refactor: replace atomic_double with fixed-point BPM and remove circular dependency

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

engine.c

@@ -157,8 +157,29 @@ static void shutdown_callback(void *arg) {
 
 // Get the next quantization boundary frame
 static jack_nframes_t get_next_quantize_frame(Engine *engine, jack_nframes_t current_frame) {
-    if (!engine->transport) return current_frame;
+    if (!engine->transport || engine->transport->state != TRANSPORT_PLAYING || 
-    return transport_get_next_quantize_frame(engine->transport, current_frame, engine->quantize_mode);
+        engine->quantize_mode == QUANTIZE_OFF) {
+        return current_frame;
+    }
+    
+    // Calculate frames per beat
+    jack_nframes_t frames_per_beat = (jack_nframes_t)engine->transport->samples_per_beat;
+    jack_nframes_t frames_per_bar = frames_per_beat * BEATS_PER_BAR;
+    
+    // Current position in frames
+    jack_nframes_t current_pos = engine->transport->sample_position + current_frame;
+    
+    if (engine->quantize_mode == QUANTIZE_BEAT) {
+        // Next beat boundary
+        jack_nframes_t beat_frames = frames_per_beat;
+        jack_nframes_t next_beat = ((current_pos / beat_frames) + 1) * beat_frames;
+        return next_beat - engine->transport->sample_position;
+    } else {  // QUANTIZE_BAR
+        // Next bar boundary
+        jack_nframes_t bar_frames = frames_per_bar;
+        jack_nframes_t next_bar = ((current_pos / bar_frames) + 1) * bar_frames;
+        return next_bar - engine->transport->sample_position;
+    }
 }
 
 // Queue a trigger for quantization

transport.c

@@ -22,7 +22,8 @@ void transport_init(Transport *transport, jack_nframes_t sample_rate) {
     atomic_store(&transport->bar_position_atomic, 0);
     atomic_store(&transport->sample_position_atomic, 0);
     atomic_store(&transport->clock_source_atomic, CLOCK_SOURCE_INTERNAL);
-    atomic_store(&transport->bpm_atomic, DEFAULT_BPM);
+    transport->bpm_atomic = DEFAULT_BPM;
+    atomic_store(&transport->bpm_atomic_raw, (unsigned int)(DEFAULT_BPM * 100.0));
 }
 
 void transport_cleanup(Transport *transport) {
@@ -100,7 +101,8 @@ void transport_set_bpm(Transport *transport, double bpm) {
     
     transport->bpm = bpm;
     transport->samples_per_beat = (transport->sample_rate * 60.0) / bpm;
-    atomic_store(&transport->bpm_atomic, bpm);
+    transport->bpm_atomic = bpm;
+    atomic_store(&transport->bpm_atomic_raw, (unsigned int)(bpm * 100.0));
 }
 
 double transport_get_bpm(Transport *transport) {
@@ -221,32 +223,6 @@ void transport_reset(Transport *transport) {
     atomic_store(&transport->sample_position_atomic, 0);
 }
 
-jack_nframes_t transport_get_next_quantize_frame(Transport *transport,
-                                                  jack_nframes_t current_frame,
-                                                  QuantizeMode mode) {
-    if (!transport || transport->state != TRANSPORT_PLAYING || mode == QUANTIZE_OFF) {
-        return current_frame;
-    }
-    
-    // Calculate frames per beat
-    jack_nframes_t frames_per_beat = (jack_nframes_t)transport->samples_per_beat;
-    jack_nframes_t frames_per_bar = frames_per_beat * BEATS_PER_BAR;
-    
-    // Current position in frames
-    jack_nframes_t current_pos = transport->sample_position + current_frame;
-    
-    if (mode == QUANTIZE_BEAT) {
-        // Next beat boundary
-        jack_nframes_t beat_frames = frames_per_beat;
-        jack_nframes_t next_beat = ((current_pos / beat_frames) + 1) * beat_frames;
-        return next_beat - transport->sample_position;
-    } else {  // QUANTIZE_BAR
-        // Next bar boundary
-        jack_nframes_t bar_frames = frames_per_bar;
-        jack_nframes_t next_bar = ((current_pos / bar_frames) + 1) * bar_frames;
-        return next_bar - transport->sample_position;
-    }
-}
 
 const char* transport_state_to_string(TransportState state) {
     switch (state) {

transport.h

@@ -45,7 +45,8 @@ typedef struct {
     atomic_uint bar_position_atomic;
     atomic_uint sample_position_atomic;
     atomic_int clock_source_atomic;    // ClockSource
-    atomic_double bpm_atomic;
+    double bpm_atomic;                 // Direct read for audio thread
+    atomic_uint bpm_atomic_raw;        // Fixed-point (BPM * 100) for frontend reads
     
     // JACK ports for MIDI clock output (when master)
     jack_port_t *midi_clock_out_port;
@@ -80,10 +81,6 @@ int transport_process(Transport *transport, jack_nframes_t nframes,
 // Reset position
 void transport_reset(Transport *transport);
 
-// Get next quantization boundary (in frames from current position)
-jack_nframes_t transport_get_next_quantize_frame(Transport *transport, 
-                                                  jack_nframes_t current_frame,
-                                                  QuantizeMode mode);
 
 // Utility
 const char* transport_state_to_string(TransportState state);

tui.c

@@ -284,7 +284,7 @@ static void draw_grid(void) {
              "Transport: %s | Clock: %s | BPM: %.1f | Quantize: %s | Threshold: %u",
              transport_state_to_string(transport_state),
              clock_source_to_string(clock_source),
-             atomic_load(&g_engine->transport->bpm_atomic),
+             (double)atomic_load(&g_engine->transport->bpm_atomic_raw) / 100.0,
              quantize_mode_to_string((QuantizeMode)atomic_load(&g_engine->quantize_mode_atomic)),
              (unsigned int)atomic_load(&g_engine->quantize_threshold_atomic));