Read-only precheck: true if absent or equal; false for a different existing pin.
After successful manifest validation, atomically insert if absent or compare with the existing pin. Return false on mismatch, including a concurrent change since check(). A successful precheck is never a reservation or authorization.
Call only after independently confirming a publisher's migration. Never call from an automatic retry.
Process-local pointer integrity. Use durable shared storage across workers/restarts.