fix(sambanova): emit empty delta on usage-only final stream chunk

SambaNovaCloud enables stream_options={'include_usage': True} by default,
so the stream ends with a usage-only chunk where choices == []. That chunk
takes the else branch, which never reassigns content_delta, so the final
yield re-emits the previous chunk's token as its delta. This breaks the
streaming invariant that ''.join(deltas) equals the final message.content.

Set content_delta to '' on the usage-only chunk. Adds a regression test
that stubs the streaming request and asserts the concatenated deltas equal
the final content.

Author: ebarkhordar

llama-index-integrations/llms/llama-index-llms-sambanovasystems/llama_index/llms/sambanovasystems/base.py

@@ -551,6 +551,10 @@ def stream_chat(
                     ),
                 }
             else:
+                # A usage-only / final chunk has choices == [] and carries no new
+                # text, so its delta must be empty; otherwise the previous chunk's
+                # content_delta is re-emitted and "".join(deltas) != message.content.
+                content_delta = ""
                 additional_kwargs = {
                     "id": partial_response["id"],
                     "finish_reason": finish_reason,

llama-index-integrations/llms/llama-index-llms-sambanovasystems/pyproject.toml

@@ -26,7 +26,7 @@ dev = [
 
 [project]
 name = "llama-index-llms-sambanovasystems"
-version = "0.6.0"
+version = "0.6.1"
 description = "llama-index llms sambanova cloud and sambastudio integration"
 authors = [{name = "Rodrigo Maldonado", email = "rodrigo.maldonado@pucp.edu.pe"}]
 requires-python = ">=3.10,<4.0"

llama-index-integrations/llms/llama-index-llms-sambanovasystems/tests/test_llms_sambanovasystems.py

@@ -214,6 +214,35 @@ def test_init():
     _ = SambaStudio(sambastudio_url="fake/stream/url", sambastudio_api_key="fake")
 
 
+def test_stream_chat_usage_chunk_emits_empty_delta():
+    """Usage-only final chunk (choices == []) must yield an empty delta so concatenated deltas equal the final content."""
+    client = SambaNovaCloud(sambanova_api_key="fake")
+
+    def fake_streaming_request(messages_dicts, stop=None):
+        yield {
+            "id": "id-0",
+            "choices": [{"delta": {"content": "Hello"}, "finish_reason": None}],
+        }
+        # include_usage=True (the default) appends a trailing usage-only chunk
+        yield {
+            "id": "id-0",
+            "choices": [],
+            "usage": {"total_tokens": 5},
+            "model": "Meta-Llama-3.1-8B-Instruct",
+            "system_fingerprint": "fp",
+            "created": 1,
+        }
+
+    client._handle_streaming_request = fake_streaming_request
+
+    messages = [ChatMessage(role=MessageRole.USER, content="hi")]
+    responses = list(client.stream_chat(messages))
+
+    joined_deltas = "".join(r.delta for r in responses)
+    assert joined_deltas == responses[-1].message.content == "Hello"
+    assert responses[-1].delta == ""
+
+
 if __name__ == "__main__":
     test_sambanovacloud()
     test_sambastudio()