Type-enforce the waveform overlay contract, narrow waveformLanes to LaneSplit, fix laneCount/cache/path-fallback bugs

src/shell/instrument/editor_input_waveform.cpp

@@ -2,8 +2,7 @@
 // start/loop marker, and resolving both drags live against the pure inverse maps
 // (envelope_edit, waveform_view). Windows-only.
 //
-// Hit-test and drag both resolve against WaveformSurface::overlay — the same full-band rect
-// the overlays draw into — so a grab in the lower stereo lane reaches them.
+// Overlay contract: see waveform_view.h's WaveformSurface.
 
 #include "shell/instrument/reasampler_editor.h"
 
@@ -27,7 +26,7 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
     const std::vector<AudioSample>& pcm = monoPcmFor(selectedId_);
     const std::int64_t frames = static_cast<std::int64_t>(pcm.size());
     if (frames <= 0) return false;
-    const Rect overlay = waveformOverlayArea(fl.bands.waveform);
+    const OverlayArea overlay = waveformOverlayArea(fl.bands.waveform);
 
     // Envelope nodes first (they sit on top of the markers), then the wave markers.
     const double rate = liveSampleRate();
@@ -64,7 +63,7 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
 }
 
 void ReaSamplerEditor::dragWaveform(const FaceLayout& fl, int x, int y) {
-    const Rect overlay = waveformOverlayArea(fl.bands.waveform);
+    const OverlayArea overlay = waveformOverlayArea(fl.bands.waveform);
     const int dx = x - dragStartX_;
 
     if (drag_ == DragKind::kEnvNode) {