[WIP] fix(sse): Remove manual cancel_scope.cancel() to prevent task lifecycle violation

src/mcp/client/sse.py

@@ -111,7 +111,11 @@ async def sse_reader(
                             raise sse_exc
                         except Exception as exc:
                             logger.exception("Error in sse_reader")
-                            await read_stream_writer.send(exc)
+                            try:
+                                await read_stream_writer.send(exc)
+                            except anyio.ClosedResourceError:
+                                # Stream already closed during shutdown, which is expected
+                                logger.debug("Stream closed during error handling - ignoring")
                         finally:
                             await read_stream_writer.aclose()
 
@@ -142,7 +146,13 @@ async def post_writer(endpoint_url: str):
                     try:
                         yield read_stream, write_stream
                     finally:
-                        tg.cancel_scope.cancel()
+                        # FIX: Removed manual tg.cancel_scope.cancel() that violated anyio lifecycle
+                        # The original code called tg.cancel_scope.cancel() here, but this caused:
+                        # "RuntimeError: Attempted to exit cancel scope in a different task than it was entered in"
+                        #
+                        # The task group's __aexit__ will properly cancel all child tasks when
+                        # this context manager exits, so no manual cancellation is needed.
+                        pass
         finally:
             await read_stream_writer.aclose()
             await write_stream.aclose()