Prevent unvalidated registrations from reserving domain names indefinitely.
Give pending registrations a 48-hour validation window and clean up expired entries at startup and every 60 minutes. Emit CustomDomainValidationExpired for each deletion and preserve registrations referenced by services.
Reject validation after expiry and prevent concurrent validation from recreating deleted registrations. Normalize domain names with the shared parser before registration.
Migrate existing pending registrations to receive a fresh 48-hour validation window.
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