Function deliver_break 

pub fn deliver_break<R: Runtime>(
    app: &AppHandle<R>,
    current_break: &Arc<Mutex<Option<BreakEvent>>>,
    event: BreakEvent,
    delivery: BreakDelivery,
    placement: MonitorPlacement,
    windowed_fraction: f64,
)

Surface a break through whichever channel the active settings ask for: a system notification or the overlay (full-screen or windowed). Notification delivery short-circuits the overlay path entirely.

event carries the break content (kind, duration, hints, …); the delivery and placement decide how and where it surfaces.