FA1: unity-Preserve bypass kills preview onset latency; drain-slot reload keeps voices ringing through curve edits; velocity path proven end-to-end

src/vst/sampler_core.h

@@ -397,7 +397,10 @@ public:
     void setStartOrder(std::uint64_t order) { startOrder_ = order; }
     bool releasing() const { return releasing_; }
     // The S16 pitch engine this voice is running (for the engine's Preserve-voice tally). Only
-    // meaningful while active().
+    // meaningful while active(). NOTE (FA1): a Preserve ZONE voice started at unity shift
+    // (note == effective root, pitch env off) is demoted to Varispeed at start() — it runs no
+    // shifter, speaks with zero onset delay, and deliberately does not count toward the
+    // Preserve cap (it costs Varispeed CPU, not shifter CPU).
     PitchEngine pitchEngine() const { return pitchEngine_; }
 
     // Pre-SIZE this voice's Preserve pitch shifters (both channels) to `windowFrames`, OFF the