Service both VST3 parameter channels, and promote pitch key-track and Trigger length so all 44 ids issue

The SDK's own single-component sample drains inputParameterChanges in
process() and implements setParamNormalized; automation was reading the
GUI channel alone. The audio thread now patches a block it solely owns.

src/core/instrument/engine/voice.h

@@ -45,6 +45,9 @@ inline double pitchRatio(int note, int rootNote) {
 // ((note-root)*1.0 is exact in IEEE-754 for an integer-valued double, feeding the same
 // std::pow call); 0.0 means every key plays the root pitch; 2.0 doubles the tracking rate.
 // At the root note the offset is 0 regardless of keyTrack.
+// "Not supplied" for Voice::start's two snapshot-defaulted note-on latches; see start().
+inline constexpr double kLatchFromSnapshot = -1.0;
+
 inline double keyTrackedRatio(int note, int rootNote, double keyTrack) {
     const double semis = static_cast<double>(note - rootNote) * keyTrack;
     return std::pow(2.0, semis / 12.0);
@@ -124,8 +127,16 @@ public:
     // to consult gets exactly that; VoiceEngine::startVoice is what resolves the real value —
     // sample.play.playRate is NOT read here, because the published block outranks the snapshot's
     // possibly-stale copy of it.
+    //
+    // `keyTrack` and `lengthFraction` are the other two members of stretchRate's note-on-latched
+    // class and arrive the same way, for the same structural reason. Negative = not supplied,
+    // which reads the snapshot's own value (sample.keyTrack, effectiveLengthFraction(play)) —
+    // both are non-negative by domain, so the sentinel can never collide with a real one.
+    // VoiceEngine::startVoice always supplies them, resolved from the published block when there
+    // is one; the sentinel is for a caller that has no block to consult.
     void start(int note, int velocity, const SampleData& sample, bool declickTakeover = false,
-               double stretchRate = 1.0);
+               double stretchRate = 1.0, double keyTrack = kLatchFromSnapshot,
+               double lengthFraction = kLatchFromSnapshot);
 
     // Mono legato takeover: re-pitch this active voice to `note` without touching the
     // amplitude envelope, read position, or shifter state — pitch moves, no re-attack. Both
@@ -201,7 +212,7 @@ private:
     // shifter's transpose. Cold: note-on, legato retune, and a live block, never per frame.
     void recomputeBaseRatio() {
         if (sample_ == nullptr) return;
-        baseRatio_ = keyTrackedRatio(note_, sample_->rootNote, sample_->keyTrack) *
+        baseRatio_ = keyTrackedRatio(note_, sample_->rootNote, keyTrack_) *
                      velPitchRatio_ * pitchOffsetRatio_ * rateRatio_;
     }
 
@@ -710,6 +721,10 @@ private:
     double velPitchRatio_ = 1.0; // the velocity->pitch factor alone; retune re-applies it
     double pitchOffsetRatio_ = 1.0;  // the Pitch knob's factor — LIVE, re-applied by applyLive
     double rateRatio_ = 1.0;     // Rate's factor of the read increment; start() owns when it is 1
+    // Key-track, LATCHED at note-on beside the rate. Held here rather than re-read off the
+    // snapshot so a legato retune and a live block re-apply the note's own value; a published
+    // move reaches the next note only.
+    double keyTrack_ = kKeyTrackDefault;
     // Whether this note is ACTUALLY taking the Preserve read — a Preserve voice whose shifters
     // were never sized falls back to the varispeed one, and the two domains differ. Latched at
     // note-on beside rateRatio_, which start() resolves from the same predicate.