Function is_loopback_host 

pub fn is_loopback_host(host: &str) -> bool

Whether a hostname resolves to this machine.

*.localhost counts. RFC 6761 reserves the whole subtree for loopback, and minting gives every agent a subdomain, so a development zone is agents.localhost and every agent under it lands here. This answers what a deployment has around it — no public DNS, no operator’s repository, no relay that can reach it — not what scheme it speaks.