docs(04-01): complete timeline canvas foundation plan — SUMMARY, STATE, ROADMAP updated

- SUMMARY: timeline canvas with per-device tracks, waveform, beat marks, playback cursor
- STATE: plan advanced to 2/4, progress 79%, decisions and metrics recorded
- ROADMAP: Phase 4 progress updated (1/4 plans complete, In Progress)
- Requirements TL-01, TL-05 marked complete

.planning/STATE.md

@@ -2,15 +2,15 @@
 gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
-status: verifying
-stopped_at: Phase 4 UI-SPEC approved
-last_updated: "2026-04-06T23:11:05.583Z"
+status: executing
+stopped_at: Completed 04-timeline-editor/04-01-PLAN.md
+last_updated: "2026-04-06T23:35:19.480Z"
 last_activity: 2026-04-06
 progress:
   total_phases: 7
   completed_phases: 3
-  total_plans: 10
-  completed_plans: 10
+  total_plans: 14
+  completed_plans: 11
   percent: 0
 ---
 
@@ -21,13 +21,13 @@ progress:
 See: .planning/PROJECT.md (updated 2026-04-05)
 
 **Core value:** Load a song, build a synchronized light show, play it back live — with precise control over every effect on every device.
-**Current focus:** Phase 03 — communication-protocol
+**Current focus:** Phase 04 — timeline-editor
 
 ## Current Position
 
-Phase: 4
-Plan: Not started
-Status: Phase complete — ready for verification
+Phase: 04 (timeline-editor) — EXECUTING
+Plan: 2 of 4
+Status: Ready to execute
 Last activity: 2026-04-06
 
 Progress: [░░░░░░░░░░] 0%
@@ -62,6 +62,7 @@ Progress: [░░░░░░░░░░] 0%
 | Phase 03-communication-protocol P01 | 4min | 2 tasks | 8 files |
 | Phase 03-communication-protocol P02 | 3min | 1 tasks | 10 files |
 | Phase 03-communication-protocol P03 | 2min | 2 tasks | 3 files |
+| Phase 04-timeline-editor P01 | 4min | 2 tasks | 5 files |
 
 ## Accumulated Context
 
@@ -98,6 +99,8 @@ Recent decisions affecting current work:
 - [Phase 03-communication-protocol]: FireAnimation lazy-initializes heat array per led_count to support variable strip lengths
 - [Phase 03-communication-protocol]: asyncio.run() test pattern chosen over pytest-asyncio — not installed, plan provided this fallback
 - [Phase 03-communication-protocol]: UDPSender stopped before registry.save() in shutdown — orderly teardown, no sends after socket close
+- [Phase 04-timeline-editor]: Beats API uses 'beats' field not 'beat_times' — loadBeats() handles both with fallback
+- [Phase 04-timeline-editor]: TimelineCanvas auto-scroll at 80%/20% threshold — standard DAW follow behavior
 
 ### Pending Todos
 
@@ -111,8 +114,8 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-04-06T23:11:05.576Z
-Stopped at: Phase 4 UI-SPEC approved
-Resume file: .planning/phases/04-timeline-editor/04-UI-SPEC.md
+Last session: 2026-04-06T23:35:19.475Z
+Stopped at: Completed 04-timeline-editor/04-01-PLAN.md
+Resume file: None
 
 Next action: `/gsd:plan-phase 1`