fix: add ring buffer data before overflow trigger in test

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

test_engine.c

@@ -328,6 +328,12 @@ void test_buffer_overflow(void) {
     // Fill buffer to max
     state->clips[0].write_position = MAX_BUFFER_SIZE;
     
+    // Write data into the ring buffer so the reducer can copy it
+    for (size_t i = 0; i < MAX_BUFFER_SIZE; i++) {
+        state->record_buffer[0][i] = (float)i;
+    }
+    atomic_store(&state->record_write_pos[0], MAX_BUFFER_SIZE);
+    
     // Trigger should stop recording and start looping
     reducer(state, action);
     assert(state->clips[0].state == CLIP_LOOPING);