Default-deny, or an unlisted cluster accepts anything.

Binary Authorization blocks any image lacking required attestations from a trusted attestor.

policy.yaml

defaultAdmissionRule:
  evaluationMode: ALWAYS_DENY
clusterAdmissionRules:
  meridian-prod:
    requireAttestationsBy: [vulnerability-scan, qa-signoff]

Any cluster with NO explicit rule falls through to the default. A permissive default left "temporarily" during rollout defeats the entire control for every cluster not yet locked down.