fix(pitch_shift): re-anchor fadePos_ on freeze so gNew is continuous at the freeze frame; guard left cast; add step-detector + loop-never-freezes regression

tests/test_sampler_core.cpp

@@ -1318,6 +1318,16 @@ static void testPreserveGateStereoLoopComposes() {
     }
     CHECK(maxL > 0.05);
     CHECK(maxR > 0.02);  // R present (half amplitude), distinct from L -> stereo preserved
+    // Loop-never-freezes regression: the Preserve voice must NOT spuriously freeze when the
+    // read tap hits the sample end and the loop wraps it back. A spuriously frozen voice
+    // stops writing to the ring and the looped tail would go silent past the sample end.
+    // Check a block far past the sample end (sample = 400 frames; window = 512; well past
+    // any single-pass tail region) to catch any wrap-before-exhaustion ordering error.
+    double maxLFar = 0.0;
+    for (std::size_t i = 1800; i < 2000; ++i) {
+        if (std::fabs(left[i]) > maxLFar) maxLFar = std::fabs(left[i]);
+    }
+    CHECK(maxLFar > 0.05);  // still alive at frame 1800 (4.5× the 400-frame sample length)
 }
 
 // --- Preserve voice cap: a Preserve note-on past the cap is dropped; Varispeed unaffected. ---