An app bar's overflow menu is two separate <x-menu> instances trading places as the width crosses 600px, each display: none where the other shows. Resizing away from a menu's trigger left its popover in an open state forever, anchored to a wrapper nobody could see or reach anymore. A ResizeObserver on the trigger now closes the menu once it has no box left to render (plan step 36, navigation group). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9