The Favorites count is re-read 300 ms after a star changes. A reload
inside that window started the read on the leaving page, which WebKit
fails ("access control checks") and reports as a page error. After
beforeunload, the workspace clears that timer, aborts count reads in
flight and defers new ones, as well as a finished restore's reload. A
page that stays reads them on its next input or when it becomes visible,
as the legacy admin page does.