Function receiver 

pub(crate) fn receiver<T>(work: impl FnOnce() -> T) -> T

work (what a reminder records, then its export) as a session of its own when none is open here: up first, so that a process ended in its midst leaves the others in doubt rather than sure; down after, then the sync app asked to carry it (share::nudge_carriers): the lowered entry goes up, not the raised one.