docs(06-02): complete audio feature extraction and segment overlay plan

- Create 06-02-SUMMARY.md with full execution record
- Update STATE.md: plan advanced to 3/3, progress 95%, decisions logged
- Update ROADMAP.md: phase 6 now 2/3 summaries
- Mark SYNC-03 complete in REQUIREMENTS.md

.planning/REQUIREMENTS.md

@@ -56,7 +56,7 @@
 
 - [x] **SYNC-01**: Beat detection via librosa — produces beat timestamps and onset marks from loaded audio
 - [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)
+- [x] **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
 
@@ -121,7 +121,7 @@
 | TL-07, TL-08, SYNC-01, SYNC-02 | Phase 4 | Pending |
 | SHW-03, UI-03 | Phase 5 | Pending |
 | UI-01, UI-02, UI-04 | Phases 1-5 (progressive) | Pending |
-| SYNC-03 | Phase 6 | Pending |
+| SYNC-03 | Phase 6 | Complete |
 | FW-01, FW-02 | Phase 7 | Pending |
 
 **Coverage:**

.planning/ROADMAP.md

@@ -127,7 +127,7 @@ Plans:
 
 Plans:
 - [x] 06-01: YouTube loading — yt-dlp download to /app/shows/, SSE progress streaming, transport bar URL input
-- [ ] 06-02: Feature extraction + segmentation — onset/chroma/RMS extraction, structural segmentation API, colored section band overlay on waveform
+- [x] 06-02: Feature extraction + segmentation — onset/chroma/RMS extraction, structural segmentation API, colored section band overlay on waveform
 - [ ] 06-03: AI sync engine — heuristic block mapper + optional LLM generation, AI Sync panel UI, per-section fill
 
 ### Phase 7: Microcontroller Firmware
@@ -158,5 +158,5 @@ Phases execute in numeric order: 1 → 2 → 3 → 4 → 5 → 6 → 7
 | 3. Communication Protocol | 3/3 | Complete   | 2026-04-06 |
 | 4. Timeline Editor | 4/4 | Complete   | 2026-04-06 |
 | 5. Live Show Execution | 4/4 | Complete   | 2026-04-07 |
-| 6. AI Sync | 1/3 | In Progress|  |
+| 6. AI Sync | 2/3 | In Progress|  |
 | 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 06-ai-sync/06-01-PLAN.md
+stopped_at: Completed 06-ai-sync/06-02-PLAN.md
-last_updated: "2026-04-07T11:38:05.324Z"
+last_updated: "2026-04-07T11:42:33.193Z"
 last_activity: 2026-04-07
 progress:
   total_phases: 7
   completed_phases: 5
   total_plans: 21
-  completed_plans: 19
+  completed_plans: 20
   percent: 0
 ---
 
@@ -26,7 +26,7 @@ See: .planning/PROJECT.md (updated 2026-04-05)
 ## Current Position
 
 Phase: 06 (ai-sync) — EXECUTING
-Plan: 2 of 3
+Plan: 3 of 3
 Status: Ready to execute
 Last activity: 2026-04-07
 
@@ -71,6 +71,7 @@ Progress: [░░░░░░░░░░] 0%
 | Phase 05-live-show-execution P03 | 10 | 1 tasks | 1 files |
 | Phase 05-live-show-execution P04 | 1 | 1 tasks | 1 files |
 | Phase 06-ai-sync P01 | 8 | 3 tasks | 6 files |
+| Phase 06-ai-sync P02 | 8 | 2 tasks | 7 files |
 
 ## Accumulated Context
 
@@ -125,6 +126,8 @@ Recent decisions affecting current work:
 - [Phase 05-live-show-execution]: Audio element event listeners are correct hook for mouse play/pause WS messages — fire for all triggers (button/keyboard/programmatic), idempotent with wireKeyboard() sends
 - [Phase 06-ai-sync]: sys.executable -m yt_dlp used to avoid PATH issues in Docker container
 - [Phase 06]: yt-dlp --newline flag required for line-by-line progress parsing
+- [Phase 06-ai-sync]: Segment band drawing inserted between row banding and waveform in render() for correct Z-order
+- [Phase 06-ai-sync]: Auto segment count: max(4, min(12, int(duration / 30))) for typical songs
 
 ### Pending Todos
 
@@ -138,8 +141,8 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-04-07T11:37:58.939Z
+Last session: 2026-04-07T11:42:33.186Z
-Stopped at: Completed 06-ai-sync/06-01-PLAN.md
+Stopped at: Completed 06-ai-sync/06-02-PLAN.md
 Resume file: None
 
 Next action: `/gsd:plan-phase 1`

.planning/phases/06-ai-sync/06-02-SUMMARY.md

@@ -0,0 +1,102 @@
+---
+phase: 06-ai-sync
+plan: 02
+subsystem: audio-analysis
+tags: [librosa, segmentation, feature-extraction, canvas-overlay, timeline]
+dependency_graph:
+  requires: [06-01]
+  provides: [audio-features, structural-segments, segment-overlay-ui]
+  affects: [lightsync/audio, lightsync/api/audio.py, lightsync/frontend/timeline]
+tech_stack:
+  added: []
+  patterns: [asyncio.to_thread for CPU-bound librosa analysis, canvas overlay layer, agglomerative clustering]
+key_files:
+  created:
+    - lightsync/audio/features.py
+    - lightsync/audio/segments.py
+    - lightsync/frontend/timeline/segments.js
+  modified:
+    - lightsync/api/audio.py
+    - lightsync/main.py
+    - lightsync/frontend/timeline/timeline.js
+    - lightsync/frontend/app.js
+decisions:
+  - "Segment band drawing inserted between step 2 (track row banding) and step 3 (waveform) in render() for correct Z-order"
+  - "agglomerative returns k boundaries yielding k+1 sections — all_times = [0.0] + bound_times + [duration] pattern"
+  - "Auto segment count heuristic: max(4, min(12, int(duration / 30))) — 4-12 sections for typical songs"
+  - "Segment click handling added on empty-canvas clicks only — block interactions take priority"
+  - "BAND_COLORS alternates 3 colors (cyan, purple, darker-cyan) for visual variety"
+metrics:
+  duration: "~8 min"
+  completed: "2026-04-07"
+  tasks_completed: 2
+  files_changed: 7
+requirements_satisfied: [SYNC-03]
+---
+
+# Phase 06 Plan 02: Audio Feature Extraction and Segment Overlay Summary
+
+**One-liner:** Librosa-based audio feature extraction (onsets, chroma, RMS) and structural segmentation with interactive translucent section bands on the timeline canvas.
+
+## What Was Built
+
+Added structural audio analysis foundation for the AI sync engine and visible segment overlay UI:
+
+1. **Feature extraction backend (Task 1, partial):** New `lightsync/audio/features.py` module:
+   - `extract_features(path)` extracts onset_times, rms_1s, chroma_1s, duration, sr
+   - Uses librosa onset detection, chroma_cqt, and RMS energy; reduces to 1s resolution
+   - `extract_features_async` wraps in asyncio.to_thread
+
+2. **Segmentation backend (Task 1, partial):** New `lightsync/audio/segments.py` module:
+   - `detect_segments(path, n_segments=None)` uses chroma + recurrence matrix + agglomerative clustering
+   - Auto segment count heuristic: `max(4, min(12, int(duration / 30)))` for 4-12 sections
+   - Returns `[{"start": float, "end": float, "label": "SEC N"}, ...]`
+   - `detect_segments_async` wraps in asyncio.to_thread
+
+3. **API endpoints (Task 1, partial):**
+   - `GET /api/audio/segments?path=...` — returns cached structural segments
+   - `GET /api/audio/features?path=...` — returns onsets, chroma, RMS
+   - Both endpoints added to `lightsync/api/audio.py`
+   - `app.state.segments = {}` cache initialized in `main.py` lifespan
+
+4. **Segment overlay UI (Task 2):** New `lightsync/frontend/timeline/segments.js`:
+   - `SegmentOverlay` class manages segment data, drawing, and click interaction
+   - `draw()` renders translucent colored bands using BAND_COLORS (cyan/purple alternation)
+   - `handleClick(time)` selects segment containing that time, deselects on empty click
+   - `getSelected()` returns currently selected segment or null
+   - Labels render as `SEC 1`, `SEC 2`, etc. in 9px monospace at top-left of each band
+   - Selected band highlighted with 1px `rgba(0,255,255,1.0)` border
+
+5. **Timeline integration (Task 2):**
+   - `import { SegmentOverlay }` added to `timeline.js`
+   - `this.segmentOverlay = new SegmentOverlay()` in constructor
+   - `segmentOverlay.draw()` inserted between step 2 (row banding) and step 3 (waveform) in render()
+   - `async loadSegments(audioPath)` method added to TimelineCanvas
+   - Segment click handling in mousedown: empty-canvas clicks update segment selection
+   - `timeline.loadSegments(path)` called in `app.js` loadedmetadata handler
+
+## Commits
+
+| Task | Commit | Description |
+|------|--------|-------------|
+| 1 | `d339ba5` | feat(06-02): add feature extraction and segmentation backend modules + API |
+| 2 | `48e15ee` | feat(06-02): add segment overlay canvas rendering and click interaction |
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Known Stubs
+
+None - all functionality is fully wired.
+
+## Self-Check: PASSED
+
+- `lightsync/audio/features.py` exists: contains `def extract_features`, `async def extract_features_async`, `librosa.onset.onset_detect`, `librosa.feature.chroma_cqt`, `librosa.feature.rms`, returns keys `onset_times`, `rms_1s`, `chroma_1s`, `duration`, `sr`
+- `lightsync/audio/segments.py` exists: contains `def detect_segments`, `async def detect_segments_async`, `librosa.segment.agglomerative`, `librosa.segment.recurrence_matrix`, `SEC {i + 1}`, `max(4, min(12,`
+- `lightsync/api/audio.py` contains `async def get_segments`, `async def get_features`, `from lightsync.audio.segments import detect_segments_async`, `from lightsync.audio.features import extract_features_async`
+- `lightsync/main.py` contains `app.state.segments = {}`
+- `lightsync/frontend/timeline/segments.js` exists: contains `class SegmentOverlay`, `export { SegmentOverlay }`, `BAND_COLORS`, `rgba(0,255,255,0.15)`, `rgba(180,0,255,0.15)`, `handleClick`, `getSelected`, `seg.label`, `9px monospace`
+- `lightsync/frontend/timeline/timeline.js` contains `import { SegmentOverlay }`, `this.segmentOverlay = new SegmentOverlay()`, `segmentOverlay.draw(`, `async loadSegments(audioPath)`
+- `lightsync/frontend/app.js` contains `loadSegments(path)` in loadedmetadata handler
+- All task commits exist: `d339ba5`, `48e15ee`