instrument: latch the note done at the read-head run-off, fit the migrated fades, and lift the curve dial and overlay selection into pure modules

src/core/instrument/engine/voice.cpp

@@ -90,8 +90,16 @@ void Voice::start(int note, int velocity, const SampleData& sample, bool declick
     }
 
     // The pitch AHD's Hold fraction is taken against the whole playable span, so its three
-    // stages lay 1:1 over the waveform from the start point.
-    pitchEnv_.configure(postStart, p.pitchEnv);
+    // stages lay 1:1 over the waveform from the start point. postStart is a SOURCE-frame count
+    // and this envelope counts OUTPUT frames (envelopes.h), so Varispeed — which consumes
+    // baseRatio_ source frames per output frame — needs the span converted, or a transposed
+    // note's envelope outruns (or outlives) the note it shapes. Preserve reads at the source
+    // rate, so its two domains already coincide.
+    const double pitchSpan =
+        (pitchEngine_ == PitchEngine::Preserve || !(baseRatio_ > 0.0))
+            ? static_cast<double>(postStart)
+            : static_cast<double>(postStart) / baseRatio_;
+    pitchEnv_.configure(static_cast<std::int64_t>(pitchSpan + 0.5), p.pitchEnv);
     pitchEnv_.noteOn();
 
     // A restart lands every live glide back on the new note's own values, at a step derived