fix: handle malformed JSON in tool_call.function.arguments gracefully

src/google/adk/models/lite_llm.py

@@ -1725,9 +1725,20 @@ def _message_to_generate_content_response(
     for tool_call in tool_calls:
       if tool_call.type == "function":
         thought_signature = _extract_thought_signature_from_tool_call(tool_call)
+        try:
+          args = json.loads(tool_call.function.arguments or "{}")
+        except json.JSONDecodeError:
+          logger.warning(
+              "Failed to parse tool_call.function.arguments as JSON for"
+              " tool_call.id=%s, tool_call.function.name=%s: %s",
+              tool_call.id,
+              tool_call.function.name,
+              tool_call.function.arguments,
+          )
+          args = {}
         part = types.Part.from_function_call(
             name=tool_call.function.name,
-            args=json.loads(tool_call.function.arguments or "{}"),
+            args=args,
         )
         part.function_call.id = tool_call.id
         if thought_signature:

tests/unittests/models/test_litellm.py

@@ -2253,6 +2253,30 @@ def test_message_to_generate_content_response_tool_call():
   assert response.content.parts[0].function_call.id == "test_tool_call_id"
 
 
+def test_message_to_generate_content_response_malformed_tool_args_json():
+  """Malformed JSON in tool_call.function.arguments should not crash."""
+  message = ChatCompletionAssistantMessage(
+      role="assistant",
+      content=None,
+      tool_calls=[
+          ChatCompletionMessageToolCall(
+              type="function",
+              id="malformed_call_id",
+              function=Function(
+                  name="demo_tool",
+                  arguments='{"city":"unterminated',
+              ),
+          )
+      ],
+  )
+
+  response = _message_to_generate_content_response(message)
+  assert response.content.role == "model"
+  assert response.content.parts[0].function_call.name == "demo_tool"
+  assert response.content.parts[0].function_call.args == {}
+  assert response.content.parts[0].function_call.id == "malformed_call_id"
+
+
 def test_message_to_generate_content_response_inline_tool_call_text():
   message = ChatCompletionAssistantMessage(
       role="assistant",