fix: Handle mixed tool and non-tool parts in LiteLLM content conversion

When converting a `types.Content` to LiteLLM messages, if the content contains both `function_response` parts and other types of parts (e.g., text, image), the function now generates a list of LiteLLM messages

Close #4091

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 854240746

src/google/adk/models/lite_llm.py

@@ -461,7 +461,8 @@ async def _content_to_message_param(
     A litellm Message, a list of litellm Messages.
   """
 
-  tool_messages = []
+  tool_messages: list[Message] = []
+  non_tool_parts: list[types.Part] = []
   for part in content.parts:
     if part.function_response:
       response = part.function_response.response
@@ -477,9 +478,22 @@ async def _content_to_message_param(
               content=response_content,
           )
       )
-  if tool_messages:
+    else:
+      non_tool_parts.append(part)
+
+  if tool_messages and not non_tool_parts:
     return tool_messages if len(tool_messages) > 1 else tool_messages[0]
 
+  if tool_messages and non_tool_parts:
+    follow_up = await _content_to_message_param(
+        types.Content(role=content.role, parts=non_tool_parts),
+        provider=provider,
+    )
+    follow_up_messages = (
+        follow_up if isinstance(follow_up, list) else [follow_up]
+    )
+    return tool_messages + follow_up_messages
+
   # Handle user or assistant messages
   role = _to_litellm_role(content.role)
 

tests/unittests/models/test_litellm.py

@@ -1813,6 +1813,46 @@ async def test_content_to_message_param_multi_part_function_response():
   assert messages[1]["content"] == '{"value": 123}'
 
 
+@pytest.mark.asyncio
+async def test_content_to_message_param_function_response_with_extra_parts():
+  tool_part = types.Part.from_function_response(
+      name="load_image",
+      response={"status": "success"},
+  )
+  tool_part.function_response.id = "tool_call_1"
+
+  text_part = types.Part.from_text(text="[Image: img_123.png]")
+  image_bytes = b"test_image_data"
+  image_part = types.Part.from_bytes(data=image_bytes, mime_type="image/png")
+
+  content = types.Content(
+      role="user",
+      parts=[tool_part, text_part, image_part],
+  )
+
+  messages = await _content_to_message_param(content)
+  assert isinstance(messages, list)
+  assert messages == [
+      {
+          "role": "tool",
+          "tool_call_id": "tool_call_1",
+          "content": '{"status": "success"}',
+      },
+      {
+          "role": "user",
+          "content": [
+              {"type": "text", "text": "[Image: img_123.png]"},
+              {
+                  "type": "image_url",
+                  "image_url": {
+                      "url": "data:image/png;base64,dGVzdF9pbWFnZV9kYXRh"
+                  },
+              },
+          ],
+      },
+  ]
+
+
 @pytest.mark.asyncio
 async def test_content_to_message_param_function_response_preserves_string():
   """Tests that string responses are used directly without double-serialization.