires:
+  - phase: 14-performance-optimization
+    provides: CSS containment and GPU scroll layer promotion (Plan 01), view caching navigation (Plan 02)
+provides:
+  - RAF-throttled scroll position saving for cover grid
+  - overflow-anchor CSS on queue panel virtualizer
+  - Performance profiling guide (docs/PROFILING.md)
+affects: [cover-grid, queue-panel, developer-documentation]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: [RAF-throttled scroll saves instead of debounce, overflow-anchor for virtualizer scroll containers]
+
+key-files:
+  created:
+    - docs/PROFILING.md
+  modified:
+    - frontend/src/components/cover-grid/scroll-manager.ts
+    - frontend/src/components/queue-panel/queue-panel.ts
+
+key-decisions:
+  - "Keep monkey-patch alongside overflow-anchor: CSS overflow-anchor disables browser scroll anchoring but not lit-virtualizer's internal _correctScrollError, so the monkey-patch is still needed for scrollbar drag on large lists"
+  - "RAF throttle over debounce for scroll saves: saves position once per frame during scrolling instead of only after scrolling stops, preventing lost positions on quick navigation"
+
+patterns-established:
+  - "RAF-throttled scroll position saving: use requestAnimationFrame guard pattern instead of setTimeout debounce for continuous scroll position tracking"
+
+requirements-completed: [PERF-SCROLL-03, PERF-DIAG-01]
+
+# Metrics
+duration: 2min
+completed: 2026-03-14
+---
+
+# Phase 14 Plan 04: Scroll Optimization & Profiling Guide Summary
+
+**RAF-throttled scroll position saves for cover grid, overflow-anchor on queue panel virtualizer, and comprehensive performance profiling guide**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-03-14T17:49:56Z
+- **Completed:** 2026-03-14T17:52:54Z
+- **Tasks:** 2 completed, 1 pending checkpoint
+- **Files modified:** 3
+
+## Accomplishments
+- Cover grid scroll position saves are now RAF-throttled (once per ~16ms frame) instead of 100ms debounced, capturing position during continuous scrolling
+- Queue panel lit-virtualizer has `overflow-anchor: none` CSS; monkey-patch retained with expanded documentation explaining why CSS alone is insufficient
+- Comprehensive profiling guide created covering pprof backend profiling, Chrome DevTools frontend profiling, and specific diagnostic workflows
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Optimize scroll event handling and clean up queue panel scroll hack** - `6ca0b3c` (perf)
+2. **Task 2: Create performance profiling guide** - `1ec8f82` (docs)
+3. **Task 3: Verify performance improvements** - *pending checkpoint:human-verify*
+
+## Files Created/Modified
+- `frontend/src/components/cover-grid/scroll-manager.ts` - Replaced debounced scroll save with RAF-throttled save
+- `frontend/src/components/queue-panel/queue-panel.ts` - Added overflow-anchor: none CSS, expanded monkey-patch comments
+- `docs/PROFILING.md` - Performance profiling guide with backend, frontend, and workflow sections
+
+## Decisions Made
+- **Keep monkey-patch alongside overflow-anchor:** CSS `overflow-anchor: none` disables browser-native scroll anchoring but does not affect lit-virtualizer's internal `_correctScrollError()` method. The monkey-patch is still needed to suppress that internal correction during native scrollbar drag on large lists (20k+ items).
+- **RAF throttle over debounce:** requestAnimationFrame guard pattern fires once per frame (~16ms at 60fps) during active scrolling, unlike debounce which only fires after scrolling stops. This prevents lost positions if the user navigates away during scrolling.
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Task 3 (human-verify checkpoint) pending: user verification of scroll smoothness, navigation speed, and profiling guide
+- After checkpoint approval, Phase 14 is complete and ready for transition
+
+---
+*Phase: 14-performance-optimization*
+*Completed: 2026-03-14*