Result of a cheap structural probe of an .fcr file’s recipient list.
Not a security claim.probe_recipient_mode performs no KDF, no
private-key operation, no credential prompt, no header-MAC verification,
and no payload decryption. A positive result is not evidence that the file
is authentic, decryptable, untampered, or well-formed beyond the structural
shape required to classify it. Use only for UI / routing hints.
Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.