Keep clip gain when AudioSuite inverts or duplicates.

Both processes rendered a unity-gain file and then cleared the clip's gain and envelope, so the result was quieter than the clip the user heard. Invert and Duplicate now leave that gain on the new clip. Processes that bake a new level still write a unity-gain clip.

crates/engine/src/cmd/audiosuite.rs

@@ -107,8 +107,12 @@ fn process(e: &mut Engine, p: &Value) -> Result<Value> {
         nc.name = new_name;
         nc.content = ClipContent::Audio { source: src, offset: 0 };
         nc.length = i64::try_from(frames).unwrap_or(nc.length);
-        nc.gain_db = 0.0;
-        nc.gain_env.clear();
+        // Invert and Duplicate are phase/copy operations. The clip's gain stays a clip gain,
+        // the same way its fades stay editable. Other processes bake a new file at unity gain.
+        if !matches!(name.as_str(), "invert" | "duplicate") {
+            nc.gain_db = 0.0;
+            nc.gain_env.clear();
+        }
         if let Some(pl) = s.track_mut(track).and_then(|t| t.playlist_mut()) {
             pl.clips.retain(|c| c.id != id);
         }
@@ -122,3 +126,43 @@ fn short(n: &str) -> String {
     let s: String = n.split('_').map(|w| w.chars().take(4).collect::<String>()).collect::<Vec<_>>().join("");
     s.chars().take(8).collect()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use soundcraft_audio_io::AudioBuffer;
+    use soundcraft_model::{ChannelFormat, Session, TrackKind};
+
+    fn gained_clip() -> (crate::Engine, soundcraft_model::ClipId) {
+        let mut s = Session::default();
+        let t = s.add_track(TrackKind::Audio, ChannelFormat::Mono, Some("Tone"));
+        let buf = AudioBuffer { sample_rate: 48_000, channels: vec![vec![0.5; 64]] };
+        let src = crate::io::add_source(&mut s, "tone", buf, None, FileFormat::Wav);
+        let id = s.new_clip_id();
+        let mut c = Clip::audio(id, "tone", src, 0, 0, 64);
+        c.gain_db = -6.0;
+        c.gain_env = vec![(0, 0.0), (32, -12.0)];
+        crate::edit::place_clip(&mut s, t, c);
+        s.edit.selected_clips = vec![id];
+        (crate::Engine::new(s), id)
+    }
+
+    #[test]
+    fn invert_and_duplicate_keep_clip_gain() {
+        let (mut e, id) = gained_clip();
+        e.execute("audiosuite.process", &json!({"process": "invert", "clips": [id.0]})).unwrap();
+        let c = e.session().tracks[0].clips()[0].clone();
+        assert!((c.gain_db + 6.0).abs() < 1e-6, "{}", c.gain_db);
+        assert_eq!(c.gain_env, vec![(0, 0.0), (32, -12.0)]);
+        let sample = e.session().pool.get(c.source().unwrap()).unwrap().buffer.channels[0][0];
+        assert!((sample + 0.5).abs() < 1e-3, "invert flips the file and leaves the gain on the clip, got {sample}");
+
+        let (mut e, id) = gained_clip();
+        e.execute("audiosuite.process", &json!({"process": "duplicate", "clips": [id.0]})).unwrap();
+        let c = e.session().tracks[0].clips()[0].clone();
+        assert!((c.gain_db + 6.0).abs() < 1e-6, "{}", c.gain_db);
+        assert_eq!(c.gain_env, vec![(0, 0.0), (32, -12.0)]);
+        let sample = e.session().pool.get(c.source().unwrap()).unwrap().buffer.channels[0][0];
+        assert!((sample - 0.5).abs() < 1e-3, "duplicate keeps the file level and the clip gain, got {sample}");
+    }
+}