Returns "io.modelcontextprotocol/clientCapabilities", the request _meta key for the client's capabilities. Every request must carry it.

Returns "io.modelcontextprotocol/clientInfo", the optional request _meta key for the client's implementation name and version.

Returns "io.modelcontextprotocol/protocolVersion", the request _meta key for the protocol version. Every request must carry it.

Returns "io.modelcontextprotocol/serverInfo", the result _meta key under which the server sends the runtime's server_info with every result.