Function rebuild_health_record 

pub(crate) fn rebuild_health_record<T>(
    then: impl FnOnce() -> T,
) -> Result<T, String>

The doses’ record read again from every computer’s records at the next exchange, this computer forgetting it held it, and then (the record set aside) done before any exchange can run: one lost or broken here, started again empty, takes nothing out elsewhere. One step, under the window’s exchanges (BUSY) and the exchanges’ lock: an exchange between the two filled the record again, which then went aside, and the next mark took every other mark out on every device (review of 15 October 2026, P1). Waits for an exchange running. Returns what then gave, or what went wrong.