Function recheck_no_usable_enrolment_now 

pub async fn recheck_no_usable_enrolment_now(
    conn: &mut PgConnection,
    course_id: Uuid,
    user_ids: &[Uuid],
) -> ModelResult<u64>

Brings forward the recheck of rows parked for want of an enrolment, for students the study registry now lists as enrolled.

Only the clock moves: the enrolment is re-resolved by the precondition recompute rather than assumed from a roster entry.