Bounded digest failures without body, field, or algorithm input bytes.

• :mismatch - a computed checksum differs from the field.
• :unsupported_algorithm - no SHA-256/SHA-512 checksum can be checked, or a computation's algorithm list is not a nonempty unique list of "sha-256" and "sha-512".
• :uncomputed_algorithm - a stream did not hash a supported algorithm present in the field.
• :conflicting_digest - a supported algorithm repeats across combined field occurrences, including identical checksums.
• :invalid_digest_length - a known algorithm's checksum has the wrong size.
• :invalid_preference - a preference weight is outside 0..10.
• :body_unavailable - the body is streaming, unavailable, or consumed; this distinguishes missing bytes from retained empty content.
• :representation_required - a representation check lacks explicit complete representation bytes.
• :invalid_field - a preference selector other than the two RFC 9530 preference field names.
• :invalid_body, :invalid_message, :invalid_kind, :invalid_chunk, :invalid_state, and :invalid_options - invalid caller values. A :max_bytes above 16 MiB on RequestSeal.Digest.compute/3 or RequestSeal.Digest.check/3 returns :invalid_options.
• :limit - content bytes exceed the :max_bytes bound.

Structured Fields errors retain their own bounded reason vocabulary (RequestSeal.StructuredFields.Error); for example, an invalid Message given to RequestSeal.Digest.check_stream/3 or RequestSeal.Digest.preferences/3 returns that module's :invalid_message. No failure returns partial integrity facts.