I think some of the oddities can come from looking at sha256 as a way to make variable length data fixed length. Hashing the context and message before signing

I think some of the oddities can come from looking at sha256 as a way to make variable length data fixed length. Hashing the context and message before signing has the fingerprints of starting with RSA and pivoting later to ed25519. Janky for sure but really not bad at all. HMAC is cool and all, but from a practical standpoint you can do with concatenation if the message is prefixed with length, or you are using an algo such as blake2 where the keyed mode is prepending the key and the internal state does not allow for extension attacks.