Pass through the actual session ID

Author: localden

src/mcp/server/experimental/request_context.py

@@ -187,7 +187,7 @@ async def work(task: ServerTaskContext) -> CallToolResult:
         # Access task_group via TaskSupport - raises if not in run() context
         task_group = support.task_group
 
-        session_id = str(id(self._session))
+        session_id = self._session.session_id
         task = await support.store.create_task(self.task_metadata, task_id, session_id=session_id)
 
         task_ctx = ServerTaskContext(

src/mcp/server/lowlevel/experimental.py

@@ -153,7 +153,7 @@ def enable_tasks(
             async def _default_get_task(
                 ctx: ServerRequestContext[LifespanResultT], params: GetTaskRequestParams
             ) -> GetTaskResult:
-                session_id = str(id(ctx.session))
+                session_id = ctx.session.session_id
                 task = await task_support.store.get_task(params.task_id, session_id=session_id)
                 if task is None:
                     raise MCPError(code=INVALID_PARAMS, message=f"Task not found: {params.task_id}")
@@ -175,7 +175,7 @@ async def _default_get_task_result(
                 ctx: ServerRequestContext[LifespanResultT], params: GetTaskPayloadRequestParams
             ) -> GetTaskPayloadResult:
                 assert ctx.request_id is not None
-                session_id = str(id(ctx.session))
+                session_id = ctx.session.session_id
                 req = GetTaskPayloadRequest(params=params)
                 result = await task_support.handler.handle(req, ctx.session, ctx.request_id, session_id=session_id)
                 return result
@@ -188,7 +188,7 @@ async def _default_list_tasks(
                 ctx: ServerRequestContext[LifespanResultT], params: PaginatedRequestParams | None
             ) -> ListTasksResult:
                 cursor = params.cursor if params else None
-                session_id = str(id(ctx.session))
+                session_id = ctx.session.session_id
                 tasks, next_cursor = await task_support.store.list_tasks(cursor, session_id=session_id)
                 return ListTasksResult(tasks=tasks, next_cursor=next_cursor)
 
@@ -199,7 +199,7 @@ async def _default_list_tasks(
             async def _default_cancel_task(
                 ctx: ServerRequestContext[LifespanResultT], params: CancelTaskRequestParams
             ) -> CancelTaskResult:
-                session_id = str(id(ctx.session))
+                session_id = ctx.session.session_id
                 result = await cancel_task(task_support.store, params.task_id, session_id=session_id)
                 return result
 

src/mcp/server/lowlevel/server.py

@@ -374,6 +374,9 @@ async def run(
         # the initialization lifecycle, but can do so with any available node
         # rather than requiring initialization for each connection.
         stateless: bool = False,
+        # Optional session identifier for task isolation. When provided (e.g.,
+        # from the transport's mcp_session_id), tasks are bound to this ID.
+        session_id: str | None = None,
     ):
         async with AsyncExitStack() as stack:
             lifespan_context = await stack.enter_async_context(self.lifespan(self))
@@ -383,6 +386,7 @@ async def run(
                     write_stream,
                     initialization_options,
                     stateless=stateless,
+                    session_id=session_id,
                 )
             )
 

src/mcp/server/session.py

@@ -83,9 +83,11 @@ def __init__(
         write_stream: MemoryObjectSendStream[SessionMessage],
         init_options: InitializationOptions,
         stateless: bool = False,
+        session_id: str | None = None,
     ) -> None:
         super().__init__(read_stream, write_stream)
         self._stateless = stateless
+        self.session_id = session_id
         self._initialization_state = (
             InitializationState.Initialized if stateless else InitializationState.NotInitialized
         )

src/mcp/server/streamable_http_manager.py

@@ -172,6 +172,7 @@ async def run_stateless_server(*, task_status: TaskStatus[None] = anyio.TASK_STA
                         write_stream,
                         self.app.create_initialization_options(),
                         stateless=True,
+                        session_id=http_transport.mcp_session_id,
                     )
                 except Exception:  # pragma: no cover
                     logger.exception("Stateless session crashed")
@@ -240,6 +241,7 @@ async def run_server(*, task_status: TaskStatus[None] = anyio.TASK_STATUS_IGNORE
                                     write_stream,
                                     self.app.create_initialization_options(),
                                     stateless=False,
+                                    session_id=http_transport.mcp_session_id,
                                 )
 
                             if idle_scope.cancelled_caught: