fix(pitch_shift): ratio-scale splice fade so +24st up-shifts never read stale data; normalize SOLA correlation by candidate energy; tests bracket 4x/0.5x + unity/latency asserts

src/vst/pitch_shift.h

@@ -105,10 +105,15 @@ private:
     double posA_ = 0.0;              // active read tap (advances at the shift ratio)
     double posB_ = 0.0;              // outgoing tap during a splice crossfade
     bool fading_ = false;            // a splice crossfade is in flight
-    std::int64_t fadePos_ = 0;       // crossfade progress, [0, fadeFrames_)
-    std::int64_t fadeFrames_ = 0;    // crossfade length (window_/4)
+    std::int64_t fadePos_ = 0;       // crossfade progress, [0, fadeLen_)
+    std::int64_t fadeFrames_ = 0;    // NOMINAL crossfade length (window_/4)
+    std::int64_t fadeLen_ = 0;       // LIVE crossfade length for the in-flight splice —
+                                     // ratio-scaled at splice time so an up-shift's outgoing
+                                     // tap can never drain into the writer mid-fade
     std::int64_t maxLag_ = 0;        // correlation search half-range (window_/4)
-    std::int64_t corrFrames_ = 0;    // correlation dot-product length (window_/4, capped)
+    std::int64_t corrFrames_ = 0;    // correlation segment length (dLow_-1, capped at 512, so
+                                     // the reference read forward from the tap stays behind
+                                     // the writer BY CONSTRUCTION at an up-splice)
     std::int64_t dLow_ = 0;          // splice trigger: active-tap delay below this (up-shift)
     std::int64_t dHigh_ = 0;         // splice trigger: active-tap delay above this (down-shift)
     double ratio_ = 1.0;             // current shift ratio (>0)