@petrichor it's a bit fiddly but it's doable, @f0x does it for pixie.town. Iirc it's essentially about forwarding webfinger requests from the top level domain to the relevant subdomain running mastodon
@dumpsterqueer @petrichor oh wow it's actually documented now too: https://docs.joinmastodon.org/admin/config/#basic WEB_DOMAIN entry