unsupported_digest_algorithm· code· HTTP 422· scope bothThe digest suite prefix in a typed digest value (e.g. sha256:<hex>, cbor.sha256:<hex>) is not an active row of artifacts/registry/digest-suite-registry.json supported by the receiver (unknown id, unregistered tuple, or reserved suite) on a critical field. See zh/conformance/encoding.md §3.1-§3.2. Dual-registered (also a reason_code): all four algorithm-agility fail-closed errors (unsupported_digest_algorithm / unsupported_signature_alg / unsupported_hpke_suite / unsupported_ciphersuite) appear in both `codes` (top-level service error) and `reason_codes` (per-item sub-reason); see zh/conformance/schema-registry.md §1.1.1.