fix: timeout 0 means no timeout in ServerSession.send_request

BaseSession applied the timeout with `request_read_timeout_seconds or
session_read_timeout_seconds`, so 0 fell through to "no timeout" -
ClientSession still reads it that way. The `is not None` check here made
the two session classes interpret 0 oppositely.

Author: maxisbey

src/mcp/server/session.py

@@ -71,7 +71,7 @@ async def send_request(
         """
         data = request.model_dump(by_alias=True, mode="json", exclude_none=True)
         opts: CallOptions = {}
-        if request_read_timeout_seconds is not None:
+        if request_read_timeout_seconds:
             opts["timeout"] = request_read_timeout_seconds
         if progress_callback is not None:
             opts["on_progress"] = progress_callback

tests/server/test_session.py

@@ -99,6 +99,16 @@ async def test_send_request_omits_call_options_when_none_given():
     assert related is None
 
 
+@pytest.mark.anyio
+async def test_send_request_timeout_zero_means_no_timeout():
+    """0 falls through BaseSession's `or`-fallback, so it has always meant
+    "no timeout"; ClientSession still reads it that way."""
+    dispatcher = StubDispatcher(result={})
+    session = _make_session(dispatcher)
+    await session.send_request(types.PingRequest(), types.EmptyResult, request_read_timeout_seconds=0)
+    assert dispatcher.requests[0][2] is None
+
+
 @pytest.mark.anyio
 async def test_send_request_without_back_channel_or_related_id_fails_fast():
     """No standalone channel and no related request to ride on: raise instead