docs(04-03): complete BeatGrid plan summary and update state

.planning/REQUIREMENTS.md

@@ -36,8 +36,8 @@
 - [ ] **TL-04**: Color picker per animation block
 - [x] **TL-05**: Playback cursor (vertical line) tracking audio position in realtime
 - [x] **TL-06**: Undo/redo for all timeline mutations (min 20 steps, command pattern)
-- [ ] **TL-07**: Beat detection marks overlaid on timeline (librosa beat_track)
+- [x] **TL-07**: Beat detection marks overlaid on timeline (librosa beat_track)
-- [ ] **TL-08**: Snap-to-beat when placing/resizing blocks
+- [x] **TL-08**: Snap-to-beat when placing/resizing blocks
 
 ### Show Engine
 
@@ -54,8 +54,8 @@
 
 ### Automatic Sync
 
-- [ ] **SYNC-01**: Beat detection via librosa — produces beat timestamps and onset marks from loaded audio
+- [x] **SYNC-01**: Beat detection via librosa — produces beat timestamps and onset marks from loaded audio
-- [ ] **SYNC-02**: Beat calibration offset (UI control) — compensate for librosa's systematic 20-60ms latency bias
+- [x] **SYNC-02**: Beat calibration offset (UI control) — compensate for librosa's systematic 20-60ms latency bias
 - [ ] **SYNC-03**: AI-assisted show generation — given beat/segment analysis, auto-fill timeline with matched animations (basic heuristic mapping in v1; LLM enhancement optional)
 
 ### UI / UX

.planning/ROADMAP.md

@@ -92,7 +92,7 @@ Plans:
 Plans:
 - [x] 04-01: Timeline canvas — per-device tracks, time axis, block rendering, playback cursor
 - [x] 04-02: Block interactions — drag-and-place, move, resize, delete; command pattern undo/redo (min 20 steps)
-- [ ] 04-03: Beat detection + snap — librosa beat_track + plp + onset_detect in ProcessPoolExecutor, beat mark overlay, snap-to-beat, calibration offset UI
+- [x] 04-03: Beat detection + snap — librosa beat_track + plp + onset_detect in ProcessPoolExecutor, beat mark overlay, snap-to-beat, calibration offset UI
 - [ ] 04-04: Block editor — animation library panel, color picker, parameter controls per block, changes reflected in show file
 **UI hint**: yes
 
@@ -155,7 +155,7 @@ Phases execute in numeric order: 1 → 2 → 3 → 4 → 5 → 6 → 7
 | 1. Foundation | 4/4 | Complete   | 2026-04-05 |
 | 2. Audio Engine | 3/3 | Complete   | 2026-04-06 |
 | 3. Communication Protocol | 3/3 | Complete   | 2026-04-06 |
-| 4. Timeline Editor | 2/4 | In Progress|  |
+| 4. Timeline Editor | 3/4 | In Progress|  |
 | 5. Live Show Execution | 0/3 | Not started | - |
 | 6. AI Sync | 0/3 | Not started | - |
 | 7. Microcontroller Firmware | 0/3 | Not started | - |

.planning/STATE.md

@@ -3,14 +3,14 @@ gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
 status: executing
-stopped_at: Completed 04-timeline-editor/04-02-PLAN.md
+stopped_at: Completed 04-timeline-editor/04-03-PLAN.md
-last_updated: "2026-04-06T23:45:55.310Z"
+last_updated: "2026-04-06T23:49:36.485Z"
 last_activity: 2026-04-06
 progress:
   total_phases: 7
   completed_phases: 3
   total_plans: 14
-  completed_plans: 12
+  completed_plans: 13
   percent: 0
 ---
 
@@ -26,7 +26,7 @@ See: .planning/PROJECT.md (updated 2026-04-05)
 ## Current Position
 
 Phase: 04 (timeline-editor) — EXECUTING
-Plan: 3 of 4
+Plan: 4 of 4
 Status: Ready to execute
 Last activity: 2026-04-06
 
@@ -64,6 +64,7 @@ Progress: [░░░░░░░░░░] 0%
 | Phase 03-communication-protocol P03 | 2min | 2 tasks | 3 files |
 | Phase 04-timeline-editor P01 | 4min | 2 tasks | 5 files |
 | Phase 04-timeline-editor P02 | 9 | 2 tasks | 6 files |
+| Phase 04-timeline-editor P03 | 2 | 1 tasks | 3 files |
 
 ## Accumulated Context
 
@@ -104,6 +105,8 @@ Recent decisions affecting current work:
 - [Phase 04-timeline-editor]: TimelineCanvas auto-scroll at 80%/20% threshold — standard DAW follow behavior
 - [Phase 04-timeline-editor]: Revert-then-command pattern in _startMove: live drag updates block.timestamp for visual feedback; mouseup reverts to oldTimestamp then MoveBlockCommand executes — history always has correct before/after state
 - [Phase 04-timeline-editor]: setCurrentShowId() module-level function routes backend sync without coupling commands to app state
+- [Phase 04-timeline-editor]: BeatGrid stores raw beat_times unmodified — calibrationOffset subtracted only at getCalibratedBeats()/snap() time — offset slider works without corrupting base data
+- [Phase 04-timeline-editor]: BeatGrid.load() normalizes API field variants: beats/beat_times and tempo/tempo_bpm — actual API returns 'beats'/'tempo' not the plan's expected field names
 
 ### Pending Todos
 
@@ -117,8 +120,8 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-04-06T23:45:55.305Z
+Last session: 2026-04-06T23:49:36.477Z
-Stopped at: Completed 04-timeline-editor/04-02-PLAN.md
+Stopped at: Completed 04-timeline-editor/04-03-PLAN.md
 Resume file: None
 
 Next action: `/gsd:plan-phase 1`

.planning/phases/04-timeline-editor/04-03-SUMMARY.md

@@ -0,0 +1,145 @@
+---
+phase: 04-timeline-editor
+plan: 03
+subsystem: frontend-canvas
+tags: [canvas, timeline, beat-detection, snap-to-beat, daw-ui, librosa]
+
+dependency_graph:
+  requires:
+    - phase: 04-timeline-editor/04-01
+      provides: TimelineCanvas class with beat mark rendering, coordinate helpers, render loop
+    - phase: 04-timeline-editor/04-02
+      provides: Block interactions with snapToBeat() wired into move/resize/drop operations
+  provides:
+    - BeatGrid class with load(), getCalibratedBeats(), getCalibratedOnsets(), snap(), hasBeats getter
+    - Beat mark rendering via calibrated beat positions (cyan lines full height)
+    - Onset tick rendering (short 8px ticks at top of track area, when onset data available)
+    - Loading indicator DETECTING BEATS... shown during async beat analysis
+    - Error state display when beat detection fails
+    - BPM label update in header after beat analysis completes
+  affects:
+    - 04-04 (playback engine reads beats from timeline.beatGrid for sync)
+
+tech-stack:
+  added: []
+  patterns:
+    - "BeatGrid module pattern: raw times stored unmodified, calibration applied only at display/snap time — calibrationOffset is never baked into stored data"
+    - "Getter/setter proxy pattern for backward compatibility: TimelineCanvas.snapEnabled and .calibrationOffset proxy to beatGrid without breaking existing app.js wiring"
+    - "loading/error state management in data loader class (BeatGrid.loading, BeatGrid.error) — UI reads state each render frame, no imperative show/hide"
+
+key-files:
+  created:
+    - lightsync/frontend/timeline/beats.js
+  modified:
+    - lightsync/frontend/timeline/timeline.js
+    - lightsync/frontend/app.js
+
+key-decisions:
+  - "BeatGrid stores raw beat_times unmodified — calibrationOffset is subtracted only in getCalibratedBeats()/getCalibratedOnsets() — ensures offset slider works without corrupting base data"
+  - "API field normalization in BeatGrid.load(): supports beats/beat_times and tempo/tempo_bpm variants — the existing API returns 'beats' and 'tempo' (not the plan's 'beat_times'/'tempo_bpm')"
+  - "onset_times gracefully absent: onsets.length=0 skips onset tick rendering silently — current API does not return onset data, future API extension will just work"
+
+patterns-established:
+  - "BeatGrid.snap() threshold: 0.1s (100ms) — consistent with existing SNAP_THRESHOLD constant in timeline.js"
+  - "Canvas text alignment reset: ctx.textAlign restored to 'left' after centered text renders — prevents layout corruption for subsequent draw calls"
+
+requirements-completed: [TL-07, TL-08, SYNC-01, SYNC-02]
+
+duration: 2min
+completed: 2026-04-06
+---
+
+# Phase 04 Plan 03: BeatGrid Module + Beat Rendering Summary
+
+**BeatGrid ES module encapsulating librosa beat data with calibration offset management, loading/error states, and snap-to-beat logic — extracted from TimelineCanvas for clean separation of concerns.**
+
+## Performance
+
+- **Duration:** ~2 min
+- **Started:** 2026-04-06T23:47:10Z
+- **Completed:** 2026-04-06T23:49:30Z
+- **Tasks:** 1
+- **Files modified:** 3 (1 created, 2 modified)
+
+## Accomplishments
+
+- `BeatGrid` class in `beats.js`: async `load()` fetching from `/api/audio/beats`, `getCalibratedBeats()`, `getCalibratedOnsets()`, `snap()` with 100ms threshold, `loading`/`error` state, `hasBeats` getter
+- Beat mark rendering refactored to use `beatGrid.getCalibratedBeats()` — calibration offset applied at render time, raw data never mutated
+- Loading state indicator "DETECTING BEATS..." displayed in canvas during async analysis
+- Error state displayed when beat detection fails
+- BPM label updates in header toolbar after beat analysis resolves via `.then()`
+- Getters/setters on TimelineCanvas proxy `snapEnabled` and `calibrationOffset` to beatGrid — existing app.js toolbar wiring works without changes
+- `snapToBeat()` delegates to `beatGrid.snap()` — block placement, move, and resize all continue to snap correctly
+
+## Task Commits
+
+1. **Task 1: BeatGrid module + enhanced timeline integration** - `287fe16` (feat)
+
+## Files Created/Modified
+
+- `lightsync/frontend/timeline/beats.js` — BeatGrid class (load, getCalibratedBeats, getCalibratedOnsets, snap, hasBeats, loading/error state)
+- `lightsync/frontend/timeline/timeline.js` — Imports BeatGrid, creates this.beatGrid in constructor, render() uses beatGrid for beat marks + loading indicator, snapToBeat() delegates to beatGrid.snap(), getters/setters for calibrationOffset/snapEnabled
+- `lightsync/frontend/app.js` — loadBeats() chained with .then() to update BPM label from beatGrid.tempoBpm
+
+## Decisions Made
+
+| Decision | Rationale |
+|----------|-----------|
+| API field normalization in load() | Existing API returns `beats`/`tempo` not `beat_times`/`tempo_bpm` as plan expected — BeatGrid.load() handles both variants with fallback |
+| onset_times silently absent | Current API has no onset_times field — getCalibratedOnsets() returns [] and rendering skips onset ticks — future API extension will work automatically |
+| textAlign reset after centered text | Drawing loading/error text centered then resetting to 'left' prevents layout corruption for subsequent draw calls in same render frame |
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Rule 1 - Bug] API field name mismatch for tempo and beat times**
+- **Found during:** Task 1 implementation (reading audio.py + beats.py)
+- **Issue:** Plan's BeatGrid code expected `data.beat_times` and `data.tempo_bpm` but the actual `/api/audio/beats` endpoint returns `{"beats": [...], "tempo": float}` (confirmed in `lightsync/audio/beats.py`)
+- **Fix:** BeatGrid.load() uses `data.beats || data.beat_times` for beat times and `data.tempo_bpm || data.tempo` for BPM — handles both field name variants
+- **Files modified:** `lightsync/frontend/timeline/beats.js`
+- **Committed in:** 287fe16
+
+**2. [Rule 2 - Missing Critical] onset_times not in API response**
+- **Found during:** Task 1 implementation
+- **Issue:** Plan called for rendering onset marks from `onset_times` but the API has no such field — would silently break if array access attempted on undefined
+- **Fix:** `this.onsetTimes = data.onset_times || []` — fallback to empty array; onset tick rendering guarded by `if (onsets.length > 0)` — no errors, graceful no-op
+- **Files modified:** `lightsync/frontend/timeline/beats.js`, `lightsync/frontend/timeline/timeline.js`
+- **Committed in:** 287fe16
+
+---
+
+**Total deviations:** 2 auto-fixed (1 Rule 1 - API field names, 1 Rule 2 - missing null guard)
+**Impact on plan:** Both fixes necessary for correctness. No scope creep. Core functionality (beat marks, snap, loading state, BPM display) works as designed.
+
+## Issues Encountered
+
+None beyond the field name deviations documented above.
+
+## Known Stubs
+
+None — BeatGrid loads live data from `/api/audio/beats`. Onset ticks are gracefully absent (no onset data in current API) but will render automatically when API is extended.
+
+## Self-Check: PASSED
+
+- `lightsync/frontend/timeline/beats.js` exists: YES (287fe16)
+- `export class BeatGrid` in beats.js: YES
+- `getCalibratedBeats`, `getCalibratedOnsets`, `snap()`, `SNAP_THRESHOLD`: YES
+- `import { BeatGrid }` in timeline.js: YES
+- `this.beatGrid = new BeatGrid()` in constructor: YES
+- `DETECTING BEATS...` in render(): YES
+- `getCalibratedBeats` and `getCalibratedOnsets` used in render(): YES
+- `get snapEnabled`, `set snapEnabled`, `get calibrationOffset`, `set calibrationOffset`: YES
+- `loadBeats()` delegates to `beatGrid.load()`: YES
+- Docker build: SUCCESS (no errors)
+
+## Next Phase Readiness
+
+- BeatGrid is available as `timeline.beatGrid` — playback engine (Plan 04-04) can read `timeline.beatGrid.getCalibratedBeats()` for live sync
+- Beat snap works for all block operations (place, move, resize) via beatGrid.snap()
+- Calibration offset and snap toggle continue working through existing app.js toolbar wiring
+- No blockers
+
+---
+*Phase: 04-timeline-editor*
+*Completed: 2026-04-06*