Function deliver_break 

pub fn deliver_break(
    app: &AppHandle,
    current_break: &Arc<Mutex<Option<BreakEvent>>>,
    delivery: BreakDelivery,
    kind: BreakKind,
    duration_secs: u64,
    enforceable: bool,
    placement: MonitorPlacement,
    manual_finish: bool,
    postpone_available: bool,
    hints: Vec<String>,
    hint_rotate_seconds: u64,
    health_intensity: f32,
)

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.