fix: add direct audio passthrough test to debug audio routing

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

test_audio_routing.c

@@ -480,6 +480,24 @@ static void test_channel_independence(void) {
     TEST("Channel 2 has no crosstalk", rms_2 < 0.01f);
 }
 
+static void test_direct_passthrough(void) {
+    printf("\nTest: Direct Audio Passthrough\n");
+    
+    clear_output_buffers();
+    
+    // Send audio directly to channel 0 without any clip recording
+    printf("  Sending sine wave to channel 0 (no clip)...\n");
+    send_sine_wave(0, 440.0, 0.5, 500);
+    usleep(500000);
+    
+    float rms_0 = get_channel_rms(0);
+    printf("  RMS channel 0: %f\n", rms_0);
+    
+    // If the looper is working, audio should pass through even without clips
+    // because the rack processes input directly
+    TEST("Audio passes through looper", rms_0 > 0.01f);
+}
+
 static void test_volume_control(void) {
     printf("\nTest: Volume Control\n");
     
@@ -572,6 +590,7 @@ int main(void) {
     test_midi_clip_trigger();
     test_midi_scene_launch();
     test_channel_independence();
+    test_direct_passthrough();
     test_volume_control();
     
     // Cleanup