fix: use pointer to dispatcher state in process callback for real-time access

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

dispatcher.c

@@ -117,6 +117,10 @@ void dispatcher_get_state(AppState *out) {
     pthread_mutex_unlock(&dispatcher.state_mutex);
 }
 
+AppState* dispatcher_get_state_ptr(void) {
+    return &dispatcher.state;
+}
+
 // ============================================================
 // Reducer implementation
 // ============================================================

dispatcher.h

@@ -210,6 +210,11 @@ void dispatcher_stop(void);
 // Get current state (thread-safe snapshot)
 void dispatcher_get_state(AppState *out);
 
+// Get pointer to dispatcher's state (for real-time threads that can't block)
+// WARNING: This is NOT thread-safe. Only use in JACK process callback
+// which is serialized per client.
+AppState* dispatcher_get_state_ptr(void);
+
 // ============================================================
 // Reducer - pure function
 // ============================================================

engine.c

@@ -28,9 +28,8 @@ static int process_callback(jack_nframes_t nframes, void *arg) {
     
     jack_midi_clear_buffer(midi_out_buf);
     
-    // Get state snapshot for reads
-    AppState state;
-    dispatcher_get_state(&state);
+    // Get pointer to dispatcher's state for real-time access
+    AppState *state = engine->state;
     
     // Process MIDI input
     int event_index;
@@ -100,7 +99,7 @@ static int process_callback(jack_nframes_t nframes, void *arg) {
         for (int s = 0; s < MAX_SCENES; s++) {
             for (int g = 0; g < 8; g++) {
                 int clip_idx = g * GRID_ROWS * GRID_COLS + s * GRID_COLS + ch;
-                MidiClip *mclip = &state.midi_clips[clip_idx];
+                MidiClip *mclip = &state->midi_clips[clip_idx];
                 
                 if (mclip->state == CLIP_LOOPING && mclip->event_count > 0 && mclip->events != NULL) {
                     if (mclip->read_index < mclip->event_count) {
@@ -142,7 +141,7 @@ static int process_callback(jack_nframes_t nframes, void *arg) {
                 // Iterate over all grids for this scene and channel
                 for (int g = 0; g < 8; g++) {
                     int clip_idx = g * GRID_ROWS * GRID_COLS + s * GRID_COLS + ch;
-                    Clip *clip = &state.clips[clip_idx];
+                    Clip *clip = &state->clips[clip_idx];
                     
                     if (clip->state == CLIP_RECORDING) {
                         if (clip->write_position < MAX_BUFFER_SIZE && clip->buffer != NULL) {
@@ -237,6 +236,9 @@ int engine_init(Engine *engine, const char *client_name, DispatchFn dispatch) {
     carla_init(&engine->carla_host, engine->client);
     carla_scan_plugins(&engine->carla_host);
     
+    // Get pointer to dispatcher's state for real-time access
+    engine->state = dispatcher_get_state_ptr();
+    
     return 0;
 }
 

engine.h

@@ -21,6 +21,8 @@ typedef struct {
     bool running;
     
     CarlaHost carla_host;  // Carla host state for plugin management
+    
+    AppState *state;  // Pointer to dispatcher's state (for real-time access)
 } Engine;
 
 int engine_init(Engine *engine, const char *client_name, DispatchFn dispatch);