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

src/core/instrument/ui/envelope_edit.cpp

@@ -63,7 +63,8 @@ bool nodeInMode(EnvNode n, EnvMode m) {
 
 }  // namespace
 
-NodeHit nodeAtPoint(const AmpEnvelope& env, const Rect& area, double totalSeconds, int x, int y) {
+NodeHit nodeAtPoint(const AmpEnvelope& env, const OverlayArea& area, double totalSeconds, int x,
+                    int y) {
     const std::vector<EnvVertex> poly = buildEnvelopePolyline(env, area, totalSeconds);
     // Nearest draggable, mode-matching node within the pick radius wins (Chebyshev distance);
     // ties go to the earlier draw-order node. Only matters for Trigger's zero-fade-out
@@ -81,16 +82,17 @@ NodeHit nodeAtPoint(const AmpEnvelope& env, const Rect& area, double totalSecond
     return best;
 }
 
-AmpEnvelope resolveNodeDrag(const AmpEnvelope& grabEnv, EnvNode node, const Rect& area,
+AmpEnvelope resolveNodeDrag(const AmpEnvelope& grabEnv, EnvNode node, const OverlayArea& area,
                             double totalSeconds, const EnvClampBounds& bounds,
                             int dxPixels, int dyPixels) {
     AmpEnvelope out = grabEnv;
     if (!isDraggable(node) || !nodeInMode(node, grabEnv.mode)) return out;
 
-    const double secPerPx = secondsPerPixel(area, totalSeconds);
+    const Rect& rect = area.rect;
+    const double secPerPx = secondsPerPixel(rect, totalSeconds);
     if (secPerPx <= 0.0) return out;  // degenerate area / duration — no motion
     const double dSec = static_cast<double>(dxPixels) * secPerPx;
-    const double gateDSec = static_cast<double>(dxPixels) * gateSecondsPerPixel(area);
+    const double gateDSec = static_cast<double>(dxPixels) * gateSecondsPerPixel(rect);
 
     switch (node) {
         // Gate: each cumulative-time node edits its own segment duration. Non-negative durations
@@ -106,7 +108,7 @@ AmpEnvelope resolveNodeDrag(const AmpEnvelope& grabEnv, EnvNode node, const Rect
         case EnvNode::DecayEnd: {
             // X sets decay time, Y sets sustain level (drag down = higher y = lower level).
             out.decaySeconds = std::clamp(grabEnv.decaySeconds + gateDSec, 0.0, bounds.maxDecaySeconds);
-            const double lvlPerPx = levelPerPixel(area);
+            const double lvlPerPx = levelPerPixel(rect);
             const double dLevel = -static_cast<double>(dyPixels) * lvlPerPx;
             out.sustainLevel = std::clamp(grabEnv.sustainLevel + dLevel, 0.0, 1.0);
             break;