Function apply_hwnd_position_changed 

pub fn apply_hwnd_position_changed(
    state: &mut State,
    hwnd: u64,
    new_rect: Rect,
) -> Vec<Event>

Phase B.9.1 — handle Command::ReportHwndPositionChanged. Compares the new rect against state.monitors; emits OffMonitor drift if it doesn’t intersect any monitor. Suppressed when state.monitors is empty (we don’t yet know the topology — first ReportMonitorTopologyChanged will reconcile every label’s last_rect against fresh monitors).