Clear stale hover on capture-loss and Alt-delete; derive gutter test via chromeRects

src/shell/instrument/editor_input.cpp

@@ -82,7 +82,10 @@ void ReaSamplerEditor::onMouseUp(int x, int y) {
     // hover_ is deliberately not re-resolved during a drag (see resolveHover's caller), so it
     // still names wherever the drag started. Re-resolve now against the release position, for
     // every drag kind — otherwise the next paint latches a stale hover (wrong note name/tooltip,
-    // wrong control outline) until the next WM_MOUSEMOVE.
+    // wrong control outline) until the next WM_MOUSEMOVE. This resolve runs before the release
+    // branches below can delete or relocate the hovered element; a future branch that does so
+    // must clear hover_ itself afterwards (as the curve drag-off delete does below) rather than
+    // rely on this resolve, which reflects pre-mutation state.
     resolveHover(x, y);
     // A scrollbar drag is transient UI (no parameter change), and the processor-side knobs
     // (the preview-velocity -2 sentinel, voice count, master gain) are per-instance settings

src/shell/instrument/editor_input_curve.cpp

@@ -47,7 +47,10 @@ void ReaSamplerEditor::handleCurveMouseDown(const Rect& r, int x, int y) {
     // Modifier-click (Alt) deletes an interior node — a discrete, final edit committed at once
     // (deletePoint refuses the two endpoints, so an Alt-click on them is a safe no-op).
     if (idx >= 0 && (GetKeyState(VK_MENU) & 0x8000) != 0) {
-        if (params_.velocityCurve.deletePoint(static_cast<std::size_t>(idx))) commitAndReload();
+        if (params_.velocityCurve.deletePoint(static_cast<std::size_t>(idx))) {
+            hover_ = HoverTarget{};  // a stale kCurveNode index would light a shifted node
+            commitAndReload();
+        }
         return;
     }
 

src/shell/instrument/editor_platform.cpp

@@ -231,6 +231,10 @@ LRESULT CALLBACK ReaSamplerEditor::wndProc(HWND hwnd, UINT msg, WPARAM wParam,
                     self->drag_ = DragKind::kNone;
                     self->dragParamId_ = -1;
                     self->curvePointIndex_ = -1;  // curve-node drag state (peer reset)
+                    // No cursor position is available here to re-resolve hover (unlike
+                    // onMouseUp's release coordinates), so clear rather than leave it naming
+                    // wherever the drag started.
+                    self->hover_ = HoverTarget{};
                     self->invalidate();
                 }
             }