One taper, one modifier law: extract param_taper, raise the stage ceiling to 10 s, and make the AHDSR schematic axis the taper itself

src/shell/instrument/editor_input_curve.cpp

@@ -47,9 +47,9 @@ void ReaSamplerEditor::handleCurveMouseDown(const Rect& r, int x, int y) {
 
     // Alt-click delete is retired (the spec's right-click supersedes it — one grammar, no
     // migration on either side): every gesture here routes through the shared resolver.
-    const bool ctrl = (GetKeyState(VK_CONTROL) & 0x8000) != 0;
-    const SplineEdit edit = resolveSplineEdit(
-        editedCurve(), box, ctrl ? SplineGesture::kControlLeft : SplineGesture::kLeft, x, y);
+    const SplineGesture gesture =
+        dragModifiers().ctrl ? SplineGesture::kControlLeft : SplineGesture::kLeft;
+    const SplineEdit edit = resolveSplineEdit(editedCurve(), box, gesture, x, y);
     if (edit.kind == SplineEditKind::kToggleHard) {
         if (editedCurve().toggleHard(static_cast<std::size_t>(edit.index))) commitAndReload();
         return;