A new custom domain needs a TXT record proving your team owns it

A custom domain now serves your app only once we find its _ib-verify TXT record, listed with its other records on the app's Domains page. Pointing a CNAME at us is no longer enough on its own, so a hostname another team removed but left pointing here can't be picked up by someone else. Domains already live keep working with nothing to add; one still pending needs the record before it goes live, and a domain never proven within 7 days is let go.