Function is_on_any_monitor 

pub fn is_on_any_monitor(
    pos: BubblePosition,
    window_width: i32,
    window_height: i32,
    monitors: &[MonitorBounds],
) -> bool

true iff the bubble (top-left at pos, size (w, h)) is at least partially visible on any of the supplied monitors. Used after a display unplug to decide whether the persisted position is still usable or should fall back to default_position.

A position counts as visible if the window’s rectangle intersects the monitor’s rectangle (any pixel overlap — not requiring full containment, since the user may have intentionally placed the bubble half-off-screen and we shouldn’t reset their choice).