Function locate_holder 

pub async fn locate_holder(
    store: Option<Arc<LeaseStore>>,
    uid: &str,
    own_boot_id: &str,
) -> Option<HolderEndpoint>

Find the other instance on this host that runs uid: the lease holder (its channel’s live srv, from the shared registry) or — for an instance that takes no lease — the compat probe’s hit. None when nobody else runs it, or the holder’s srv can’t be found.