Function resolve_target_nodes 

pub async fn resolve_target_nodes(
    infra: &InfraContext<'_>,
    token: &str,
    hosts_expression_opt: Option<&str>,
    group_name_arg_opt: Option<&str>,
    settings_group_name_opt: Option<&str>,
) -> Result<Vec<String>, Error>

Resolve target nodes from either a hosts expression, an explicit HSM group name, or the settings-level HSM group.

Priority order:

1. hosts_expression — parsed and validated via from_user_hosts_expression_to_xname_vec.
2. group_name_arg_opt — the group name supplied by the CLI’s --group flag (also accepted as --hsm-group); validated for access via crate::service::authorization::validate_user_group_access, then expanded to member xnames.
3. settings_group_name_opt — the group configured in cli.toml’s hsm_group; same treatment as (2).

Returns a sorted, deduplicated Vec<String> of xnames.