Revert "refactor: reorganize message handling for better type safety and clar…" (#282)

This reverts commit 9d0f2daddb.

src/mcp/shared/memory.py

@@ -11,11 +11,11 @@ from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStre
 
 from mcp.client.session import ClientSession, ListRootsFnT, SamplingFnT
 from mcp.server import Server
-from mcp.types import MessageFrame
+from mcp.types import JSONRPCMessage
 
 MessageStream = tuple[
-    MemoryObjectReceiveStream[MessageFrame | Exception],
-    MemoryObjectSendStream[MessageFrame],
+    MemoryObjectReceiveStream[JSONRPCMessage | Exception],
+    MemoryObjectSendStream[JSONRPCMessage],
 ]
 
 
@@ -32,10 +32,10 @@ async def create_client_server_memory_streams() -> (
     """
     # Create streams for both directions
     server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
-        MessageFrame | Exception
+        JSONRPCMessage | Exception
     ](1)
     client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
-        MessageFrame | Exception
+        JSONRPCMessage | Exception
     ](1)
 
     client_streams = (server_to_client_receive, client_to_server_send)
@@ -60,9 +60,12 @@ async def create_connected_server_and_client_session(
 ) -> AsyncGenerator[ClientSession, None]:
     """Creates a ClientSession that is connected to a running MCP server."""
     async with create_client_server_memory_streams() as (
-        (client_read, client_write),
-        (server_read, server_write),
+        client_streams,
+        server_streams,
     ):
+        client_read, client_write = client_streams
+        server_read, server_write = server_streams
+
         # Create a cancel scope for the server task
         async with anyio.create_task_group() as tg:
             tg.start_soon(