This is someone's rust port of the new "cap'n web" protocol Kenton just released, which he's calling a spiritual sibling to cap'n proto (which he also built). This might be AI slop but this info is all in the OP, come on man!

I know all that already and none of it goes against what I said, so why the antagonistic tone?

I do think that Kenton shares some of the blame by making their new JSON-based schemaless RPC system so similarly named to their old binary schema-based serialization format... I don't get the reasoning there. But that doesn't change what I said.