Send MCP message via streamable HTTP

Send a JSON-RPC 2.0 message to the MCP server over streamable HTTP. This is an alternative transport to SSE for MCP client connections. Supports all MCP protocol operations including tool invocations (scrape_docs, search_docs, fetch_url, list_libraries, find_version, list_jobs, get_job_info, cancel_job, remove_docs, refresh_version) and resource access.