Digest Fields (Content-Digest and Repr-Digest)
RFC 9530 lets a server publish a cryptographic hash of what it sent, so a client can detect corruption in transit. Worth shipping on APIs, file downloads, and machine-readable endpoints; browsers ignore it.
RFC 9110 — HTTP Semantics §8.1 (Representation Data), §6.4 (Content)
IANA — Hash Algorithms for HTTP Digest Fields