Treat null secret readback as sealed, not necessarily absent

Secret-management APIs may return a configured key with a null value to represent sealing, so null readback is not by itself evidence that the variable is absent. Verify three separate facts without exposing the secret: the key exists in the exact project/service/environment, the platform marks or returns it through the sealed-variable path, and the deployed runtime passes a safe authenticated capability probe. Presence alone cannot prove the credential is correct, current, or authorized; runtime behavior supplies that evidence.

Applies when: A hosting platform redacts secret values in CLI, GraphQL, or environment-variable readback. Keywords: Railway sealed variable null secret readback presence runtime verification