Fix stuck audition notes under rapid / chord tapping (v0.8.1)

The synth/SF2 audition note-off matched a voice purely by pitch, and isActive
stays true through a voice's release tail. So tapping a key, then immediately
holding it again, landed the note-off on the still-releasing first voice (a
no-op) and left the held one stuck, needing a MIDI panic. Two fingers on one
key hit the same trap.

Give voices an isGated flag (held = ADSR not in release/idle) and make
auditionSlotOff / liveNoteOff release a gated voice of that pitch in preference
to one already ringing out. Add SynthVoiceGateTest covering the gate/release
distinction and the exact stuck-note scenario.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/build.gradle.kts

@@ -22,8 +22,8 @@ android {
         // (android.media.midi) and AAudio low-latency audio we rely on.
         minSdk = 26
         targetSdk = 34
-        versionCode = 23
-        versionName = "0.8.0"
+        versionCode = 24
+        versionName = "0.8.1"
 
         // We provide our own instrumentation runner if/when tests are added.
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"

app/src/main/java/space/rcmd/android/sizzle/audio/AudioEngine.kt

@@ -527,7 +527,10 @@ class AudioEngine(
     }
 
     fun liveNoteOff(pitch: Int) {
-        liveVoices.firstOrNull { it.isActive && it.pitch == pitch }?.noteOff()
+        // Prefer a held (gated) voice over one already releasing, so a fast retrigger
+        // of the same pitch never leaves the held voice stuck (see [auditionSlotOff]).
+        (liveVoices.firstOrNull { it.pitch == pitch && it.isGated }
+            ?: liveVoices.firstOrNull { it.isActive && it.pitch == pitch })?.noteOff()
     }
 
     // ------------------------------------------------------------- render loop
@@ -1075,10 +1078,15 @@ class AudioEngine(
         v.noteOn(midi, 110, patchForSlot(slot, project?.tempoBpm ?: 120f))
     }
 
-    /** Release an auditioned note (matches both synth and sample audition pools). */
+    /** Release an auditioned note (matches both synth and sample audition pools).
+     *  Releases a *held* (gated) voice of this pitch in preference to one that's already
+     *  ringing out its release tail — otherwise rapid re-tapping / chord-tapping the same
+     *  key lands the note-off on the releasing voice and leaves the held one stuck. */
     fun auditionSlotOff(midi: Int) {
-        liveVoices.firstOrNull { it.isActive && it.pitch == midi }?.noteOff()
-        auditionSampleVoices.firstOrNull { it.isActive && it.pitch == midi }?.noteOff()
+        (liveVoices.firstOrNull { it.pitch == midi && it.isGated }
+            ?: liveVoices.firstOrNull { it.isActive && it.pitch == midi })?.noteOff()
+        (auditionSampleVoices.firstOrNull { it.pitch == midi && it.isGated }
+            ?: auditionSampleVoices.firstOrNull { it.isActive && it.pitch == midi })?.noteOff()
     }
 
     // ---------------------------------------------- live mix-bus audition (MIDI piano)

app/src/main/java/space/rcmd/android/sizzle/audio/SampleVoice.kt

@@ -64,6 +64,10 @@ class SampleVoice(private val engineSampleRate: Int) {
     private val declickCoeff = exp(-1f / (engineSampleRate * 0.003f)) // ~3 ms decay
 
     val isActive: Boolean get() = sample != null
+    /** Note is still *held* (not in its release stage). A voice ringing out its
+     *  release tail is still [isActive]; distinguishing the two lets a note-off
+     *  target the held voice instead of one already releasing — see [SynthVoice.isGated]. */
+    val isGated: Boolean get() = sample != null && phase != Phase.RELEASE
 
     /**
      * @param root MIDI note at which the sample plays at its natural pitch.

app/src/main/java/space/rcmd/android/sizzle/audio/SynthVoice.kt

@@ -55,6 +55,11 @@ class SynthVoice(private val sampleRate: Int) {
     private val filtEnv = Adsr()
 
     val isActive: Boolean get() = ampEnv.active
+    /** Gate is still open (attack/decay/sustain) — the note is *held*. A voice in its
+     *  release tail is still [isActive] but no longer gated; distinguishing the two
+     *  lets a note-off target the held voice instead of one that's already ringing
+     *  out (which otherwise leaves the held note stuck under rapid re-tapping). */
+    val isGated: Boolean get() = ampEnv.gateOpen
 
     /** Start (or steal-and-restart) this voice with the given [patch]. */
     fun noteOn(midi: Int, velocity: Int, patch: SynthPatch) {
@@ -254,6 +259,8 @@ class SynthVoice(private val sampleRate: Int) {
         private var level = 0f
         private var a = 0.01f; private var d = 0.1f; private var s = 0.7f; private var r = 0.2f
         val active: Boolean get() = stage != 0
+        /** Attack/decay/sustain — i.e. gate on, not yet released (stage 4) or idle (0). */
+        val gateOpen: Boolean get() = stage in 1..3
 
         fun gateOn(aa: Float, dd: Float, ss: Float, rr: Float) {
             a = aa.coerceAtLeast(0.0005f); d = dd; s = ss.coerceIn(0f, 1f); r = rr

app/src/test/java/space/rcmd/android/sizzle/audio/SynthVoiceGateTest.kt

@@ -0,0 +1,73 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package space.rcmd.android.sizzle.audio
+
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Locks the gate-vs-release distinction the audition note-off relies on. A voice in
+ * its release tail must report [SynthVoice.isActive] == true (still sounding) but
+ * [SynthVoice.isGated] == false, so a note-off preferring a gated voice never lands
+ * on a releasing one — the fix for stuck notes under rapid / chord tapping.
+ */
+class SynthVoiceGateTest {
+
+    private val sr = 48_000
+
+    @Test fun heldNoteIsGated() {
+        val v = SynthVoice(sr)
+        v.noteOn(60, 100, SynthPatch.DEFAULT)
+        assertTrue("a freshly triggered note is gated", v.isGated)
+        assertTrue(v.isActive)
+        // Advance well past the attack/decay into sustain — still held.
+        repeat(sr / 2) { v.render() }
+        assertTrue("a sustaining note is still gated", v.isGated)
+        assertTrue(v.isActive)
+    }
+
+    @Test fun releasingNoteIsActiveButNotGated() {
+        val v = SynthVoice(sr)
+        v.noteOn(60, 100, SynthPatch.DEFAULT)
+        repeat(sr / 4) { v.render() } // reach sustain
+        v.noteOff()
+        // One sample into the release: still audible, but no longer gated.
+        v.render()
+        assertTrue("a releasing voice is still active (audible tail)", v.isActive)
+        assertFalse("a releasing voice is no longer gated", v.isGated)
+    }
+
+    @Test fun releaseReachesSilence() {
+        val v = SynthVoice(sr)
+        v.noteOn(60, 100, SynthPatch.DEFAULT)
+        repeat(sr / 4) { v.render() }
+        v.noteOff()
+        // DEFAULT release is 0.2 s; render a full second to be safe.
+        repeat(sr) { v.render() }
+        assertFalse("the voice frees itself after the release completes", v.isActive)
+        assertFalse(v.isGated)
+    }
+
+    /** The stuck-note scenario at the voice level: a releasing voice and a held voice
+     *  of the same pitch coexist; selecting the gated one for note-off leaves no held
+     *  voice behind (whereas picking the first *active* match would strand it). */
+    @Test fun gatedPreferenceReleasesTheHeldVoice() {
+        val releasing = SynthVoice(sr)
+        val held = SynthVoice(sr)
+        releasing.noteOn(60, 100, SynthPatch.DEFAULT)
+        repeat(sr / 4) { releasing.render() }
+        releasing.noteOff()
+        releasing.render() // now active-but-not-gated
+        held.noteOn(60, 100, SynthPatch.DEFAULT) // same pitch, gated
+
+        val pool = listOf(releasing, held)
+        // Mirror auditionSlotOff's selection: prefer a gated voice of this pitch.
+        val target = pool.firstOrNull { it.pitch == 60 && it.isGated }
+            ?: pool.firstOrNull { it.isActive && it.pitch == 60 }
+        target?.noteOff()
+
+        assertFalse("the held voice received the note-off and is releasing", held.isGated)
+    }
+}