Function retire_due_timers 

pub fn retire_due_timers(
    timers: ResMut<'_, TimerRegistry>,
    due_out: ResMut<'_, DueTimers>,
)

Collect the timers whose deadline has passed, reschedule the repeating ones, and drop the one-shots. Host-neutral and registered once, so each active host is offered the same due list instead of the first one to run taking it.

Reschedule / remove happens BEFORE any host fires, so a handler that calls cancel_timer or set_interval on the same name sees a clean slate. Due timers are sorted by name for determinism.