Stateless servers get stable sessions; client metadata preserved

0.9.0

Minor Changes

• #4123 c8d036e Thanks @gesh! - feat(mcp): stable sessions and client metadata on stateless / multi-pod MCP servers

  On stateless servers every request became its own session and $mcp_client_name/$mcp_client_version were missing after initialize. The SDK now mints the Mcp-Session-Id response header at initialize as a token carrying the session id and client name/version; clients replay it on every request, so any pod recovers both with no server-side store. Auto-minting requires enableJsonResponse: true on StreamableHTTPServerTransport; SSE-mode servers can set the header at the HTTP layer with the new exports.

  New exports: encodeSessionId, decodeSessionId, MCP_SESSION_HEADER, SessionTokenPayload, newSessionId. (2026-07-10)