chore: import upstream snapshot with attribution

python/assistant-stream/tests/test_data_stream.py

@@ -0,0 +1,17 @@
+import json
+
+from assistant_stream.assistant_stream_chunk import UpdateStateChunk
+from assistant_stream.serialization.data_stream import DataStreamEncoder
+
+
+def test_data_stream_encoder_update_state_shape() -> None:
+    encoder = DataStreamEncoder()
+    operations = [
+        {"type": "append-text", "path": ["messages", "0", "text"], "value": "hi"}
+    ]
+
+    encoded = encoder.encode_chunk(UpdateStateChunk(operations=operations))
+
+    assert encoded.startswith("aui-state:")
+    assert encoded.endswith("\n")
+    assert json.loads(encoded[len("aui-state:") :].strip()) == operations