Fix handle sse disconnect

Author: Hoa Lam

src/mcp/server/sse.py

@@ -43,7 +43,7 @@ async def handle_sse(request):
 from sse_starlette import EventSourceResponse
 from starlette.requests import Request
 from starlette.responses import Response
-from starlette.types import Receive, Scope, Send
+from starlette.types import Message, Receive, Scope, Send
 
 import mcp.types as types
 
@@ -120,9 +120,15 @@ async def sse_writer():
                         }
                     )
 
+        async def handle_see_disconnect(message: Message) -> None:
+            logger.debug(f"Disconnect sse {session_id}")
+            del self._read_stream_writers[session_id]
+
         async with anyio.create_task_group() as tg:
             response = EventSourceResponse(
-                content=sse_stream_reader, data_sender_callable=sse_writer
+                content=sse_stream_reader,
+                data_sender_callable=sse_writer,
+                client_close_handler_callable=handle_see_disconnect,  # type: ignore
             )
             logger.debug("Starting SSE response task")
             tg.start_soon(response, scope, receive, send)