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.

tests/test_live_params.cpp

@@ -41,7 +41,9 @@ static void testFoldCarriesEveryContinuousControl() {
     p.pitchEnv.shape = AhdParams{7, 9, 0.4, 1.5, 0.75};
     p.pitchEnv.peakSemitones = -3.5;
 
-    const LiveValues v = foldLive(p);
+    // Distinct from filter.keyTrack below on purpose: the two are different controls and a fold
+    // that crossed them would pass under a shared value.
+    const LiveValues v = foldLive(p, /*keyTrack=*/0.8);
     CHECK(v.adsr.attackFrames == 11);
     CHECK(v.adsr.holdFrames == 22);
     CHECK(v.adsr.decayFrames == 33);
@@ -72,6 +74,21 @@ static void testFoldCarriesEveryContinuousControl() {
     CHECK(v.pitchEnv.shape.attackCurve == 1.5);
     CHECK(v.pitchEnv.shape.decayCurve == 0.75);
     CHECK(v.pitchEnv.peakSemitones == -3.5);
+    CHECK(v.keyTrack == 0.8);
+    // Spline-folded on the way in, so the block carries what the voice will actually play.
+    CHECK(!v.splineActive);
+    CHECK(v.lengthFraction == p.trigger.lengthFraction);
+}
+
+// The fold, not the voice, is where a drawn contour pins the Trigger span — so the block a
+// note-on latches already carries the folded value.
+static void testADrawnEnvelopePinsTheFoldedTriggerLength() {
+    PlayParams p;
+    p.trigger.lengthFraction = 0.25;
+    p.ampSpline.mode = EnvMode::Spline;
+    const LiveValues v = foldLive(p, kKeyTrackDefault);
+    CHECK(v.splineActive);
+    CHECK(v.lengthFraction == 1.0);
 }
 
 static void testUnpublishedBlockReadsAsNothing() {
@@ -170,6 +187,7 @@ static void testRampStepIsRateDerived() {
 
 int main() {
     testFoldCarriesEveryContinuousControl();
+    testADrawnEnvelopePinsTheFoldedTriggerLength();
     testUnpublishedBlockReadsAsNothing();
     testConcurrentReaderNeverSeesAHalfAppliedEdit();
     testRampTerminatesExactlyOnTheTarget();