Fix cross-rate Preserve splices, re-stamp on host-rate change, name the rate refusal

The splice crossfade now counts output frames and stops before the ring's far end (this also fixes a lap at matched rate). The search strides by the rate ratio. The editor takes its time base from its own decode. Same-rate output is pinned to hashes from before the change.

src/shell/instrument/editor_input_waveform.cpp

@@ -42,7 +42,7 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
     // (overlayEnvInert flips the staged one inert exactly when its envelope is in Spline mode),
     // so at most one of the two hit-tests below is ever live for the same click — both feed the
     // SAME arbitration slot below rather than either one getting its own check-order return.
-    const double rate = liveSampleRate();
+    const double rate = selectedSourceRate();
     const bool nodesLive =
         overlayEnv_ != OverlayEnv::kNone && !overlayEnvInert(overlayEnv_, gates);
     NodeHit envNodeHit;
@@ -245,7 +245,7 @@ void ReaSamplerEditor::dragWaveform(const FaceLayout& fl, int x, int y) {
         // set. The StageEnvelope was snapshotted at grab (dragStartEnv_) so the delta is
         // absolute.
         const std::int64_t frames = dragSampleFrames_;
-        const double rate = liveSampleRate();
+        const double rate = selectedSourceRate();
         if (frames <= 0 || rate <= 0.0) return;
         const double totalSeconds = static_cast<double>(frames) / rate;
         const DragModifiers mods = dragModifiers();