test(engine): cover explicit WAV stems and reusable scratch directories

Address the review by clearing stale test scratch directories before setup and exercising an explicit supported WAV format through the real command, including decoded output format, frames and audio.

crates/engine/src/cmd/file/tests.rs

@@ -121,6 +121,7 @@ fn import_audio_honours_new_tracks() {
 #[test]
 fn bounce_stems_rejects_unsupported_formats_before_writing() {
     let dir = std::env::temp_dir().join(format!("sc-stems-unsupported-format-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
     std::fs::create_dir(&dir).unwrap();
     let stems = dir.join("stems");
     let mut e = Engine::default();
@@ -138,6 +139,7 @@ fn bounce_stems_rejects_unsupported_formats_before_writing() {
 #[test]
 fn bounce_stems_rejects_non_string_formats_before_writing() {
     let dir = std::env::temp_dir().join(format!("sc-stems-format-type-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
     std::fs::create_dir(&dir).unwrap();
     let mut e = Engine::default();
     e.execute("track.new", &json!({"count": 1, "name": "Tone", "format": "mono"})).unwrap();
@@ -158,6 +160,29 @@ fn bounce_stems_rejects_non_string_formats_before_writing() {
     }
 }
 
+#[test]
+fn bounce_stems_accepts_explicit_wav_format() {
+    let dir = std::env::temp_dir().join(format!("sc-stems-explicit-wav-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir(&dir).unwrap();
+    let mut e = Engine::default();
+    let wav = tone_wav(&dir, "tone.wav");
+    e.execute("file.import_audio", &json!({"path": wav})).unwrap();
+    let stems = dir.join("stems");
+    let result = e.execute("file.bounce_stems", &json!({"dir": stems, "format": "wav", "start": 0, "end": 32, "dither": false})).unwrap();
+    let files = result["files"].as_array().unwrap();
+    assert_eq!(files.len(), 1);
+    let path = std::path::Path::new(files[0].as_str().unwrap());
+    assert_eq!(path.parent(), Some(stems.as_path()));
+    assert_eq!(path.extension().and_then(|extension| extension.to_str()), Some("wav"));
+    let (info, audio) = soundcraft_audio_io::decode(&std::fs::read(path).unwrap(), None).unwrap();
+    assert_eq!(info.format, soundcraft_audio_io::FileFormat::Wav);
+    assert_eq!(audio.frames(), 32);
+    assert_eq!(audio.num_channels(), e.session().main_format().channels());
+    assert!(audio.channels.iter().flatten().any(|sample| sample.abs() > 0.01));
+    std::fs::remove_dir_all(&dir).unwrap();
+}
+
 #[test]
 fn bounce_refuses_formats_it_cannot_write() {
     let mut e = Engine::default();