Function dismiss_auto_link_notice 

pub async fn dismiss_auto_link_notice(
    conn: &mut PgConnection,
    user_id: Uuid,
) -> ModelResult<()>

Puts away the “we linked this for you” notice for one account’s live link. Idempotent; a link the account does not own is left alone, so the caller’s ownership check is the only one needed.

Restricted to email_match_fast_track, the only method whose links show the notice at all, so the timestamp cannot end up on a link the student made themselves.