PopupMutex guarded CurrentPopupOpts against a popup being created on a
worker goroutine while the UI thread deactivated it, or reset it on a
repo switch. Now that popup and menu creation is bounced onto the UI
thread, every access to CurrentPopupOpts — create, deactivate, and the
reset-on-switch (which already runs on the UI thread) — happens on the
one goroutine, so the mutex protects nothing.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>