instrument: snap live params onto a fresh voice, roll a live drag back on capture loss, serialize the seqlock's two writers

src/core/instrument/engine/voice.cpp

@@ -197,13 +197,24 @@ void Voice::start(int note, int velocity, const SampleData& sample, bool declick
 
 void Voice::applyLive(const instrument::engine::LiveValues& live, bool snap) {
     // Gate's amplitude envelope is the AHDSR; Trigger's fade shape is anchored to a play span
-    // resolved at note-on and is not a live control, so it is deliberately untouched here.
-    if (playMode_ == PlayMode::Gate) env_.applyLive(live.adsr);
-    pitchEnv_.applyLive(live.pitchEnvAttackFrames, live.pitchEnvDecayFrames,
-                        live.pitchEnvPeakSemitones);
+    // resolved at note-on and travels by reload instead (deck_groups.h names why).
+    //
+    // A fresh note and a sounding one take DIFFERENT envelope entry points, never one with a
+    // flag: a voice that has rendered nothing has no phase to hold and nothing to be
+    // continuous with, and the mid-stage rule misreads its stage-0 position (envelopes.h).
+    if (snap) {
+        if (playMode_ == PlayMode::Gate) env_.snapLive(live.adsr);
+        pitchEnv_.snapLive(live.pitchEnvAttackFrames, live.pitchEnvDecayFrames,
+                           live.pitchEnvPeakSemitones);
+    } else {
+        if (playMode_ == PlayMode::Gate) env_.applyLive(live.adsr);
+        pitchEnv_.applyLive(live.pitchEnvAttackFrames, live.pitchEnvDecayFrames,
+                            live.pitchEnvPeakSemitones);
+    }
     if (!filterOn_) return;  // filter enable is a discrete toggle: it travels by reload
 
-    filterEnv_.applyLive(live.filterEnv);
+    if (snap) filterEnv_.snapLive(live.filterEnv);
+    else filterEnv_.applyLive(live.filterEnv);
     filterCutoffNorm_ = static_cast<double>(live.filterSettings.cutoffNorm);
     filterKeyTrack_ = live.filterKeyTrack;
     filterSettings_.morphLaw = live.filterSettings.morphLaw;