Public endpoint: Lookup domain ID by subdomain. Returns only the domain_id, to minimise data exposure. Resolution does not filter on hosting status; see _lookup_domain_id_for_host for how a (legacy) duplicate canonical host is decided.

alias_redirect_host is the canonical desk host when this host is a configured alias (agents.json spec §8): the edge worker permanent-redirects to it instead of resolving content. An alias WINS over resolution — the operator has explicitly said this host is not canonical — so a host that is both listed as an alias and shaped like a desk host redirects.

Hosts under the Free plan's base resolve through _lookup_free_host alone — first, so neither an alias nor a canonical match can claim one.