Function init_follower_node 

pub async fn init_follower_node<P>(
    genesis: Genesis,
    params: FollowerParams,
    metrics: Box<dyn Metrics>,
    persistence: P,
    l1_params: L1Params,
    sink: impl DecideSink + 'static,
) -> Result<FollowerHandle<P>>
where
    P: SequencerPersistence + MembershipPersistence,
    Arc<P>: Storage<SeqTypes>,

The follow loop is running when this returns; FollowerContext::new takes over stopping it.