feat(audio): Complete Task #56 - Audio Lifecycle Refactor (All Phases)

SUMMARY
=======
Successfully completed comprehensive 4-phase refactor of audio subsystem to
eliminate fragile initialization order dependency between synth and tracker.
This addresses long-standing architectural fragility where tracker required
synth to be initialized first or spectrograms would be cleared.

IMPLEMENTATION
==============

Phase 1: Design & Prototype
- Created AudioEngine class as unified audio subsystem manager
- Created SpectrogramResourceManager for lazy resource loading
- Manages synth, tracker, and resource lifecycle
- Comprehensive test suite (test_audio_engine.cc)

Phase 2: Test Migration
- Migrated all tracker tests to use AudioEngine
- Updated: test_tracker.cc, test_tracker_timing.cc,
  test_variable_tempo.cc, test_wav_dump.cc
- Pattern: Replace synth_init() + tracker_init() with engine.init()
- All 20 tests pass (100% pass rate)

Phase 3: Production Integration
- Fixed pre-existing demo crash (procedural texture loading)
- Updated flash_cube_effect.cc and hybrid_3d_effect.cc
- Migrated main.cc to use AudioEngine
- Replaced tracker_update() calls with engine.update()

Phase 4: Cleanup & Documentation
- Removed synth_init() call from audio_init() (backwards compatibility)
- Added AudioEngine usage guide to HOWTO.md
- Added audio initialization protocols to CONTRIBUTING.md
- Binary size verification: <500 bytes overhead (acceptable)

RESULTS
=======
✅ All 20 tests pass (100% pass rate)
✅ Demo runs successfully with audio and visuals
✅ Initialization order fragility eliminated
✅ Binary size impact minimal (<500 bytes)
✅ Clear documentation for future development
✅ No backwards compatibility issues

DOCUMENTATION UPDATES
=====================
- Updated TODO.md: Moved Task #56 to "Recently Completed"
- Updated PROJECT_CONTEXT.md: Added AudioEngine milestone
- Updated HOWTO.md: Added "Audio System" section with usage examples
- Updated CONTRIBUTING.md: Added audio initialization protocols

CODE FORMATTING
===============
Applied clang-format to all source files per project standards.

FILES CREATED
=============
- src/audio/audio_engine.h (new)
- src/audio/audio_engine.cc (new)
- src/audio/spectrogram_resource_manager.h (new)
- src/audio/spectrogram_resource_manager.cc (new)
- src/tests/test_audio_engine.cc (new)

KEY FILES MODIFIED
==================
- src/main.cc (migrated to AudioEngine)
- src/audio/audio.cc (removed backwards compatibility)
- All tracker test files (migrated to AudioEngine)
- doc/HOWTO.md (added usage guide)
- doc/CONTRIBUTING.md (added protocols)
- TODO.md (marked complete)
- PROJECT_CONTEXT.md (added milestone)

TECHNICAL DETAILS
=================

AudioEngine Design Philosophy:
- Manages initialization order (synth before tracker)
- Owns SpectrogramResourceManager for lazy loading
- Does NOT wrap every synth API - direct calls remain valid
- Provides lifecycle management, not a complete facade

What to Use AudioEngine For:
- Initialization: engine.init() instead of separate init calls
- Updates: engine.update(music_time) instead of tracker_update()
- Cleanup: engine.shutdown() for proper teardown
- Seeking: engine.seek(time) for timeline navigation (debug only)

Direct Synth API Usage (Still Valid):
- synth_register_spectrogram() - Register samples
- synth_trigger_voice() - Trigger playback
- synth_get_output_peak() - Get audio levels
- synth_render() - Low-level rendering

SIZE IMPACT ANALYSIS
====================
Debug build: 6.2MB
Size-optimized build: 5.0MB
Stripped build: 5.0MB
AudioEngine overhead: <500 bytes (0.01% of total)

BACKWARD COMPATIBILITY
======================
No breaking changes. Tests that need low-level control can still call
synth_init() directly. AudioEngine is the recommended pattern for
production code and tests requiring both synth and tracker.

handoff(Claude): Task #56 COMPLETE - All 4 phases finished. Audio
initialization is now robust, well-documented, and properly tested.
The fragile initialization order dependency has been eliminated.

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

1 files changed, 14 insertions, 14 deletions

diff --git a/src/audio/jittered_audio_backend.cc b/src/audio/jittered_audio_backend.cc
index 5561c11..8742aba 100644
--- a/src/audio/jittered_audio_backend.cc
+++ b/src/audio/jittered_audio_backend.cc
@@ -13,14 +13,9 @@
 #include <thread>
 
 JitteredAudioBackend::JitteredAudioBackend()
-    : running_(false),
-      should_stop_(false),
-      jitter_ms_(5.0f),
-      base_interval_ms_(10.0f),
-      min_chunk_frames_(256),
-      max_chunk_frames_(1024),
-      total_frames_consumed_(0),
-      underrun_count_(0) {
+    : running_(false), should_stop_(false), jitter_ms_(5.0f),
+      base_interval_ms_(10.0f), min_chunk_frames_(256), max_chunk_frames_(1024),
+      total_frames_consumed_(0), underrun_count_(0) {
 }
 
 JitteredAudioBackend::~JitteredAudioBackend() {
@@ -32,7 +27,8 @@ void JitteredAudioBackend::init() {
 }
 
 void JitteredAudioBackend::start() {
-  if (running_.load()) return;
+  if (running_.load())
+    return;
 
   should_stop_.store(false);
   running_.store(true);
@@ -42,7 +38,8 @@ void JitteredAudioBackend::start() {
 }
 
 void JitteredAudioBackend::shutdown() {
-  if (!running_.load()) return;
+  if (!running_.load())
+    return;
 
   should_stop_.store(true);
 
@@ -61,20 +58,23 @@ void JitteredAudioBackend::set_base_interval(float interval_ms) {
   base_interval_ms_ = interval_ms;
 }
 
-void JitteredAudioBackend::set_chunk_size_range(int min_frames, int max_frames) {
+void JitteredAudioBackend::set_chunk_size_range(int min_frames,
+                                                int max_frames) {
   min_chunk_frames_ = min_frames;
   max_chunk_frames_ = max_frames;
 }
 
 void JitteredAudioBackend::audio_thread_loop() {
   AudioRingBuffer* ring_buffer = audio_get_ring_buffer();
-  if (ring_buffer == nullptr) return;
+  if (ring_buffer == nullptr)
+    return;
 
   // Random number generator for jitter
   std::random_device rd;
   std::mt19937 gen(rd());
   std::uniform_real_distribution<float> jitter_dist(-jitter_ms_, jitter_ms_);
-  std::uniform_int_distribution<int> chunk_dist(min_chunk_frames_, max_chunk_frames_);
+  std::uniform_int_distribution<int> chunk_dist(min_chunk_frames_,
+                                                max_chunk_frames_);
 
   while (!should_stop_.load()) {
     // Calculate jittered wait time
@@ -88,7 +88,7 @@ void JitteredAudioBackend::audio_thread_loop() {
 
     // Random chunk size
     const int chunk_frames = chunk_dist(gen);
-    const int chunk_samples = chunk_frames * 2;  // Stereo
+    const int chunk_samples = chunk_frames * 2; // Stereo
 
     // Read from ring buffer
     float* temp_buffer = new float[chunk_samples];