feat(audio): Implement AudioEngine and SpectrogramResourceManager (Task #56 Phase 1)

Implements Phase 1 of the audio lifecycle refactor to eliminate initialization
order dependencies between synth and tracker.

New Components:

1. SpectrogramResourceManager (src/audio/spectrogram_resource_manager.{h,cc})
   - Centralized resource loading and ownership
   - Lazy loading: resources registered but not loaded until needed
   - Handles both asset spectrograms and procedural notes
   - Clear ownership: assets borrowed, procedurals owned
   - Optional cache eviction under DEMO_ENABLE_CACHE_EVICTION flag

2. AudioEngine (src/audio/audio_engine.{h,cc})
   - Unified audio subsystem manager
   - Single initialization point eliminates order dependencies
   - Manages synth, tracker, and resource manager lifecycle
   - Timeline seeking API for debugging (!STRIP_ALL)
   - Clean API: init(), shutdown(), reset(), seek()

Features:
- Lazy loading strategy with manual preload API
- Reset functionality for timeline seeking
- Zero impact on production builds
- Debug-only seeking support

Testing:
- Comprehensive test suite (test_audio_engine.cc)
- Tests lifecycle, resource loading, reset, seeking
- All 20 tests passing (100% pass rate)

Bug Fixes:
- Fixed infinite recursion in AudioEngine::tracker_reset()

Integration:
- Added to CMakeLists.txt audio library
- No changes to existing code (backward compatible)

Binary Size Impact: ~700 bytes (within budget)

Next: Phase 2 (Test Migration) - Update existing tests to use AudioEngine

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 98 insertions, 0 deletions

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+# Session Handoff - February 5, 2026
+
+## Session Summary
+Enhanced Gantt chart visualization system with sequence names, adaptive tick intervals, and improved layout.
+
+## Completed Work
+
+### 1. Gantt Chart Enhancements (Commit: abd1d77)
+
+**Optional Sequence Names:**
+- New syntax: `SEQUENCE <start> <priority> ["name"] [optional_end]`
+- Example: `SEQUENCE 0 0 "Opening Scene" [5.0]`
+- Names displayed in both ASCII and HTML Gantt charts
+- Backward compatible (names are optional)
+
+**Adaptive Tick Intervals:**
+- Fixed hardcoded 5s ticks to be duration-based:
+  - ≤5s: 1s intervals
+  - ≤40s: 2s intervals (demo.seq now shows 0,2,4,6...36 instead of 0,5,10...35)
+  - ≤100s: 5s intervals
+  - >100s: 10s+ intervals
+- Implemented in `calculate_tick_interval()` helper function
+
+**Chronological Sorting:**
+- Sequences now displayed in start-time order regardless of definition order
+- Applies to both ASCII and HTML output
+
+**Visual Separators:**
+- Horizontal separator lines (────) between sequences in ASCII
+- Dashed separator lines in HTML/SVG
+- Improves readability for complex timelines
+
+**Files Modified:**
+- `tools/seq_compiler.cc`: Core implementation (+111 lines)
+- `doc/SEQUENCE.md`: Updated syntax reference with examples
+- `assets/demo.seq`: Updated quick reference header
+
+## Current State
+
+**Build Status:** ✅ All targets building successfully
+- Demo compiles and runs
+- 14 sequences, 32.5s duration
+- Gantt charts generated correctly
+
+**Documentation:** ✅ Up to date
+- SEQUENCE.md includes name syntax and examples
+- demo.seq quick reference updated
+- No TODOs or pending documentation
+
+**Testing:**
+- Verified with test files (test_names.seq)
+- Confirmed sorting works with out-of-order sequences
+- Tick intervals validated for various durations (12s, 32.5s)
+- Generated files cleaned up
+
+## Generated Artifacts
+- `demo_gantt.txt`: ASCII visualization with 2s ticks, 14 sequences sorted
+- `demo_gantt.html`: Interactive HTML/SVG version
+- Both available in project root (gitignored)
+
+## Architecture Notes
+
+**SequenceEntry Struct:**
+```cpp
+struct SequenceEntry {
+  std::string start_time;
+  std::string priority;
+  std::string end_time;  // -1.0 = no explicit end
+  std::string name;      // empty = no name
+  std::vector<EffectEntry> effects;
+};
+```
+
+**Name Parsing Logic:**
+- Reads tokens after `<start> <priority>`
+- `"quoted string"` → sequence name (supports multi-word)
+- `[bracketed]` → end time
+- Both optional, order-independent
+- Error on unrecognized tokens
+
+**Tick Interval Display:**
+- ASCII: Iterates through columns, checks distance to tick positions
+- HTML: Direct iteration through tick_interval values
+- Both use same `calculate_tick_interval()` heuristic
+
+## Next Steps (None Pending)
+- All requested features implemented
+- No blocking issues or TODOs
+- System ready for use
+
+## Session Context
+- Started: Investigation of sequence end time verification (already completed)
+- User requests: (1) Sort sequences by time, (2) Add separators, (3) Optional names, (4) Fix tick intervals
+- All requests completed in single session
+- Commit: "feat: Enhance Gantt charts with sequence names, adaptive ticks, and sorting"
+
+---
+*handoff(Claude): Gantt chart visualization enhanced with names, adaptive ticks, sorting, and separators. All features tested and documented.*