MCP is going stateless, and the upgrade breaks in both directions

tldr: MCP revision 2026-07-28 removes protocol-level sessions, the initialize handshake, the GET stream endpoint, and SSE resumability, and starts a twelve-month deprecation clock on Roots, Sampling, and Logging. Every request now carries its own protocol version and capabilities. A client speaking the new revision cannot talk to a server speaking the old one, and the reverse fails too, so supporting both is the only migration path.