instrument: fix AHD node-tracking/tie-break/live-latch defects and close staged-envelope-curve test gaps

tests/test_live_delivery.cpp

@@ -474,6 +474,62 @@ static void testEveryEnvelopeStageTimeAndLevelMovesTheSoundingNote() {
              s.play.pitchEnv.peakSemitones = 12.0;
          },
          [](LiveValues& v) { v.pitchEnv.peakSemitones = 0.0; }, -1},
+        // A small hold that finishes the envelope well inside the render window (Hold ends at
+        // frame ~5090, comfortably short of the window) vs. a live move that opens the hold out
+        // near the whole span: with the fraction alone unmoved, the boundary the two renders
+        // cross (or don't) inside the observed tail is what makes this audible, not a level
+        // change — Hold's own output is flat regardless of exactly where inside it pos_ sits.
+        {"pitch env hold fraction",
+         [](SampleData& s) {
+             s.play.pitchEnv.enabled = true;
+             s.play.pitchEnv.peakSemitones = 12.0;
+             s.play.pitchEnv.shape.attackFrames = 100;
+             s.play.pitchEnv.shape.decayFrames = 100;
+             s.play.pitchEnv.shape.holdFraction = 0.05;
+         },
+         [](LiveValues& v) { v.pitchEnv.shape.holdFraction = 1.0; }, -1},
+
+        // The Trigger AHDs — Voice::applyLive's ampAhd_/filterAhd_ branches, otherwise
+        // unexercised by this table (every case above is Gate/AdsrEnvelope).
+        {"trigger amp attack (AHD)",
+         [](SampleData& s) {
+             s.play.playMode = PlayMode::Trigger;
+             s.play.trigger.lengthFraction = 1.0;
+             s.play.trigAhd.attackFrames = 48000;
+         },
+         [](LiveValues& v) { v.ampAhd.attackFrames = 4000; }, -1},
+        {"trigger filter attack (AHD)",
+         [](SampleData& s) {
+             s.play.playMode = PlayMode::Trigger;
+             s.play.trigger.lengthFraction = 1.0;
+             filterSweep(s);
+             s.play.filter.trigEnv.attackFrames = 48000;
+         },
+         [](LiveValues& v) { v.filterAhd.attackFrames = 4000; }, -1},
+
+        // One curve exponent per envelope (amp/pitch/filter), reusing each envelope's own
+        // attack/decay rig above so only the mutated field differs.
+        {"amp attack curve",
+         [](SampleData& s) { s.play.adsr.attackFrames = 48000; },
+         [](LiveValues& v) { v.adsr.attackCurve = 5.0; }, -1},
+        {"amp release curve",
+         [](SampleData& s) { s.play.adsr.releaseFrames = 48000; },
+         [](LiveValues& v) { v.adsr.releaseCurve = 5.0; }, 2},
+        {"pitch env attack curve",
+         [](SampleData& s) {
+             s.play.pitchEnv.enabled = true;
+             s.play.pitchEnv.shape.attackFrames = 48000;
+             s.play.pitchEnv.shape.decayFrames = 48000;
+             s.play.pitchEnv.peakSemitones = 12.0;
+         },
+         [](LiveValues& v) { v.pitchEnv.shape.attackCurve = 5.0; }, -1},
+        {"filter env decay curve",
+         [](SampleData& s) {
+             filterSweep(s);
+             s.play.filter.env.decayFrames = 48000;
+             s.play.filter.env.sustainLevel = 0.0;
+         },
+         [](LiveValues& v) { v.filterEnv.decayCurve = 5.0; }, -1},
     };
     for (const Case& c : cases) {
         assertLiveFieldMovesTheSoundingNote(c.name, c.rig, c.mutate, c.noteOffBlock);