fix: address coverage gaps and stale RequestSender docstring

- tests: replace unreachable 'return {}' with 'raise NotImplementedError'
  (already in coverage exclude_also) and collapse send_request+return into
  one statement
- dispatcher: RequestSender docstring no longer claims Dispatcher satisfies it
  (Dispatcher exposes call(), not send_request())

Author: maxisbey

src/mcp/shared/dispatcher.py

@@ -66,8 +66,8 @@ class CallOptions(TypedDict, total=False):
 class RequestSender(Protocol):
     """Anything that can send a request and await its result.
 
-    Both `Dispatcher` (for top-level outbound calls) and `DispatchContext`
-    (for server-to-client calls made *during* an inbound request) satisfy this.
+    `DispatchContext` satisfies this; `PeerMixin` (and `Connection`/`Peer`) wrap
+    a `RequestSender` to provide typed request methods.
     """
 
     async def send_request(

tests/shared/test_dispatcher.py

@@ -109,7 +109,7 @@ async def on_call(
         ctx: DispatchContext[TransportContext], method: str, params: Mapping[str, Any] | None
     ) -> dict[str, Any]:
         await anyio.sleep_forever()
-        return {}
+        raise NotImplementedError
 
     async with running_pair(server_on_call=on_call) as (client, *_):
         with anyio.fail_after(5), pytest.raises(MCPError) as exc:
@@ -148,8 +148,7 @@ async def test_ctx_send_request_raises_nobackchannelerror_when_transport_disallo
     async def server_on_call(
         ctx: DispatchContext[TransportContext], method: str, params: Mapping[str, Any] | None
     ) -> dict[str, Any]:
-        await ctx.send_request("sampling/createMessage", None)
-        return {}
+        return await ctx.send_request("sampling/createMessage", None)
 
     async with running_pair(server_on_call=server_on_call, can_send_request=False) as (client, *_):
         with anyio.fail_after(5), pytest.raises(NoBackChannelError) as exc: