fix(voice): CC 120 hard-stops voices (incl. Trigger); Mono sizes voices_ to 1; comments corrected

CC 120 -> allSoundsOff/hardStop (immediate silence, stops Trigger one-shots); CC 123 -> allNotesOff/releaseAll (release, unchanged). Mono VoiceEngine sizes voices_ to 1 structurally. Legato same-note re-press edge documented. Three new tests.

tests/test_sampler_core.cpp

@@ -1793,6 +1793,65 @@ static void testPreviewCardReleaseAll() {
     CHECK(!card.active());
 }
 
+// CC 120 (allSoundsOff) hard-stops a ringing TRIGGER one-shot that would otherwise play to
+// its bounded playEnd (minutes on a full-length capture). This is the primary repro: allNotesOff
+// (CC 123) is a NO-OP on a Trigger voice — only allSoundsOff provides the actual hard stop.
+static void testAllSoundsOffStopsTriggerOneShot() {
+    // A Trigger sample with a very long play length (all-1 DC, flat velocity). After noteOn the
+    // voice is active and ringing; allSoundsOff must silence it immediately.
+    SampleData s = dcLevelSample(200000, 1.0f, 60);
+    s.play.playMode = PlayMode::Trigger;
+    s.play.trigger.lengthFraction = 1.0;  // full length — would ring for 200000 frames
+    Keymap km = Keymap::singleSampleChromatic(std::move(s));
+    VoiceEngine eng(1, km);
+    eng.noteOn(60, 127);
+    CHECK(eng.activeVoiceCount() == 1);
+    // CC 123 (release) must be a NO-OP on a Trigger voice — the one-shot plays through.
+    eng.allNotesOff();
+    CHECK(eng.activeVoiceCount() == 1);   // still ringing (Trigger ignores release)
+    std::vector<AudioSample> out;
+    eng.render(out, 1);
+    CHECK(out[0] > 0.5f);                // still sounding
+    // CC 120 (hard-stop) must silence it instantly.
+    eng.allSoundsOff();
+    CHECK(eng.activeVoiceCount() == 0);  // immediately idle
+    out.clear();
+    eng.render(out, 1);
+    CHECK(approx(out[0], 0.0, 1e-9));    // silent
+}
+
+// CC 123 (allNotesOff) still releases Gate voices — the existing release behavior is unchanged.
+static void testAllNotesOffStillReleasesGateVoices() {
+    SampleData s = dcLevelSample(200000, 1.0f, 60);
+    // Default Gate mode, instant release (releaseFrames 0).
+    Keymap km = Keymap::singleSampleChromatic(std::move(s));
+    VoiceEngine eng(4, km);
+    eng.noteOn(60, 127);
+    eng.noteOn(62, 127);
+    CHECK(eng.activeVoiceCount() == 2);
+    eng.allNotesOff();
+    std::vector<AudioSample> out;
+    eng.render(out, 1);
+    CHECK(approx(out[0], 0.0, 1e-9));    // Gate with 0-release: instant silence
+    CHECK(eng.activeVoiceCount() == 0);
+}
+
+// MONO LEGATO same-note re-press (one-held-note edge case): with only that note on the
+// stack, heldCount_ after the re-push is 1 (not >= 2), so it falls through to re-attack
+// rather than retune. This is the correct fresh-phrase behavior documented in the comment.
+static void testMonoLegatoSameNoteRepressReattacks() {
+    SampleData s = rampSample(200000, 60);
+    Keymap km = Keymap::singleSampleChromatic(std::move(s));
+    VoiceEngine eng(2, km, 0, 0, VoiceMode::Mono, MonoTrigger::Legato);
+    eng.noteOn(60, 127);                        // first press; read starts at 0
+    std::vector<AudioSample> out;
+    eng.render(out, 10);                        // advance the read head to ~10
+    // Re-press the SAME note while it is the only held note: heldCount_ after removeHeld+push = 1
+    // -> does NOT satisfy heldCount_ >= 2 -> re-attack (not a legato retune).
+    eng.noteOn(60, 127);
+    CHECK(approx(probeFrame(eng), 0.0, 1e-4));  // read RESTARTED at 0 (re-attack, not retune)
+}
+
 // GREEN: out-of-range notes are rejected at BOTH mono entry points. The held stack stores
 // uint8, so an unguarded off for note 256 (== 0 mod 256) would alias-evict held note 0 —
 // losing its fallback. Note-ons out of [0,127] are a defined no-play.
@@ -1970,6 +2029,9 @@ int main() {
     testAllNotesOffReleasesPolyVoices();
     testAllNotesOffClearsMonoHeldStack();
     testPreviewCardReleaseAll();
+    testAllSoundsOffStopsTriggerOneShot();
+    testAllNotesOffStillReleasesGateVoices();
+    testMonoLegatoSameNoteRepressReattacks();
     testMonoOutOfRangeNotesRejected();
     testVoiceCountBoundsPolyphony();
     testPreviewCardIsolatedFromPool();