Release held VST3 notes on reset instead of discarding them

Fixes #441

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/vst3-host/src/plugin.rs

@@ -213,8 +213,14 @@ impl Plugin for Vst3Plugin {
     }
 
     fn reset(&mut self) {
-        self.notes.clear();
+        // Keep pending releases and release whatever is still held, so the processor's voices stop
+        // on the next block instead of sounding on while the host forgets them.
+        self.notes.retain(|e| matches!(e, NoteEvent::Off { .. }));
+        for e in &mut self.notes {
+            e.set_time(0);
+        }
         self.controls.clear();
+        self.all_notes_off();
         self.held = [false; 128];
     }
 

crates/vst3-host/tests/fixture_e2e.rs

@@ -144,6 +144,29 @@ fn synth_plays_notes_at_their_offsets() {
     assert!(mono[0].iter().all(|&x| (x - 1.0).abs() < 1e-6), "the note is still held");
 }
 
+#[test]
+fn reset_after_all_notes_off_still_releases_held_voices() {
+    let mut p = soundcraft_vst3_host::create(&id_of("Fixture Synth")).unwrap();
+    p.prepare(48_000.0, 64, 2);
+    p.note_on(0, 60, 127);
+    let mut io = vec![vec![0.0f32; 64], vec![0.0f32; 64]];
+    p.process(&mut io, 64);
+    assert!((io[0][63] - 1.0).abs() < 1e-6, "the note sounds");
+    // Mixer::reset calls these two in a row on an instrument (stop / seek).
+    p.all_notes_off();
+    p.reset();
+    let mut io = vec![vec![9.0f32; 64], vec![9.0f32; 64]];
+    p.process(&mut io, 64);
+    assert!(io[0].iter().all(|x| x.abs() < 1e-6), "voice still sounding after reset: {}", io[0][63]);
+    // A reset alone also releases what the host still holds.
+    p.note_on(0, 61, 127);
+    p.process(&mut io, 64);
+    assert!((io[0][63] - 1.0).abs() < 1e-6);
+    p.reset();
+    p.process(&mut io, 64);
+    assert!(io[0].iter().all(|x| x.abs() < 1e-6), "voice still sounding after reset: {}", io[0][63]);
+}
+
 #[test]
 fn many_instances_create_and_drop_cleanly() {
     let (g, s) = (id_of("Fixture Gain"), id_of("Fixture Synth"));