fix(vst): master-gain per-sample ramp (no zipper/click); voice-count commits once on release; minor review items

src/vst/master_gain.h

@@ -33,8 +33,10 @@ double masterGainMaxLinear();
 // [kMasterGainMinDb, kMasterGainMaxDb]. norm is clamped to [0,1]. Pure.
 double masterGainDbFromNorm(double norm);
 
-// Inverse taper: dB -> normalized [0,1]. -infinity (or any dB at/below kMasterGainMinDb)
-// maps to the bottom of the finite sweep (0 for -inf, else the clamped floor); +24 -> 1. Pure.
+// Inverse taper: dB -> normalized [0,1]. -infinity (or any dB at or below kMasterGainMinDb,
+// including below-floor values like -80 dB) maps to norm 0 (the -inf bottom detent) — the
+// finite sweep only covers the range above kMasterGainMinDb; everything at or below it collapses
+// to the same true-zero bottom. +24 -> 1. Pure.
 double masterGainNormFromDb(double db);
 
 // Knob taper composed with dB->ratio: normalized [0,1] -> LINEAR gain. norm 0 -> exactly
@@ -42,8 +44,10 @@ double masterGainNormFromDb(double db);
 double masterGainLinearFromNorm(double norm);
 
 // Inverse: LINEAR gain -> normalized [0,1]. linear <= 0 -> 0 (the -inf bottom); a linear at
-// or below the kMasterGainMinDb floor also reads ~0+ (the taper's finite bottom); unity ->
-// ~0.714; masterGainMaxLinear() -> 1. Out-of-range/non-finite input clamps. Pure.
+// or below the kMasterGainMinDb floor (e.g. 0.001 = -60 dB, or anything below) also maps to 0
+// — the floor IS the -inf detent; values between true-zero and the floor cannot be represented
+// on the knob and collapse to the bottom. unity -> ~0.714; masterGainMaxLinear() -> 1.
+// Out-of-range/non-finite input clamps. Pure.
 double masterGainNormFromLinear(double linear);
 
 // The knob's hover/drag value label for a normalized value: "-inf" at the bottom, else a