Function mark_fetched 

pub async fn mark_fetched(
    conn: &mut PgConnection,
    course_code: &str,
    started_at: DateTime<Utc>,
    could_claim_mail: bool,
    listed_person_count: i32,
    duration_ms: i32,
) -> ModelResult<Option<DateTime<Utc>>>

Records an enrolment list that arrived, or Suotar saying it holds no realisation of the code, and clears the failure streak. started_at is what mark_attempted returned for the request, and could_claim_mail whether the list was free to claim linking mail; only such a fetch serves the waiting people’s rungs and presses. Returns when the code was fetched before this.