Fix ClientSession swallowing exceptions in default message_handler

Author: mayuriphad

src/mcp/client/session.py

@@ -250,6 +250,9 @@ async def __call__(self, message: IncomingMessage) -> None: ...  # pragma: no br
 
 
 async def _default_message_handler(message: IncomingMessage) -> None:
+    if isinstance(message, Exception):
+        logger.error("ClientSession Error: %s", message)
+        raise message
     await anyio.lowlevel.checkpoint()