fix: stop infinite GET stream reconnection on repeated empty connections

Only reset the attempt counter when events were actually received
during the connection. Connections that close immediately without
delivering events now count toward MAX_RECONNECTION_ATTEMPTS.

Github-Issue:#1401

Author: heyhayes

src/mcp/client/streamable_http.py

@@ -197,7 +197,9 @@ async def handle_get_stream(self, client: httpx.AsyncClient, read_stream_writer:
                     event_source.response.raise_for_status()
                     logger.debug("GET SSE connection established")
 
+                    received_events = False
                     async for sse in event_source.aiter_sse():
+                        received_events = True
                         # Track last event ID for reconnection
                         if sse.id:
                             last_event_id = sse.id
@@ -207,8 +209,12 @@ async def handle_get_stream(self, client: httpx.AsyncClient, read_stream_writer:
 
                         await self._handle_sse_event(sse, read_stream_writer)
 
-                    # Stream ended normally (server closed) - reset attempt counter
-                    attempt = 0
+                    # Only reset attempts if we actually received events;
+                    # empty connections count toward MAX_RECONNECTION_ATTEMPTS
+                    if received_events:
+                        attempt = 0
+                    else:
+                        attempt += 1
 
             except Exception:  # pragma: lax no cover
                 logger.debug("GET stream error", exc_info=True)