Handle BrokenResourceError in stdio client shutdown path

src/mcp/client/stdio.py

@@ -158,7 +158,7 @@ async def stdout_reader():
 
                         session_message = SessionMessage(message)
                         await read_stream_writer.send(session_message)
-        except anyio.ClosedResourceError:  # pragma: lax no cover
+        except (anyio.ClosedResourceError, anyio.BrokenResourceError):  # pragma: lax no cover
             await anyio.lowlevel.checkpoint()
 
     async def stdin_writer():
@@ -174,7 +174,7 @@ async def stdin_writer():
                             errors=server.encoding_error_handler,
                         )
                     )
-        except anyio.ClosedResourceError:  # pragma: no cover
+        except (anyio.ClosedResourceError, anyio.BrokenResourceError):  # pragma: no cover
             await anyio.lowlevel.checkpoint()
 
     async with anyio.create_task_group() as tg, process:

tests/client/test_stdio.py

@@ -86,6 +86,20 @@ async def test_stdio_client_bad_path():
             assert "Connection closed" in exc_info.value.error.message
 
 
+@pytest.mark.anyio
+async def test_stdio_client_exits_immediately_surfaces_connection_closed():
+    """Regression test for #1564: process exit should not bubble BrokenResourceError."""
+    server_params = StdioServerParameters(command=sys.executable, args=["-c", "import sys; sys.exit(0)"])
+
+    async with stdio_client(server_params) as (read_stream, write_stream):
+        async with ClientSession(read_stream, write_stream) as session:
+            with pytest.raises(MCPError) as exc_info:
+                await session.initialize()
+
+            assert exc_info.value.error.code == CONNECTION_CLOSED
+            assert "Connection closed" in exc_info.value.error.message
+
+
 @pytest.mark.anyio
 async def test_stdio_client_nonexistent_command():
     """Test that stdio_client raises an error for non-existent commands."""