Narrow message_handler's parameter to notifications and exceptions (#3168)

tests/interaction/README.md

@@ -40,7 +40,7 @@ flows — with a single subprocess test for stdio.
 ```text
 tests/interaction/
   _requirements.py      the requirements manifest (see below)
-  _helpers.py           shared type aliases + the wire-recording transport
+  _helpers.py           the wire-recording transport
   _connect.py           the transport-parametrized connection factories
   conftest.py           the connect fixture (the transport matrix)
   test_coverage.py      enforces the manifest ↔ test contract

tests/interaction/_helpers.py

@@ -1,28 +1,16 @@
 """Shared helpers for the interaction suite.
 
-Keep this module small: it exists only for (a) types that every test would otherwise have to
-assemble from the SDK's internals to annotate a client callback, and (b) the recording transport
-used by the wire-level tests. Server fixtures and assertion helpers belong in the test that uses
-them.
+Keep this module small: it exists only for the recording transport used by the wire-level
+tests. Server fixtures and assertion helpers belong in the test that uses them.
 """
 
 from types import TracebackType
 
 import anyio
-from mcp_types import ClientResult, ServerNotification, ServerRequest
 from typing_extensions import Self
 
 from mcp.client._transport import ReadStream, Transport, TransportStreams, WriteStream
 from mcp.shared.message import SessionMessage
-from mcp.shared.session import RequestResponder
-
-# TODO: this union is the parameter type of every client message handler (MessageHandlerFnT),
-# but the SDK does not export a name for it -- writing a correctly-typed handler requires
-# importing RequestResponder from mcp.shared.session and assembling the union by hand. It
-# should be a named, exported alias next to MessageHandlerFnT (like ClientRequestContext is
-# for the request callbacks), at which point this alias can be deleted.
-IncomingMessage = RequestResponder[ServerRequest, ClientResult] | ServerNotification | Exception
-"""Everything a client message handler can receive."""
 
 
 class _RecordingReadStream:

tests/interaction/lowlevel/test_cancellation.py

@@ -29,13 +29,12 @@ from mcp_types import (
 )
 
 from mcp import MCPError
-from mcp.client import ClientRequestContext, ClientSession
+from mcp.client import ClientRequestContext, ClientSession, IncomingMessage
 from mcp.server import Server, ServerRequestContext
 from mcp.shared.memory import MessageStream, create_client_server_memory_streams
 from mcp.shared.message import SessionMessage
 from tests._stamp import Unstamp
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/lowlevel/test_elicitation.py

@@ -28,12 +28,11 @@ from mcp_types import (
 )
 
 from mcp import MCPError, UrlElicitationRequiredError
-from mcp.client import ClientRequestContext, ClientSession
+from mcp.client import ClientRequestContext, ClientSession, IncomingMessage
 from mcp.server import Server, ServerRequestContext
 from mcp.shared.memory import MessageStream, create_client_server_memory_streams
 from mcp.shared.message import SessionMessage
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/lowlevel/test_flows.py

@@ -29,12 +29,11 @@ from mcp_types import (
 )
 
 from mcp import MCPError, UrlElicitationRequiredError
-from mcp.client import ClientRequestContext
+from mcp.client import ClientRequestContext, IncomingMessage
 from mcp.server import Server, ServerRequestContext
 from mcp.server.session import ServerSession
 from tests._stamp import Unstamp
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/lowlevel/test_list_changed.py

@@ -26,9 +26,9 @@ from mcp_types import (
     ToolListChangedNotification,
 )
 
+from mcp.client import IncomingMessage
 from mcp.server import Server, ServerRequestContext
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/lowlevel/test_progress.py

@@ -15,12 +15,12 @@ import pytest
 from inline_snapshot import snapshot
 from mcp_types import CallToolResult, ProgressNotification, ProgressNotificationParams, ProgressToken, TextContent
 
+from mcp.client import IncomingMessage
 from mcp.server import Server, ServerRequestContext
 from mcp.server.session import ServerSession
-from mcp.shared.session import ProgressFnT
+from mcp.shared.dispatcher import ProgressFnT
 from tests._stamp import Unstamp
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/lowlevel/test_resources.py

@@ -26,10 +26,10 @@ from mcp_types import (
 )
 
 from mcp import MCPError
+from mcp.client import IncomingMessage
 from mcp.server import Server, ServerRequestContext
 from tests._stamp import Unstamp
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/mcpserver/test_context.py

@@ -17,12 +17,11 @@ from mcp_types import (
 from pydantic import BaseModel
 
 from mcp import MCPError
-from mcp.client import ClientRequestContext
+from mcp.client import ClientRequestContext, IncomingMessage
 from mcp.server.elicitation import AcceptedElicitation
 from mcp.server.mcpserver import Context, MCPServer
 from tests._stamp import Unstamp
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/mcpserver/test_tools.py

@@ -17,12 +17,12 @@ from mcp_types import (
 from pydantic import BaseModel, Field
 
 from mcp import MCPError
+from mcp.client import IncomingMessage
 from mcp.server.mcpserver import Context, MCPServer
 from mcp.server.mcpserver.exceptions import ToolError
 from mcp.shared.exceptions import UrlElicitationRequiredError
 from tests._stamp import Unstamp
 from tests.interaction._connect import Connect
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio

tests/interaction/transports/test_streamable_http.py

@@ -23,12 +23,11 @@ from mcp_types import (
 )
 from pydantic import BaseModel
 
-from mcp.client import ClientRequestContext
+from mcp.client import ClientRequestContext, IncomingMessage
 from mcp.server.elicitation import AcceptedElicitation
 from mcp.server.mcpserver import Context, MCPServer
 from mcp.shared.exceptions import MCPError
 from tests.interaction._connect import connect_over_streamable_http
-from tests.interaction._helpers import IncomingMessage
 from tests.interaction._requirements import requirement
 
 pytestmark = pytest.mark.anyio