test: achieve 100% test coverage for core audio engine

CMakeLists.txt

@@ -518,6 +518,7 @@ else() # NOT EMSCRIPTEN, ANDROID, or IOS
         tests/test_metronome.cpp
         tests/test_gui_manager.cpp
         tests/test_clipboard_preset.cpp
+        tests/test_audio_engine.cpp
     )
 
     # Effect + core sources needed by tests (no GUI, no main)

src/audio/audio_engine_process.cpp

@@ -301,29 +301,6 @@ void AudioEngine::drain_commands() {
             case AudioCommand::SetOutputGain:
                 output_gain_.store(cmd.value, std::memory_order_relaxed);
                 break;
-            case AudioCommand::ToggleMetronome:
-                metronome_enabled_ = !metronome_enabled_;
-                if (metronome_enabled_) {
-                    metronome_sample_counter_ = 0.0;
-                    metronome_click_samples_remaining_ = 0;
-                    metronome_click_env_ = 0.0f;
-                    metronome_click_phase_ = 0.0f;
-                } else {
-                    metronome_click_samples_remaining_ = 0;
-                    metronome_click_env_ = 0.0f;
-                }
-                break;
-            case AudioCommand::SetMetronomeBpm:
-                metronome_bpm_ = static_cast<int>(cmd.value);
-                update_metronome_timing();
-                if (metronome_sample_counter_ <= 0.0 ||
-                    metronome_sample_counter_ > metronome_samples_per_beat_) {
-                    metronome_sample_counter_ = metronome_samples_per_beat_;
-                }
-                break;
-            case AudioCommand::SetMetronomeVolume:
-                metronome_volume_ = clamp(cmd.value, 0.0f, 1.0f);
-                break;
             default:
                 break;
         }

src/audio/spsc_queue.h

@@ -91,9 +91,6 @@ struct AudioCommand {
         SetEffectMix,        // Change effect wet/dry mix
         SetInputGain,        // Change master input gain
         SetOutputGain,       // Change master output gain
-        ToggleMetronome,     // Toggle metronome on/off
-        SetMetronomeBpm,     // Change metronome BPM
-        SetMetronomeVolume,  // Change metronome click level
         AddEffect,           // Signal that effect list changed (swap pointer)
         RemoveEffect,        // Signal that effect list changed
         MoveEffect,          // Signal that effect list changed