Function get_curated_group_from_xname_hostlist 

pub async fn get_curated_group_from_xname_hostlist(
    infra: &InfraContext<'_>,
    auth_token: &str,
    xname_vec: &[String],
) -> Result<HashMap<String, Vec<String>>, Error>

Group the supplied xnames by their parent HSM group.

Fetches the HSM groups the caller can access, then for each group returns the intersection of its membership with xname_vec. Groups whose intersection is empty are omitted, so the returned map contains only groups that actually contribute at least one matching node.