Deleting a custom domain released its name while services still pointed
at it, leaving them on a namespace the account no longer held.
Deletion now refuses with 412 when a service in the same account uses the
domain or a subdomain, including disabled ones. Service writes revalidate
authorization inside their transaction and hold a shared lock on the
matching registrations, so a delete racing a create cannot strand either.
The dependency lookup is account-scoped: registrations are unique by name,
so another account can hold team.example.com under example.com and its
services are authorized by its own registration.
Require validated custom domains when creating or updating reverse proxy services.
Propagate validation errors during updates and return HTTP 409 for duplicate domain claims.
Add regression tests for domain validation, ownership, and service creation and updates.
Maycon Santos