fix(models): preserve LiteLLM reasoning fragments

Author: he-yufeng

src/google/adk/models/lite_llm.py

@@ -925,7 +925,7 @@ async def _content_to_message_param(
       ):
         reasoning_texts.append(_decode_inline_text_data(part.inline_data.data))
 
-    reasoning_content = _NEW_LINE.join(text for text in reasoning_texts if text)
+    reasoning_content = "".join(text for text in reasoning_texts if text)
     return ChatCompletionAssistantMessage(
         role=role,
         content=final_content,

tests/unittests/models/test_litellm.py

@@ -4898,6 +4898,23 @@ async def test_content_to_message_param_non_anthropic_uses_reasoning_content():
   assert "thinking_blocks" not in result
 
 
+@pytest.mark.asyncio
+async def test_content_to_message_param_preserves_reasoning_fragments():
+  content = types.Content(
+      role="model",
+      parts=[
+          types.Part(text="Step 1: ", thought=True),
+          types.Part(text="inspect", thought=True),
+          types.Part(text=".", thought=True),
+          types.Part(text="Done"),
+      ],
+  )
+
+  result = await _content_to_message_param(content, model="openai/gpt-4o")
+
+  assert result.get("reasoning_content") == "Step 1: inspect."
+
+
 @pytest.mark.asyncio
 async def test_anthropic_thinking_blocks_round_trip():
   """End-to-end: thinking_blocks in response → Part → thinking_blocks out."""