fix(web): prevent browser context menu over task menus (#1627)

ui/flutter/lib/shared/widgets/browser_context_menu_region.dart

@@ -0,0 +1,81 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
+import 'browser_context_menu_region_stub.dart'
+    if (dart.library.js_interop) 'browser_context_menu_region_web.dart'
+    as platform;
+
+/// Keeps the browser menu out of an application's context-menu region on Web.
+///
+/// Captured themes carry the policy into shadcn's menu and submenu overlays.
+/// Overlay regions defer to their children so a full-screen positioning layer
+/// does not suppress the browser menu over the rest of the page.
+class BrowserContextMenuRegion extends StatelessWidget {
+  const BrowserContextMenuRegion({super.key, required this.child});
+
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    if (!kIsWeb) return child;
+    return _ContextMenuTheme(
+      child: _ContextMenuRegion(behavior: HitTestBehavior.translucent, child: child),
+    );
+  }
+}
+
+class _ContextMenuTheme extends InheritedTheme {
+  const _ContextMenuTheme({required super.child});
+
+  @override
+  Widget wrap(BuildContext context, Widget child) {
+    return _ContextMenuTheme(child: _ContextMenuRegion(child: child));
+  }
+
+  @override
+  bool updateShouldNotify(_ContextMenuTheme oldWidget) => false;
+}
+
+class _ContextMenuRegion extends SingleChildRenderObjectWidget {
+  const _ContextMenuRegion({this.behavior = HitTestBehavior.deferToChild, required super.child});
+
+  final HitTestBehavior behavior;
+
+  @override
+  RenderObject createRenderObject(BuildContext context) {
+    return _RenderContextMenuRegion(View.of(context).viewId, behavior);
+  }
+
+  @override
+  void updateRenderObject(BuildContext context, _RenderContextMenuRegion renderObject) {
+    renderObject
+      ..viewId = View.of(context).viewId
+      ..behavior = behavior;
+  }
+}
+
+class _RenderContextMenuRegion extends RenderProxyBoxWithHitTestBehavior {
+  _RenderContextMenuRegion(this._viewId, HitTestBehavior behavior) : super(behavior: behavior);
+
+  int _viewId;
+
+  set viewId(int value) {
+    if (value == _viewId) return;
+    if (attached) platform.unregisterRegion(this, _viewId);
+    _viewId = value;
+    if (attached) platform.registerRegion(this, _viewId);
+  }
+
+  @override
+  void attach(PipelineOwner owner) {
+    super.attach(owner);
+    platform.registerRegion(this, _viewId);
+  }
+
+  @override
+  void detach() {
+    platform.unregisterRegion(this, _viewId);
+    super.detach();
+  }
+}