Fix hanging on streams when stdio_client exiting

src/mcp/client/stdio/__init__.py

@@ -177,6 +177,8 @@ async def stdin_writer():
                 await terminate_windows_process(process)
             else:
                 process.terminate()
+            read_stream.close()
+            write_stream.close()
 
 
 def _get_executable_command(command: str) -> str:

tests/client/test_stdio_cm.py

@@ -0,0 +1,13 @@
+import pytest
+
+from mcp import StdioServerParameters
+from mcp.client.stdio import stdio_client
+
+
+@pytest.mark.anyio
+async def test_context_manager_exiting():
+    async with stdio_client(StdioServerParameters(command="tee")) as (
+        read_stream,
+        write_stream,
+    ):
+        pass