feat: implement undo/redo system with history tracking and tests

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

engine.c

@@ -333,6 +333,17 @@ void engine_process_commands(Engine *engine) {
                 if (cmd.index < 0 || cmd.index >= MAX_CLIPS) break;
                 Clip *clip = &engine->clips[cmd.index];
                 
+                // Record undo action
+                UndoAction action;
+                action.type = ACTION_TRIGGER_CLIP;
+                action.index = cmd.index;
+                action.value = 0;
+                action.previous_state = clip->state;
+                action.previous_buffer_size = clip->buffer_size;
+                action.previous_write_position = clip->write_position;
+                action.previous_read_position = clip->read_position;
+                engine_push_undo_action(engine, &action);
+                
                 switch (clip->state) {
                     case CLIP_EMPTY:
                         clip->state = CLIP_RECORDING;
@@ -359,6 +370,14 @@ void engine_process_commands(Engine *engine) {
             
             case CMD_TRIGGER_SCENE: {
                 if (cmd.index < 0 || cmd.index >= MAX_SCENES) break;
+                
+                // Record undo action
+                UndoAction action;
+                action.type = ACTION_TRIGGER_SCENE;
+                action.index = cmd.index;
+                action.value = 0;
+                engine_push_undo_action(engine, &action);
+                
                 for (int ch = 0; ch < MAX_CHANNELS; ch++) {
                     int clip_idx = CLIP_INDEX(cmd.index, ch);
                     Clip *clip = &engine->clips[clip_idx];
@@ -391,6 +410,18 @@ void engine_process_commands(Engine *engine) {
             case CMD_RESET_CLIP: {
                 if (cmd.index < 0 || cmd.index >= MAX_CLIPS) break;
                 Clip *clip = &engine->clips[cmd.index];
+                
+                // Record undo action
+                UndoAction action;
+                action.type = ACTION_RESET_CLIP;
+                action.index = cmd.index;
+                action.value = 0;
+                action.previous_state = clip->state;
+                action.previous_buffer_size = clip->buffer_size;
+                action.previous_write_position = clip->write_position;
+                action.previous_read_position = clip->read_position;
+                engine_push_undo_action(engine, &action);
+                
                 clip->state = CLIP_EMPTY;
                 clip->buffer_size = 0;
                 clip->write_position = 0;
@@ -399,15 +430,51 @@ void engine_process_commands(Engine *engine) {
                 break;
             }
             
-            case CMD_SET_QUANTIZE_MODE:
-                engine->quantize_mode = (QuantizeMode)cmd.index;
-                break;
+            case CMD_SET_QUANTIZE_MODE: {
+                QuantizeMode new_mode = (QuantizeMode)cmd.index;
                 
-            case CMD_SET_QUANTIZE_THRESHOLD:
-                engine->quantize_threshold = cmd.value;
-                break;
+                // Record undo action
+                UndoAction action;
+                action.type = ACTION_SET_QUANTIZE_MODE;
+                action.index = (int)new_mode;
+                action.value = 0;
+                action.previous_quantize_mode = engine->quantize_mode;
+                engine_push_undo_action(engine, &action);
+                
+                engine->quantize_mode = new_mode;
+                atomic_store(&engine->quantize_mode_atomic, (int)new_mode);
+                break;
+            }
+                
+            case CMD_SET_QUANTIZE_THRESHOLD: {
+                jack_nframes_t new_threshold = cmd.value;
+                
+                // Record undo action
+                UndoAction action;
+                action.type = ACTION_SET_QUANTIZE_THRESHOLD;
+                action.index = 0;
+                action.value = new_threshold;
+                action.previous_quantize_threshold = engine->quantize_threshold;
+                engine_push_undo_action(engine, &action);
+                
+                engine->quantize_threshold = new_threshold;
+                atomic_store(&engine->quantize_threshold_atomic, new_threshold);
+                break;
+            }
+                
+            case CMD_RESET_TRANSPORT: {
+                // Record undo action
+                UndoAction action;
+                action.type = ACTION_RESET_TRANSPORT;
+                action.index = 0;
+                action.value = 0;
+                action.previous_rolling = engine->transport.rolling;
+                action.previous_clock_count = engine->transport.clock_count;
+                action.previous_beat_position = engine->transport.beat_position;
+                action.previous_bar_position = engine->transport.bar_position;
+                action.previous_sample_position = engine->transport.sample_position;
+                engine_push_undo_action(engine, &action);
                 
-            case CMD_RESET_TRANSPORT:
                 engine->transport.rolling = false;
                 engine->transport.clock_count = 0;
                 engine->transport.beat_position = 0;
@@ -419,6 +486,16 @@ void engine_process_commands(Engine *engine) {
                 atomic_store(&engine->transport_bar_position, 0);
                 atomic_store(&engine->transport_sample_position, 0);
                 break;
+            }
+        }
+        
+            case CMD_UNDO:
+                engine_undo(engine);
+                break;
+                
+            case CMD_REDO:
+                engine_redo(engine);
+                break;
         }
         
         read++;
@@ -428,6 +505,159 @@ void engine_process_commands(Engine *engine) {
     atomic_store(&q->read_index, read);
 }
 
+// Push an action to the undo history
+void engine_push_undo_action(Engine *engine, UndoAction *action) {
+    if (!engine || !action) return;
+    
+    UndoHistory *history = &engine->undo_history;
+    
+    // If we've undone some actions, clear the redo history
+    if (history->redo_index > history->undo_index) {
+        history->redo_index = history->undo_index;
+    }
+    
+    // Add action at current undo position
+    int slot = history->undo_index % MAX_UNDO_HISTORY;
+    history->actions[slot] = *action;
+    history->undo_index++;
+    history->redo_index = history->undo_index;
+    
+    if (history->count < MAX_UNDO_HISTORY) {
+        history->count++;
+    }
+}
+
+// Undo the last action
+void engine_undo(Engine *engine) {
+    if (!engine) return;
+    
+    UndoHistory *history = &engine->undo_history;
+    if (history->undo_index <= 0) return;  // Nothing to undo
+    
+    int slot = (history->undo_index - 1) % MAX_UNDO_HISTORY;
+    UndoAction *action = &history->actions[slot];
+    
+    switch (action->type) {
+        case ACTION_TRIGGER_CLIP: {
+            int clip_idx = action->index;
+            engine->clips[clip_idx].state = action->previous_state;
+            engine->clips[clip_idx].buffer_size = action->previous_buffer_size;
+            engine->clips[clip_idx].write_position = action->previous_write_position;
+            engine->clips[clip_idx].read_position = action->previous_read_position;
+            break;
+        }
+            
+        case ACTION_TRIGGER_SCENE: {
+            int scene_idx = action->index;
+            for (int ch = 0; ch < MAX_CHANNELS; ch++) {
+                int clip_idx = CLIP_INDEX(scene_idx, ch);
+                engine->clips[clip_idx].state = CLIP_EMPTY;
+            }
+            break;
+        }
+            
+        case ACTION_RESET_CLIP: {
+            int clip_idx = action->index;
+            engine->clips[clip_idx].state = action->previous_state;
+            engine->clips[clip_idx].buffer_size = action->previous_buffer_size;
+            engine->clips[clip_idx].write_position = action->previous_write_position;
+            engine->clips[clip_idx].read_position = action->previous_read_position;
+            break;
+        }
+            
+        case ACTION_SET_QUANTIZE_MODE: {
+            engine->quantize_mode = action->previous_quantize_mode;
+            atomic_store(&engine->quantize_mode_atomic, (int)action->previous_quantize_mode);
+            break;
+        }
+            
+        case ACTION_SET_QUANTIZE_THRESHOLD: {
+            engine->quantize_threshold = action->previous_quantize_threshold;
+            atomic_store(&engine->quantize_threshold_atomic, action->previous_quantize_threshold);
+            break;
+        }
+            
+        case ACTION_RESET_TRANSPORT: {
+            engine->transport.rolling = action->previous_rolling;
+            engine->transport.clock_count = action->previous_clock_count;
+            engine->transport.beat_position = action->previous_beat_position;
+            engine->transport.bar_position = action->previous_bar_position;
+            engine->transport.sample_position = action->previous_sample_position;
+            atomic_store(&engine->transport_rolling, action->previous_rolling ? 1 : 0);
+            atomic_store(&engine->transport_clock_count, action->previous_clock_count);
+            atomic_store(&engine->transport_beat_position, action->previous_beat_position);
+            atomic_store(&engine->transport_bar_position, action->previous_bar_position);
+            atomic_store(&engine->transport_sample_position, action->previous_sample_position);
+            break;
+        }
+    }
+    
+    history->undo_index--;
+}
+
+// Redo the last undone action
+void engine_redo(Engine *engine) {
+    if (!engine) return;
+    
+    UndoHistory *history = &engine->undo_history;
+    if (history->redo_index <= history->undo_index) return;  // Nothing to redo
+    
+    int slot = history->undo_index % MAX_UNDO_HISTORY;
+    UndoAction *action = &history->actions[slot];
+    
+    switch (action->type) {
+        case ACTION_TRIGGER_CLIP: {
+            int clip_idx = action->index;
+            // Re-apply the trigger
+            engine_trigger_clip(engine, clip_idx);
+            engine_process_commands(engine);
+            break;
+        }
+            
+        case ACTION_TRIGGER_SCENE: {
+            int scene_idx = action->index;
+            engine_trigger_scene(engine, scene_idx);
+            engine_process_commands(engine);
+            break;
+        }
+            
+        case ACTION_RESET_CLIP: {
+            int clip_idx = action->index;
+            engine_reset_clip(engine, clip_idx);
+            engine_process_commands(engine);
+            break;
+        }
+            
+        case ACTION_SET_QUANTIZE_MODE: {
+            engine->quantize_mode = (QuantizeMode)action->index;
+            atomic_store(&engine->quantize_mode_atomic, action->index);
+            break;
+        }
+            
+        case ACTION_SET_QUANTIZE_THRESHOLD: {
+            engine->quantize_threshold = action->value;
+            atomic_store(&engine->quantize_threshold_atomic, action->value);
+            break;
+        }
+            
+        case ACTION_RESET_TRANSPORT: {
+            engine->transport.rolling = true;
+            engine->transport.clock_count = 0;
+            engine->transport.beat_position = 0;
+            engine->transport.bar_position = 0;
+            engine->transport.sample_position = 0;
+            atomic_store(&engine->transport_rolling, 1);
+            atomic_store(&engine->transport_clock_count, 0);
+            atomic_store(&engine->transport_beat_position, 0);
+            atomic_store(&engine->transport_bar_position, 0);
+            atomic_store(&engine->transport_sample_position, 0);
+            break;
+        }
+    }
+    
+    history->undo_index++;
+}
+
 int engine_init(Engine *engine, const char *client_name) {
     if (!engine || !client_name) return -1;
     
@@ -438,6 +668,11 @@ int engine_init(Engine *engine, const char *client_name) {
     engine->quantize_threshold = 0;
     engine->queued_triggers = NULL;
     
+    // Initialize undo history
+    engine->undo_history.undo_index = 0;
+    engine->undo_history.redo_index = 0;
+    engine->undo_history.count = 0;
+    
     // Initialize command queue
     command_queue_init(&engine->command_queue);
     
@@ -647,3 +882,13 @@ const char* quantize_mode_to_string(QuantizeMode mode) {
         default: return "Unknown";
     }
 }
+
+void engine_undo_action(Engine *engine) {
+    if (!engine) return;
+    engine_submit_command(engine, CMD_UNDO, 0, 0);
+}
+
+void engine_redo_action(Engine *engine) {
+    if (!engine) return;
+    engine_submit_command(engine, CMD_REDO, 0, 0);
+}

engine.h

@@ -56,9 +56,49 @@ typedef enum {
     CMD_RESET_CLIP,
     CMD_SET_QUANTIZE_MODE,
     CMD_SET_QUANTIZE_THRESHOLD,
-    CMD_RESET_TRANSPORT
+    CMD_RESET_TRANSPORT,
+    CMD_UNDO,
+    CMD_REDO
 } CommandType;
 
+// Undo/Redo action types
+typedef enum {
+    ACTION_TRIGGER_CLIP,
+    ACTION_TRIGGER_SCENE,
+    ACTION_RESET_CLIP,
+    ACTION_SET_QUANTIZE_MODE,
+    ACTION_SET_QUANTIZE_THRESHOLD,
+    ACTION_RESET_TRANSPORT
+} ActionType;
+
+// Undo/Redo action record
+typedef struct {
+    ActionType type;
+    int index;           // clip_index, scene_index, or mode value
+    jack_nframes_t value; // threshold value or other numeric param
+    ClipState previous_state;  // For clip state changes
+    size_t previous_buffer_size;
+    size_t previous_write_position;
+    size_t previous_read_position;
+    bool previous_rolling;
+    uint32_t previous_clock_count;
+    uint32_t previous_beat_position;
+    uint32_t previous_bar_position;
+    uint32_t previous_sample_position;
+    QuantizeMode previous_quantize_mode;
+    jack_nframes_t previous_quantize_threshold;
+} UndoAction;
+
+// Undo/Redo history
+#define MAX_UNDO_HISTORY 256
+
+typedef struct {
+    UndoAction actions[MAX_UNDO_HISTORY];
+    int undo_index;  // Points to next action to undo
+    int redo_index;  // Points to next action to redo
+    int count;       // Total actions in history
+} UndoHistory;
+
 typedef struct {
     CommandType type;
     int index;           // clip_index, scene_index, or mode value
@@ -115,6 +155,9 @@ typedef struct {
     atomic_uint quantize_threshold_atomic;
     
     bool running;
+    
+    // Undo/Redo
+    UndoHistory undo_history;
 } Engine;
 
 // Engine lifecycle
@@ -150,4 +193,11 @@ const char* clip_state_to_string(ClipState state);
 uint8_t clip_state_to_velocity(ClipState state);
 const char* quantize_mode_to_string(QuantizeMode mode);
 
+// Undo/Redo
+void engine_undo(Engine *engine);
+void engine_redo(Engine *engine);
+void engine_push_undo_action(Engine *engine, UndoAction *action);
+void engine_undo_action(Engine *engine);
+void engine_redo_action(Engine *engine);
+
 #endif // ENGINE_H

test_tui.c

@@ -1211,6 +1211,379 @@ void test_remark_existing_mark(void) {
     printf("PASSED\n");
 }
 
+// Test 53: Undo single clip trigger
+void test_undo_single_trigger(void) {
+    printf("Test 53: Undo single clip trigger... ");
+    Engine *engine = create_test_engine();
+    
+    // Start with empty clip
+    int clip_idx = 10;
+    assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    
+    // Trigger clip (empty -> recording)
+    engine_trigger_clip(engine, clip_idx);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_RECORDING);
+    
+    // Undo: should go back to empty
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 54: Undo multiple clip triggers
+void test_undo_multiple_triggers(void) {
+    printf("Test 54: Undo multiple clip triggers... ");
+    Engine *engine = create_test_engine();
+    
+    int clip1 = 10, clip2 = 11, clip3 = 12;
+    
+    // Trigger three clips
+    engine_trigger_clip(engine, clip1);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    
+    engine_trigger_clip(engine, clip2);
+    engine_process_commands(engine);
+    assert(engine->clips[clip2].state == CLIP_RECORDING);
+    
+    engine_trigger_clip(engine, clip3);
+    engine_process_commands(engine);
+    assert(engine->clips[clip3].state == CLIP_RECORDING);
+    
+    // Undo last action: clip3 should go back to empty
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip3].state == CLIP_EMPTY);
+    assert(engine->clips[clip2].state == CLIP_RECORDING);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    
+    // Undo again: clip2 should go back to empty
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip2].state == CLIP_EMPTY);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 55: Redo single undo
+void test_redo_single_undo(void) {
+    printf("Test 55: Redo single undo... ");
+    Engine *engine = create_test_engine();
+    
+    int clip_idx = 10;
+    
+    // Trigger clip
+    engine_trigger_clip(engine, clip_idx);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_RECORDING);
+    
+    // Undo
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    
+    // Redo: should go back to recording
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_RECORDING);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 56: Redo after multiple undos
+void test_redo_multiple_undos(void) {
+    printf("Test 56: Redo after multiple undos... ");
+    Engine *engine = create_test_engine();
+    
+    int clip1 = 10, clip2 = 11;
+    
+    // Trigger two clips
+    engine_trigger_clip(engine, clip1);
+    engine_process_commands(engine);
+    engine_trigger_clip(engine, clip2);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    assert(engine->clips[clip2].state == CLIP_RECORDING);
+    
+    // Undo twice
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_EMPTY);
+    assert(engine->clips[clip2].state == CLIP_EMPTY);
+    
+    // Redo twice
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    assert(engine->clips[clip2].state == CLIP_EMPTY);
+    
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    assert(engine->clips[clip2].state == CLIP_RECORDING);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 57: Undo scene trigger
+void test_undo_scene_trigger(void) {
+    printf("Test 57: Undo scene trigger... ");
+    Engine *engine = create_test_engine();
+    
+    int scene_idx = 3;
+    
+    // Trigger scene
+    engine_trigger_scene(engine, scene_idx);
+    engine_process_commands(engine);
+    
+    // All clips in scene should be recording
+    for (int ch = 0; ch < MAX_CHANNELS; ch++) {
+        int clip_idx = CLIP_INDEX(scene_idx, ch);
+        assert(engine->clips[clip_idx].state == CLIP_RECORDING);
+    }
+    
+    // Undo: all clips should go back to empty
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    for (int ch = 0; ch < MAX_CHANNELS; ch++) {
+        int clip_idx = CLIP_INDEX(scene_idx, ch);
+        assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    }
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 58: Undo clip state cycle (empty -> recording -> looping -> stopped)
+void test_undo_clip_state_cycle(void) {
+    printf("Test 58: Undo clip state cycle... ");
+    Engine *engine = create_test_engine();
+    
+    int clip_idx = 10;
+    
+    // Cycle through all states
+    engine_trigger_clip(engine, clip_idx);  // empty -> recording
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_RECORDING);
+    
+    engine_trigger_clip(engine, clip_idx);  // recording -> looping
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_LOOPING);
+    
+    engine_trigger_clip(engine, clip_idx);  // looping -> stopped
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_STOPPED);
+    
+    // Undo three times to go back to empty
+    engine_undo_action(engine);  // stopped -> looping
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_LOOPING);
+    
+    engine_undo_action(engine);  // looping -> recording
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_RECORDING);
+    
+    engine_undo_action(engine);  // recording -> empty
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 59: Undo after new action clears redo history
+void test_undo_clears_redo_on_new_action(void) {
+    printf("Test 59: Undo after new action clears redo history... ");
+    Engine *engine = create_test_engine();
+    
+    int clip1 = 10, clip2 = 11;
+    
+    // Trigger clip1
+    engine_trigger_clip(engine, clip1);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    
+    // Undo
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_EMPTY);
+    
+    // Redo should work
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_RECORDING);
+    
+    // Undo again
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_EMPTY);
+    
+    // Now do a new action (trigger clip2)
+    engine_trigger_clip(engine, clip2);
+    engine_process_commands(engine);
+    assert(engine->clips[clip2].state == CLIP_RECORDING);
+    
+    // Redo should NOT work now (redo history cleared)
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip1].state == CLIP_EMPTY);  // Should still be empty
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 60: Undo reset clip
+void test_undo_reset_clip(void) {
+    printf("Test 60: Undo reset clip... ");
+    Engine *engine = create_test_engine();
+    
+    int clip_idx = 10;
+    
+    // Set up a looping clip with data
+    engine->clips[clip_idx].state = CLIP_LOOPING;
+    engine->clips[clip_idx].buffer_size = 100;
+    engine->clips[clip_idx].write_position = 100;
+    engine->clips[clip_idx].read_position = 50;
+    
+    // Reset the clip
+    engine_reset_clip(engine, clip_idx);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    assert(engine->clips[clip_idx].buffer_size == 0);
+    
+    // Undo: should restore clip to previous state
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_LOOPING);
+    assert(engine->clips[clip_idx].buffer_size == 100);
+    assert(engine->clips[clip_idx].write_position == 100);
+    assert(engine->clips[clip_idx].read_position == 50);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 61: Undo/redo with quantize mode change
+void test_undo_quantize_change(void) {
+    printf("Test 61: Undo quantize mode change... ");
+    Engine *engine = create_test_engine();
+    
+    assert(engine->quantize_mode == QUANTIZE_OFF);
+    
+    // Change quantize mode
+    engine_set_quantize_mode(engine, QUANTIZE_BEAT);
+    engine_process_commands(engine);
+    assert(engine->quantize_mode == QUANTIZE_BEAT);
+    
+    // Undo: should go back to OFF
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->quantize_mode == QUANTIZE_OFF);
+    
+    // Redo: should go back to BEAT
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->quantize_mode == QUANTIZE_BEAT);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 62: Undo/redo with threshold change
+void test_undo_threshold_change(void) {
+    printf("Test 62: Undo threshold change... ");
+    Engine *engine = create_test_engine();
+    
+    assert(engine->quantize_threshold == 0);
+    
+    // Change threshold
+    engine_set_quantize_threshold(engine, 1000);
+    engine_process_commands(engine);
+    assert(engine->quantize_threshold == 1000);
+    
+    // Undo: should go back to 0
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->quantize_threshold == 0);
+    
+    // Redo: should go back to 1000
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->quantize_threshold == 1000);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 63: Undo/redo with transport reset
+void test_undo_transport_reset(void) {
+    printf("Test 63: Undo transport reset... ");
+    Engine *engine = create_test_engine();
+    
+    // Set up transport state
+    engine->transport.rolling = true;
+    engine->transport.clock_count = 100;
+    engine->transport.beat_position = 2;
+    engine->transport.bar_position = 5;
+    engine->transport.sample_position = 10000;
+    
+    // Reset transport
+    engine_reset_transport(engine);
+    engine_process_commands(engine);
+    assert(engine->transport.rolling == false);
+    assert(engine->transport.clock_count == 0);
+    
+    // Undo: should restore transport state
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->transport.rolling == true);
+    assert(engine->transport.clock_count == 100);
+    assert(engine->transport.beat_position == 2);
+    assert(engine->transport.bar_position == 5);
+    assert(engine->transport.sample_position == 10000);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
+// Test 64: Undo/redo with paste operation
+void test_undo_paste(void) {
+    printf("Test 64: Undo paste operation... ");
+    Engine *engine = create_test_engine();
+    
+    int clip_idx = 27;
+    
+    // Simulate paste: trigger clip three times to go empty -> recording -> looping -> stopped
+    engine_trigger_clip(engine, clip_idx);
+    engine_trigger_clip(engine, clip_idx);
+    engine_trigger_clip(engine, clip_idx);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_STOPPED);
+    
+    // Undo: should go back to empty
+    engine_undo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_EMPTY);
+    
+    // Redo: should go back to stopped
+    engine_redo_action(engine);
+    engine_process_commands(engine);
+    assert(engine->clips[clip_idx].state == CLIP_STOPPED);
+    
+    printf("PASSED\n");
+    destroy_test_engine(engine);
+}
+
 int main(void) {
     printf("Running TUI tests...\n\n");
     
@@ -1266,6 +1639,18 @@ int main(void) {
     test_visual_yank_then_escape();
     test_multiple_marks();
     test_remark_existing_mark();
+    test_undo_single_trigger();
+    test_undo_multiple_triggers();
+    test_redo_single_undo();
+    test_redo_multiple_undos();
+    test_undo_scene_trigger();
+    test_undo_clip_state_cycle();
+    test_undo_clears_redo_on_new_action();
+    test_undo_reset_clip();
+    test_undo_quantize_change();
+    test_undo_threshold_change();
+    test_undo_transport_reset();
+    test_undo_paste();
     
     printf("\nAll TUI tests passed!\n");
     return 0;

tui.c

@@ -735,6 +735,20 @@ void tui_run(Engine *engine) {
                 break;
             }
                 
+            case 'u': {
+                // Undo
+                engine_undo_action(engine);
+                engine_process_commands(engine);
+                break;
+            }
+                
+            case 18: {  // Ctrl+R (18 = 0x12)
+                // Redo
+                engine_redo_action(engine);
+                engine_process_commands(engine);
+                break;
+            }
+                
             case 27:  // Escape key
             case 'Q':
                 return;