Function recompute_preconditions 

pub async fn recompute_preconditions(
    conn: &mut PgConnection,
    scope: &RegistrationScope,
    limit: i64,
) -> ModelResult<i64>

Applies at most limit moves to the scoped rows and returns how many moved.

A row a worker claimed between the snapshot and the write is left where it is: its state is that phase’s to own now, and the next iteration decides again from whatever it committed. Writing anyway could put an in-flight import back into a state a second import claims.

A row that would start resolving without ever having been checked starts its enrolment check schedule instead: nobody has enrolled at the moment they complete, so it waits in no_usable_enrolment for the first rung of its group’s ladder unless that rung is due already. A row waiting there is left to resolve-enrolments, which checks it where it stands.