The new gateway/use-case code left surviving mutants (empty NoCoverage on the ACL
gateway status-set, plus unasserted error messages, null-guards, and the persist
call). Add stub-handler tests for SetZaakToEindstatusAsync (eindstatus resolution,
POST framing, failure paths) and assert the approve use case's messages, null
handling and SaveAsync. Local Stryker: acl 100%, domain 98.4%, event-subscriber 100%.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
