fix: close review findings on the velocity-curve deck and bipolar curves

Cancels the curve-node drag whenever the popup closes so Esc mid-drag can't alias the amp curve; generalizes CurveTarget routing to one switch; fixes stale/overstated comments; clamps a pre-v12 depth fold; adds deck-inertness and filter-fold test coverage.

src/shell/instrument/editor_controls.cpp

@@ -53,7 +53,9 @@ namespace {
 // The ceiling is READ from the overlay's schematic scale rather than restated: the AHDSR
 // schematic anchors a maxed knob at the canvas edge, which only holds while the two agree.
 constexpr double kEnvTimeMaxSeconds = instrument::ui::kGateStageMaxSeconds;
-constexpr double kPitchDepthMaxSemis = 24.0;          // pitch depth throw: +/-24 st, centered
+// Pitch depth throw: +/-kVelocityPitchRangeSemitones, centered. The one throw the pitch
+// envelope's peak and the velocity->pitch curve's full scale both speak (play_params.h).
+constexpr double kPitchDepthMaxSemis = kVelocityPitchRangeSemitones;
 constexpr double kKeyTrackMax = 2.0;                 // key-track slider ceiling (0..200%)
 
 // The raw stored curve exponent for a curve-dial control id, read DIRECTLY off the field —
@@ -510,21 +512,43 @@ void ReaSamplerEditor::unpackEnvelope(OverlayEnv which, const StageEnvelope& env
     }
 }
 
-const VelocityCurve& ReaSamplerEditor::editedCurve() const {
-    switch (curvePopup_) {
+const VelocityCurve& ReaSamplerEditor::curveFor(CurveTarget target) const {
+    switch (target) {
         case CurveTarget::kPitch:  return params_.play.pitchVelocityCurve;
         case CurveTarget::kFilter: return params_.play.filter.velocityCurve;
         case CurveTarget::kAmp:
         case CurveTarget::kNone:
-            // kNone only reaches here from a paint/hover racing the close; the amp curve is a
-            // valid, harmless read rather than a branch every caller would have to repeat.
+            // kNone reads as amp — a valid, harmless choice for a target-agnostic caller (a
+            // disabled deck cell still needs SOME curve to draw). editedCurve()'s mutable
+            // overload below refuses kNone rather than relying on this fallback to protect amp.
             return params_.velocityCurve;
     }
     return params_.velocityCurve;
 }
 
+VelocityCurve& ReaSamplerEditor::curveFor(CurveTarget target) {
+    return const_cast<VelocityCurve&>(std::as_const(*this).curveFor(target));
+}
+
+const VelocityCurve& ReaSamplerEditor::editedCurve() const { return curveFor(curvePopup_); }
+
 VelocityCurve& ReaSamplerEditor::editedCurve() {
-    return const_cast<VelocityCurve&>(std::as_const(*this).editedCurve());
+    // Refuses kNone rather than aliasing amp (see curvePopup_'s declaration for why); should be
+    // unreachable now that every writer of kNone also cancels the drag, but this is the second,
+    // independent line of defense.
+    if (curvePopup_ == CurveTarget::kNone) {
+        static VelocityCurve sink = VelocityCurve::flat();
+        return sink;
+    }
+    return curveFor(curvePopup_);
+}
+
+void ReaSamplerEditor::closeCurvePopup() {
+    curvePopup_ = CurveTarget::kNone;
+    if (drag_ == DragKind::kCurveNode) {
+        drag_ = DragKind::kNone;
+        curvePointIndex_ = -1;
+    }
 }
 
 void ReaSamplerEditor::applyParamControl(int id, double value, int segment) {