milestone(timeline-editor): Task #57 Phase 1 Complete - Production-Ready EditorHEADmain

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🎉 MILESTONE: Interactive Timeline Editor - Phase 1 Complete 🎉
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Task #57 Phase 1 delivers a fully functional web-based timeline editor
for demo.seq files, eliminating manual text editing and enabling visual
sequence placement with audio waveform reference.

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IMPLEMENTED FEATURES (Phase 1.1)
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Core Editing:
  ✅ Load/save demo.seq files with BPM, beat notation, priority modifiers
  ✅ Gantt-style visual timeline with dynamic sequence/effect positioning
  ✅ Drag & drop sequences and effects along timeline
  ✅ Resize effects with left/right handles (allow negative relative times)
  ✅ Snap-to-beat mode with checkbox toggle and beat markers
  ✅ Delete sequences/effects, add new sequences
  ✅ Re-order sequences by start time

Properties & Priority:
  ✅ Floating, collapsible properties panel with auto-apply
  ✅ Stack-order based priority system (Up/Down buttons)
  ✅ Priority modifier toggle: "Same as Above" (=) vs "Increment" (+)
  ✅ Editable sequence names and effect parameters
  ✅ Real-time statistics display

Navigation & UX:
  ✅ Diagonal mouse wheel scroll with 10% viewport slack
  ✅ Smooth following to time-ordered sequence cascade
  ✅ Flash animation on active sequence change
  ✅ Hoverable sequence names (large centered, fades on hover)
  ✅ Hidden scrollbars (mouse wheel navigation only)
  ✅ Dynamic sequence bounds calculation
  ✅ Cumulative Y positioning (no overlap)

Audio Visualization:
  ✅ Load WAV files via Web Audio API
  ✅ Waveform display above timeline (80px height, cyan color)
  ✅ Scales with zoom (pixels per second)
  ✅ Integration with --dump_wav flag documented
  ✅ Min/max amplitude visualization
  ✅ Crosshair cursor for precision

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CRITICAL BUG FIXES
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  🐛 e.target vs e.currentTarget drag offset bug (erratic jumping)
  🐛 Sequence overlap with dynamic Y positioning
  🐛 Effect relative time calculation errors
  🐛 Left handle constraint preventing negative times
  🐛 Properties panel not triggering re-render

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TECHNICAL IMPLEMENTATION
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Files:
  • tools/timeline_editor/index.html    (~1200 lines)
    - Pure HTML/CSS/JavaScript, no dependencies
    - Works offline, no backend required
    - Web Audio API for waveform decoding
    - Event delegation for nested DOM elements

  • tools/timeline_editor/README.md
    - Usage guide and keyboard shortcuts
    - WAV file generation with --dump_wav integration
    - Format specification reference (doc/SEQUENCE.md)

  • tools/timeline_editor/ROADMAP.md
    - 3-phase development plan (117-161 hour estimate)
    - Phase 1.2: Add Effect button (next priority)
    - Phase 2.5: music.track visualization overlay

Key Patterns:
  • Effect times stored RELATIVE to parent sequence startTime
  • Sequence visual bounds calculated from min/max effect times
  • Stack order determines priority (array index)
  • Snap-to-beat: Math.round(time / beatDuration) * beatDuration
  • Dynamic cumulative Y positioning prevents overlap
  • e.currentTarget vs e.target for proper event delegation

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DOCUMENTATION UPDATES
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TODO.md:
  • Added Task #57 to Recently Completed section
  • Comprehensive feature list and bug fix summary

PROJECT_CONTEXT.md:
  • Added Milestone: Interactive Timeline Editor (February 5, 2026)
  • Documented integration with --dump_wav workflow
  • Next steps: Phase 1.2 and Phase 2.5

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NEXT STEPS
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Phase 1.2: Add Effect Button (Priority: HIGH)
  - Create effects within sequences via UI
  - Modal dialog for effect class/timing/args

Phase 2.5: Music.track Visualization (Priority: MEDIUM)
  - Parse music.track file format
  - Overlay tracker patterns/samples on timeline
  - Align visual sequences with audio events

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IMPACT
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✨ Visual timeline editing now production-ready
✨ Eliminates manual text editing for sequence placement
✨ WAV waveform integration enables precise audio-visual alignment
✨ Snap-to-beat ensures musical timing accuracy
✨ Stack-order priority system simplifies effect layering

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handoff(Claude): Timeline editor Phase 1 milestone complete. All core
editing features working correctly. Waveform visualization integrated
with --dump_wav workflow. Ready for Phase 1.2 (Add Effect button) or
Phase 2 productivity enhancements (undo/redo, multi-select, templates).
No known bugs. Production-ready for demo.seq editing workflow.

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