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Title: [v2] Server registry + per-connection state; ServerRunner consumes Server[L] directly by maxisbey · Pull Request #2562 · modelcontextprotocol/python-sdk · GitHub

Open Graph Title: [v2] Server registry + per-connection state; ServerRunner consumes Server[L] directly by maxisbey · Pull Request #2562 · modelcontextprotocol/python-sdk

X Title: [v2] Server registry + per-connection state; ServerRunner consumes Server[L] directly by maxisbey · Pull Request #2562 · modelcontextprotocol/python-sdk

Description: PR5 of the V2 server-side refactor (Transport → Dispatcher → ServerRunner → Server registry). Stacked on #PR4 (maxisbey/v2-server-runner). Status: WIP — chunks A+B landed, chunk C (additive new-path entry points) in progress. Opening as draft so the registry/typing changes are reviewable while the rest lands. Motivation and Context ServerRunner (PR4) needs to consume the lowlevel Server as a typed handler registry rather than via the old _handle_request callback path. This PR reshapes Server so the runner can read (params_type, handler) entries directly, and adds the per-connection scaffolding (state, exit_stack, session_id, headers) that the new Context exposes. The Server generics were settled at Server[LifespanResultT] only — no transport generic, no connection-state generic. A transport generic makes Server invariant in a way that breaks bare def deploy(server: Server) plumbing helpers; the connection-state generic doesn't earn its place when stateless is the default deployment. Both remain additive later via PEP 696 trailing defaults if demand appears. The transport-layer types (Dispatcher[TT_co], DispatchContext[TT], BaseContext[TT]) keep their generic; the server layer consumes base TransportContext. What's in here so far HandlerEntry[L] frozen dataclass replaces bare callables in the registry; public add_request_handler / add_notification_handler; zero-arg capabilities() (notification_options/experimental_capabilities are now ctor kwargs) ServerRunner reads Server[L] directly — the PR4 ServerRegistry Protocol scaffold is gone Connection.session_id, Connection.state: dict[str, Any], Connection.exit_stack: AsyncExitStack (unwound shielded by ServerRunner.run() after the dispatcher closes — handlers/middleware register per-connection teardown with stdlib enter_async_context/push_async_callback) TransportContext.headers: Mapping[str, str] | None on the base; ctx.session_id / ctx.headers convenience properties on Context JSONRPCDispatcher coerces string response/progress IDs to int for correlation (matches BaseSession and the TS SDK) Still to come in this PR Additive only — nothing in the existing Server.run() / _handle_* / ServerSession path is touched. OutboundMiddleware on JSONRPCDispatcher + otel_outbound_middleware (span + W3C _meta inject on send_raw_request, mirroring BaseSession.send_request) stdio.serve(server) + StdioTransportContext — new-path stdio entry for lowlevel users Compat properties on lowlevel Context (.lifespan_context/.session proxy) so the high-level mcpserver.Context works on either backend — temporary parity scaffolding MCPServerNext sibling class routing through ServerRunner for the parametrized e2e parity suite (next PR) How Has This Been Tested? tests/server/test_runner.py end-to-end over DirectDispatcher; new tests for state persistence, exit_stack unwound on close/error, session_id/headers round-trip. tests/shared/test_jsonrpc_dispatcher.py for the ID coercion. 100% coverage on touched files. Breaking Changes None yet. This PR is additive; the old runtime path is untouched. The eventual breaking changes (delete _handle_*/ServerSession/BaseSession) are deferred until the parity suite proves equivalence. Types of changes Bug fix (non-breaking change which fixes an issue) New feature (non-breaking change which adds functionality) Breaking change (fix or feature that would cause existing functionality to change) Documentation update Checklist I have read the MCP Documentation My code follows the repository's style guidelines New and existing tests pass locally I have added appropriate error handling I have added or updated documentation as needed AI Disclaimer

Open Graph Description: PR5 of the V2 server-side refactor (Transport → Dispatcher → ServerRunner → Server registry). Stacked on #PR4 (maxisbey/v2-server-runner). Status: WIP — chunks A+B landed, chunk C (additive new-pat...

X Description: PR5 of the V2 server-side refactor (Transport → Dispatcher → ServerRunner → Server registry). Stacked on #PR4 (maxisbey/v2-server-runner). Status: WIP — chunks A+B landed, chunk C (additive new-pat...

Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/pull/2562

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