docs(14-01): complete CSS containment & GPU scroll promotion plan

- SUMMARY.md with 2 tasks, 7 files, 3 min duration - STATE.md updated with plan position, metrics, decisions - ROADMAP.md updated with plan progress (2/4)
2026-03-14 13:48:36 -04:00
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+---
+phase: 14-performance-optimization
+plan: 01
+subsystem: ui
+tags: [css-containment, gpu-compositing, will-change, content-visibility, scroll-performance]
+
+# Dependency graph
+requires: []
+provides:
+  - CSS containment on all app shell layout boundaries
+  - GPU-composited scrolling on all 6 scroll-heavy components
+  - content-visibility auto on album cards for off-screen rendering skip
+affects: [14-performance-optimization]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: [CSS contain for layout isolation, will-change transform for GPU scroll promotion, content-visibility auto for off-screen rendering skip]
+
+key-files:
+  created: []
+  modified:
+    - frontend/index.css
+    - frontend/src/components/cover-grid/cover-grid-styles.ts
+    - frontend/src/components/track-list/track-list.ts
+    - frontend/src/components/queue-panel/queue-panel.ts
+    - frontend/src/components/artists-view/artists-view.ts
+    - frontend/src/components/genres-view/genres-view.ts
+    - frontend/src/components/playlist-view/playlist-view.ts
+
+key-decisions:
+  - "contain: strict on .main-panel (has explicit dimensions), layout style elsewhere (avoids breaking flex)"
+  - "will-change: transform only on scroll containers (not :host) to avoid wasting GPU memory"
+  - "content-visibility: auto on album cards with contain-intrinsic-size hint to prevent layout shift"
+
+patterns-established:
+  - "CSS containment pattern: :host gets contain: layout style; scroll container gets contain: paint + will-change: transform"
+  - "content-visibility: auto with contain-intrinsic-size for cards in virtualized grids"
+
+requirements-completed: [PERF-SCROLL-01, PERF-SCROLL-02]
+
+# Metrics
+duration: 3min
+completed: 2026-03-14
+---
+
+# Phase 14 Plan 01: CSS Containment & GPU Scroll Promotion Summary
+
+**CSS containment on app shell boundaries + GPU-composited scrolling on all 6 scroll-heavy components with content-visibility on album cards**
+
+## Performance
+
+- **Duration:** 3 min
+- **Started:** 2026-03-14T17:43:01Z
+- **Completed:** 2026-03-14T17:46:24Z
+- **Tasks:** 2
+- **Files modified:** 7
+
+## Accomplishments
+- App shell layout boundaries (content-area, main-panel, sidebar, bottom-bar) isolated with CSS containment to prevent cross-boundary layout recalculation
+- All 6 scroll-heavy components (cover-grid, track-list, queue-panel, artists-view, genres-view, playlist-view) now have CSS containment on :host and GPU layer promotion on scroll containers
+- Album cards skip rendering when off-screen via content-visibility: auto with intrinsic size hints
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Add CSS containment to app shell layout boundaries** - `efa06f7` (perf)
+2. **Task 2: Add GPU promotion and containment to all scroll containers** - `ac8a52e` (perf)
+
+## Files Created/Modified
+- `frontend/index.css` - CSS containment on .content-area, .main-panel, .main-panel > *, sidebar, .bottom-bar
+- `frontend/src/components/cover-grid/cover-grid-styles.ts` - contain + will-change on scroll container, content-visibility on album cards
+- `frontend/src/components/track-list/track-list.ts` - contain on :host, contain + will-change on lit-virtualizer
+- `frontend/src/components/queue-panel/queue-panel.ts` - contain on :host, contain + will-change on lit-virtualizer
+- `frontend/src/components/artists-view/artists-view.ts` - contain on :host, contain + will-change on grid scroll container
+- `frontend/src/components/genres-view/genres-view.ts` - contain on :host, contain + will-change on grid scroll container
+- `frontend/src/components/playlist-view/playlist-view.ts` - contain on :host, contain + will-change on playlist-list
+
+## Decisions Made
+- Used `contain: strict` only on `.main-panel` (has explicit flex: 1 + overflow: hidden), used `contain: layout style` elsewhere to avoid breaking flex layouts
+- Applied `will-change: transform` only to actual scroll containers (not :host elements) to avoid wasting GPU memory on non-scrolling elements
+- Added `content-visibility: auto` with `contain-intrinsic-size` hints on album cards to prevent layout shift during scroll
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- CSS containment foundation in place for all components
+- Ready for Plan 02 (next performance optimization plan in phase 14)
+
+---
+*Phase: 14-performance-optimization*
+*Completed: 2026-03-14*
+
+## Self-Check: PASSED