fix(tests): rework testNoteOffReleasesNewestSameNote to actually prove newest-first release; add single-frame-loop test; add two comments in sampler_core.cpp

src/vst/sampler_core.cpp

@@ -199,6 +199,9 @@ AudioSample Voice::renderFrame() {
     if (loopUsable && i1 >= loop.end) {
         i1 = loop.start;  // seamless wrap for the interpolation partner.
     }
+    // i0 is always in [0, frameCount) after the early-out above; the guard is purely
+    // defensive. i1 (the interpolation partner) can exceed frameCount when no loop
+    // wraps it — only that partner actually needs the clamp.
     const double s0 = (i0 >= 0 && i0 < frameCount) ? static_cast<double>(pcm[i0]) : 0.0;
     const double s1 = (i1 >= 0 && i1 < frameCount) ? static_cast<double>(pcm[i1]) : 0.0;
     const double interp = s0 + (s1 - s0) * frac;
@@ -288,7 +291,7 @@ void VoiceEngine::noteOff(int note) {
 
 void VoiceEngine::render(std::vector<AudioSample>& out, std::size_t frameCount) {
     const std::size_t base = out.size();
-    out.resize(base + frameCount, 0.0f);
+    out.resize(base + frameCount, 0.0f);  // S4: caller must pre-reserve — no allocation allowed under the VST3 process callback.
     for (Voice& voice : voices_) {
         if (!voice.active()) continue;
         for (std::size_t f = 0; f < frameCount; ++f) {