Function is_win32_hidden_sentinel 

fn is_win32_hidden_sentinel(r: &Rect) -> bool

Phase B.9.1 — Win32 sentinel positions for “this window is hidden.” CEF parks new windows here briefly between create and first paint; same value family (SW_HIDE analog used by ITaskbarList::DeleteTab removed windows). We suppress drift emission for these but DO trigger corrective move (the user shouldn’t see the sentinel).