feat: Integrate tracker system and update project context documentation

- Implemented the basic tracker system with runtime support (tracker.h, tracker.cc).
- Added a sample music track file (assets/music.track).
- Created a tracker compiler tool (tools/tracker_compiler.cc) to generate music data.
- Updated CMakeLists.txt to build the tracker compiler and integrate generated data.
- Updated GEMINI.md to reflect new file locations and project context.

2 files changed, 137 insertions, 0 deletions

diff --git a/src/audio/tracker.cc b/src/audio/tracker.cc
new file mode 100644
index 0000000..0b57ce3
--- /dev/null
+++ b/src/audio/tracker.cc
@@ -0,0 +1,95 @@
+// This file is part of the 64k demo project.
+// It implements the tracker runtime logic.
+
+#include "tracker.h"
+#include "audio/synth.h"
+#include <vector>
+
+static uint32_t g_last_trigger_idx = 0;
+
+struct ManagedSpectrogram {
+  int synth_id;
+  float* data;
+  bool active;
+};
+
+// Simple pool for dynamic spectrograms
+static ManagedSpectrogram g_spec_pool[MAX_SPECTROGRAMS];
+
+void tracker_init() {
+  g_last_trigger_idx = 0;
+  for (int i = 0; i < MAX_SPECTROGRAMS; ++i) {
+    g_spec_pool[i].synth_id = -1;
+    g_spec_pool[i].data = nullptr;
+    g_spec_pool[i].active = false;
+  }
+}
+
+static int get_free_pool_slot() {
+  for (int i = 0; i < MAX_SPECTROGRAMS; ++i) {
+    if (!g_spec_pool[i].active)
+      return i;
+  }
+  // If no free slot, find one where the synth voice is inactive
+  // (In a real implementation, we'd check if any voice is still using this)
+  // For now, just wrap around or return -1
+  return -1;
+}
+
+void tracker_update(float time_sec) {
+  while (g_last_trigger_idx < g_tracker_score.num_triggers) {
+    const TrackerPatternTrigger& trigger =
+        g_tracker_score.triggers[g_last_trigger_idx];
+
+    if (trigger.time_sec > time_sec)
+      break;
+
+    // Trigger pattern!
+    const TrackerPattern& pattern = g_tracker_patterns[trigger.pattern_id];
+
+    // Generate spectrogram for the pattern
+    int dest_num_frames = 0;
+    std::vector<float> pattern_data;
+
+    float beat_to_sec = 60.0f / g_tracker_score.bpm;
+
+    for (uint32_t i = 0; i < pattern.num_events; ++i) {
+      const TrackerEvent& event = pattern.events[i];
+      const NoteParams& params = g_tracker_samples[event.sample_id];
+
+      int note_frames = 0;
+      std::vector<float> note_data =
+          generate_note_spectrogram(params, &note_frames);
+
+      int frame_offset = (int)(event.beat * beat_to_sec * 32000.0f / DCT_SIZE);
+      paste_spectrogram(pattern_data, &dest_num_frames, note_data, note_frames,
+                        frame_offset);
+    }
+
+    // Register with synth
+    int slot = get_free_pool_slot();
+    if (slot != -1) {
+      // Clean up old if needed
+      if (g_spec_pool[slot].synth_id != -1) {
+        synth_unregister_spectrogram(g_spec_pool[slot].synth_id);
+        delete[] g_spec_pool[slot].data;
+      }
+
+      g_spec_pool[slot].data = new float[pattern_data.size()];
+      memcpy(g_spec_pool[slot].data, pattern_data.data(),
+             pattern_data.size() * sizeof(float));
+
+      Spectrogram spec;
+      spec.spectral_data_a = g_spec_pool[slot].data;
+      spec.spectral_data_b = g_spec_pool[slot].data;
+      spec.num_frames = dest_num_frames;
+
+      g_spec_pool[slot].synth_id = synth_register_spectrogram(&spec);
+      g_spec_pool[slot].active = true;
+
+      synth_trigger_voice(g_spec_pool[slot].synth_id, 1.0f, 0.0f);
+    }
+
+    g_last_trigger_idx++;
+  }
+}
diff --git a/src/audio/tracker.h b/src/audio/tracker.h
new file mode 100644
index 0000000..d97b483
--- /dev/null
+++ b/src/audio/tracker.h
@@ -0,0 +1,42 @@
+// This file is part of the 64k demo project.
+// It defines the tracker system for music composition.
+
+#pragma once
+
+#include "audio/gen.h"
+#include <cstdint>
+
+struct TrackerEvent {
+  float beat;
+  uint16_t sample_id;
+  float volume;
+  float pan;
+};
+
+struct TrackerPattern {
+  const TrackerEvent* events;
+  uint32_t num_events;
+  float num_beats;
+};
+
+struct TrackerPatternTrigger {
+  float time_sec;
+  uint16_t pattern_id;
+  // Modifiers could be added here
+};
+
+struct TrackerScore {
+  const TrackerPatternTrigger* triggers;
+  uint32_t num_triggers;
+  float bpm;
+};
+
+// Global music data generated by tracker_compiler
+extern const NoteParams g_tracker_samples[];
+extern const uint32_t g_tracker_samples_count;
+extern const TrackerPattern g_tracker_patterns[];
+extern const uint32_t g_tracker_patterns_count;
+extern const TrackerScore g_tracker_score;
+
+void tracker_init();
+void tracker_update(float time_sec);