Function schedule_next_attempt 

pub async fn schedule_next_attempt(
    conn: &mut PgConnection,
    id: Uuid,
    next_attempt_at: DateTime<Utc>,
) -> ModelResult<()>

Defers when the pipeline may next claim this row; the delay is the caller’s policy.

Deliberately leaves first_failed_at alone: a state that waits on a human defers too, and anchoring the retry window here would expire it.