I feel like the RPC protocol (minus a good text representation) that LSP needs is ONC RPC. It's ancient, to be sure, but it is stupid simple to implement either

I feel like the RPC protocol (minus a good text representation) that LSP needs is ONC RPC. It's ancient, to be sure, but it is stupid simple to implement either with a ton of boilerplate or with a compiler to generate the structs and serializers/deserializers for you.