Constant HIDDEN_SINCE_OPEN_GRACE_MS 

const HIDDEN_SINCE_OPEN_GRACE_MS: u64 = 500;

Placement grace window. CEF creates top-level windows hidden, runs SetWindowPos to place them, then shows them. The intermediate WM_HIDE events arrive before WM_FOREGROUND, which would otherwise look like HiddenSinceOpen drift on every fresh window. Hides occurring within this window of the host’s ReportWindowOpened are part of normal placement and don’t count.