Python: Preserve metadata when merging streaming text content

python/semantic_kernel/contents/streaming_text_content.py

@@ -49,7 +49,7 @@ def __add__(self, other: TextContent) -> "StreamingTextContent":
             choice_index=self.choice_index,
             inner_content=self._merge_inner_contents(other.inner_content),
             ai_model_id=self.ai_model_id,
-            metadata=self.metadata,
+            metadata=self.metadata | other.metadata,
             text=(self.text or "") + (other.text or ""),
             encoding=self.encoding,
         )

python/tests/unit/contents/test_streaming_text_content.py

@@ -0,0 +1,26 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+from semantic_kernel.contents.streaming_text_content import StreamingTextContent
+
+
+def test_stc_add_combines_metadata():
+    chunk1 = StreamingTextContent(choice_index=0, text="Hello, ", metadata={"id": "cmpl-1"})
+    chunk2 = StreamingTextContent(choice_index=0, text="world!", metadata={"usage": {"prompt_tokens": 5}})
+
+    combined = chunk1 + chunk2
+
+    assert combined.text == "Hello, world!"
+    assert combined.metadata == {"id": "cmpl-1", "usage": {"prompt_tokens": 5}}
+
+    # Make sure the original metadata is preserved
+    assert chunk1.metadata == {"id": "cmpl-1"}
+    assert chunk2.metadata == {"usage": {"prompt_tokens": 5}}
+
+
+def test_stc_add_metadata_conflicting_keys_other_wins():
+    chunk1 = StreamingTextContent(choice_index=0, text="Hello, ", metadata={"id": "cmpl-1", "logprobs": None})
+    chunk2 = StreamingTextContent(choice_index=0, text="world!", metadata={"logprobs": {"tokens": ["world!"]}})
+
+    combined = chunk1 + chunk2
+
+    assert combined.metadata == {"id": "cmpl-1", "logprobs": {"tokens": ["world!"]}}