Fix shared element state across component instances

crates/layout/tests/resize_handle.rs

@@ -151,6 +151,28 @@ fn moves_without_a_drag_report_nothing() {
     assert!(deltas.borrow().is_empty());
 }
 
+/// The button may be released outside the window, where no MouseUp is
+/// delivered — the drag must end when a move reports no pressed button.
+#[test]
+fn releasing_outside_the_window_ends_the_drag() {
+    let (_cx, deltas, _resets, mut visual) = handle_window(Axis::Horizontal, false);
+    let start = handle_center(&mut visual);
+
+    visual.simulate_mouse_down(start, MouseButton::Left, Modifiers::default());
+    visual.simulate_event(MouseMoveEvent {
+        position: point(start.x + px(30.), start.y),
+        pressed_button: None,
+        modifiers: Modifiers::default(),
+    });
+    visual.simulate_event(MouseMoveEvent {
+        position: point(start.x + px(60.), start.y),
+        pressed_button: None,
+        modifiers: Modifiers::default(),
+    });
+
+    assert!(deltas.borrow().is_empty(), "the drag outlived its button");
+}
+
 #[test]
 fn arrow_keys_move_the_seam_when_focused() {
     let (_cx, deltas, _resets, mut visual) = handle_window(Axis::Horizontal, false);