fix: close review findings on spline EGs — engine, codec, and popup/overlay UI grammar

Live pitch depth, Gate/Spline enable-rule agreement, inert kTrigLength, NaN wire guards, hard-flag-tail corruption no longer wipes the record, RT/cold spline tie-break, retired alt-click, marker-shadow fix, plus new test coverage.

src/shell/instrument/editor_input_waveform.cpp

@@ -31,17 +31,16 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
     if (frames <= 0) return false;
     const OverlayArea overlay = waveformOverlayArea(fl.bands.waveform);
 
-    // A drawn EG's own point actions come first, for the same reason the staged nodes do —
-    // they sit on top of the markers. Its ADD, which any empty-space click satisfies, is held
-    // back until after the markers below, or a spline overlay would make them unreachable.
+    // A drawn EG's contour is evaluated below, AFTER the markers: pointAtPixel's pick radius
+    // has no box check of its own, so a coincident contour node would otherwise shadow a
+    // marker's own dedicated grab rect (the loop-crossfade tab most sharply, since it is the
+    // ONLY affordance at zero crossfade) — marker reachability wins on any pixel overlap. The
+    // staged envelope-node pass just below is unaffected (its own, longer-standing ordering).
     const DeckEnableState gates = deckEnableState();
     const bool splineLive = overlayIsSpline() && overlayEnvEnabled(overlayEnv_, gates);
     const SplineGesture gesture = (GetKeyState(VK_CONTROL) & 0x8000) != 0
                                       ? SplineGesture::kControlLeft
                                       : SplineGesture::kLeft;
-    if (splineLive && splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/false)) {
-        return true;
-    }
 
     // Envelope nodes first (they sit on top of the markers), then the wave markers. With no
     // envelope overlay-active — or with its deck group's enable toggle off, which makes the
@@ -83,6 +82,11 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
         beginMarkerDrag(static_cast<WaveMarker>(hit), m, frames, x);
         return true;
     }
+    // No marker wanted the click: a drawn EG's own node grab/toggle (never add — empty space is
+    // tried last, below).
+    if (splineLive && splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/false)) {
+        return true;
+    }
     // Nothing else wanted the click: now the drawn contour may take the empty space.
     if (splineLive) return splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/true);
     return false;
@@ -92,7 +96,15 @@ bool ReaSamplerEditor::splineOverlayClick(const OverlayArea& waveArea, int x, in
                                           SplineGesture gesture, bool addOnEmptySpace) {
     const VelocityCurve::Box box = splineOverlayBox(waveArea);
     VelocityCurve& contour = splineFor(overlayEnv_);
-    const SplineEdit edit = resolveSplineEdit(contour, box, gesture, x, y);
+    SplineEdit edit = resolveSplineEdit(contour, box, gesture, x, y);
+    // resolveSplineEdit's outside-box grab/delete/toggle allowance (pointAtPixel's radius has
+    // no box check of its own) was designed for the popup's inset ring; the overlay box has NO
+    // inset (splineOverlayBox), so honoring it here would extend the grab halo 6px into the
+    // inter-band pad. kAdd already requires in-box (resolveSplineEdit's own check).
+    if (edit.kind != SplineEditKind::kNone && edit.kind != SplineEditKind::kAdd &&
+        !(x >= box.left && x < box.left + box.width && y >= box.top && y < box.top + box.height)) {
+        edit = SplineEdit{};
+    }
     if (edit.kind == SplineEditKind::kAdd && !addOnEmptySpace) return false;
     switch (edit.kind) {
         case SplineEditKind::kNone:
@@ -125,6 +137,10 @@ bool ReaSamplerEditor::splineOverlayClick(const OverlayArea& waveArea, int x, in
     drag_ = DragKind::kSplineNode;
     curvePointIndex_ = index;
     dragStartCurve_ = contour;  // AFTER the add — resolvePointDrag's delta base
+    // The release-time drag-off-delete bound (onMouseUp), matching the popup's kCurveNode use
+    // of the same field — the two spline surfaces share one drag-off grammar, not just the
+    // click grammar.
+    dragCurveRect_ = waveArea.rect;
     dragStartX_ = x;
     dragStartY_ = y;
     invalidate();  // live feedback; the commit lands on WM_LBUTTONUP