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)

.planning/ROADMAP.md

@@ -120,7 +120,7 @@ Plans:
   3. Render hot paths (renderTrackRow, renderTrackItem) create zero new closures per frame — all event handling uses delegation
   4. Store notifications are batched (queueMicrotask) and components only re-render when their relevant data changes
   5. A profiling guide documents how to diagnose performance issues using pprof (backend) and DevTools (frontend)
-**Plans:** 1/4 plans executed
+**Plans:** 2/4 plans executed
 Plans:
 - [ ] 14-01-PLAN.md — CSS containment + GPU layer promotion on all scroll containers
 - [ ] 14-02-PLAN.md — View caching navigation system (replace innerHTML destruction)
@@ -144,7 +144,7 @@ Plans:
 | 11. Per-Library Scan Pipeline | 3/3 | Complete    | 2026-03-09 | - |
 | 12. Library CRUD & Data Integrity | v1.1 | 1/2 | In Progress | - |
 | 13. Library Views & Phantom Tracks | v1.1 | 0/? | Not started | - |
-| 14. Performance Optimization | 1/4 | In Progress|  | - |
+| 14. Performance Optimization | 2/4 | In Progress|  | - |
 
 ---
 *Roadmap created: 2026-02-27*

.planning/STATE.md

@@ -23,10 +23,10 @@ See: .planning/PROJECT.md (updated 2026-03-08)
 ## Current Position
 
 Phase: 14 — Performance Optimization
-Plan: 1 of 4 in Phase (Plan 02 complete)
+Plan: 2 of 4 in Phase (Plans 01, 02 complete)
-Status: Plan 14-02 complete — view caching navigation system
+Status: Plan 14-01 complete — CSS containment & GPU scroll promotion
-Progress: ████████████████░░░░ Phase 14 in progress (1/4 plans)
+Progress: ████████████████░░░░ Phase 14 in progress (2/4 plans)
-Last activity: 2026-03-14 — Completed 14-02 view caching navigation
+Last activity: 2026-03-14 — Completed 14-01 CSS containment & GPU scroll promotion
 
 ### Phase Overview
 
@@ -37,7 +37,7 @@ Last activity: 2026-03-14 — Completed 14-02 view caching navigation
 | 11. Per-Library Scan Pipeline | Complete (3/3 plans) ✅ |
 | 12. Library CRUD & Data Integrity | In progress (1/2 plans) |
 | 13. Library Views & Phantom Tracks | Not started |
-| 14. Performance Optimization | In progress (1/4 plans) |
+| 14. Performance Optimization | In progress (2/4 plans) |
 
 ## Performance Metrics
 
@@ -58,6 +58,7 @@ Last activity: 2026-03-14 — Completed 14-02 view caching navigation
 | Phase 11-02 P02 | 4 min | 2 tasks | 2 files |
 | Phase 12-01 P01 | 6 min | 2 tasks | 6 files |
 | Phase 14-02 P02 | 1 min | 1 task | 1 file |
+| Phase 14-01 P01 | 3 min | 2 tasks | 7 files |
 
 ## Accumulated Context
 
@@ -128,6 +129,9 @@ Decisions from v1.0 are archived in PROJECT.md Key Decisions table. Key patterns
 | Primary views cached, detail views ephemeral | Detail views depend on entity IDs that change; caching would show stale content |
 | Inline style.display toggle over CSS class | Simpler, no specificity issues, empty string restores natural display value |
 | viewCache bounded at 6 entries | One per primary view — negligible memory since data is already in store caches |
+| contain: strict only on .main-panel | Has explicit dimensions (flex: 1, overflow: hidden); elsewhere use layout style to not break flex |
+| will-change: transform only on scroll containers | Not on :host — avoids wasting GPU memory on non-scrolling elements |
+| content-visibility: auto on album cards with contain-intrinsic-size | Prevents layout shift during scroll while skipping off-screen rendering |
 
 ### Warnings (carry forward)
 
@@ -155,9 +159,9 @@ Decisions from v1.0 are archived in PROJECT.md Key Decisions table. Key patterns
 ### Last Session
 
 **Date:** 2026-03-14
-**What happened:** Executed Phase 14, Plan 02 — replaced innerHTML navigation with view caching system. Primary views (tracks, albums, artists, genres, playlists, settings) are now created once and kept in DOM with display toggle instead of destruction/recreation.
+**What happened:** Executed Phase 14, Plan 01 — added CSS containment to app shell layout boundaries and GPU-composited scrolling to all 6 scroll-heavy components with content-visibility on album cards.
-**Where we stopped:** Completed 14-02-PLAN.md — Plan 02 of Phase 14 complete
+**Where we stopped:** Completed 14-01-PLAN.md — Plan 01 of Phase 14 complete (Plans 01, 02 done)
-**Next action:** Execute remaining Phase 14 plans (14-01 CSS containment, 14-03 store optimizations, 14-04 rendering optimizations)
+**Next action:** Execute remaining Phase 14 plans (14-03 store optimizations, 14-04 rendering optimizations)
 
 ---
 *State initialized: 2026-02-27*
@@ -170,4 +174,4 @@ Decisions from v1.0 are archived in PROJECT.md Key Decisions table. Key patterns
 | 18 | add multi-column metadata display to playlist-details | 2026-03-08 | ce23177 | [18-add-multi-column-metadata-display-to-pla](./quick/18-add-multi-column-metadata-display-to-pla/) |
 
 Last activity: 2026-03-08 - Completed quick task 18: add multi-column metadata display to playlist-details
-*Last updated: 2026-03-14 — Completed 14-02-PLAN.md (Phase 14 Plan 02 complete)*
+*Last updated: 2026-03-14 — Completed 14-01-PLAN.md (Phase 14 Plan 01 complete)*

.planning/phases/14-performance-optimization/14-01-SUMMARY.md

@@ -0,0 +1,103 @@
+---
+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