Staggered Menu Animation cookbook example: drawer close doesn't reverse the staggered item animation

### Page URL https://docs.flutter.dev/cookbook/effects/staggered-menu-animation ### Page source https://github.com/flutter/website/blob/main/sites/docs/src/content/cookbook/effects/staggered-menu-animation.md ### Describe the problem On the Staggered Menu Animation cookbook example, the closing animation doesn't mirror the opening one. The drawer slide (`_drawerSlideController`, 150ms) closes the panel, but the internal staggered item animation (`_staggeredController` inside `_MenuState`) only ever runs `.forward()` once in `initState()` and is never reversed. `_isDrawerClosed()` checks only `_drawerSlideController.value == 0.0`. As soon as the 150ms slide finishes, this becomes true and _buildDrawer immediately swaps `Menu()` for `SizedBox()`, disposing the `Menu` widget's state entirely. Result: opening shows a polished staggered entrance (panel slides in, then items animate in one by one with stagger + elastic button). Closing just slides the whole panel away as a solid block in 150ms — none of the menu items animate out, since their controller never reverses and the widget is torn down before anything could play. ### Expected fix Lift `_staggeredController` (and its Intervals) out of `_MenuState` and into `_ExampleStaggeredAnimationsState`, passing them into `Menu` as constructor parameters (`Menu` becomes a `StatelessWidget`). This keeps the controller alive across the drawer's full open/close lifecycle instead of being recreated/disposed with the widget. In `_toggleDrawer`, sequence the close so items animate out first, then the panel slides away: ```dart void _toggleDrawer() { if (_isDrawerOpen() || _isDrawerOpening()) { _staggeredController.reverse().whenCompleteOrCancel(() { _drawerSlideController.reverse(); }); } else { _drawerSlideController.forward(); _staggeredController.forward(from: 0.0); } } ``` Update `_isDrawerClosed()` to require both controllers at `0.0`: ```dart bool _isDrawerClosed() => _drawerSlideController.value == 0.0 && _staggeredController.value == 0.0; ``` This keeps Menu mounted long enough for the staggered exit animation to finish before the panel itself is removed. ### Additional context Affects the example source linked above (staggered menu animation cookbook page) Purely an animation-sequencing issue in the sample code, not platform/browser specific Happy to open a PR with the corrected main.dart — I have a working version that fixes the close animation while keeping the existing open animation intact ### I would like to fix this problem. - [x] I will try and fix this problem on docs.flutter.dev.