fix(litellm): survive malformed JSON in tool call arguments

src/google/adk/models/lite_llm.py

@@ -2455,9 +2455,24 @@ 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 = _parse_tool_call_arguments(tool_call.function.arguments)
+        except json.JSONDecodeError as exc:
+          # Malformed tool-call arguments are treated as a recoverable model
+          # error rather than a crash: surface empty args so downstream tool
+          # dispatch reports the mismatch back to the model for a retry.
+          logger.warning(
+              "Failed to parse arguments of tool call %r for function %r as"
+              " JSON (%s). Falling back to empty args so the model can"
+              " retry.",
+              tool_call.id,
+              tool_call.function.name,
+              exc,
+          )
+          args = {}
         part = types.Part.from_function_call(
             name=tool_call.function.name,
-            args=_parse_tool_call_arguments(tool_call.function.arguments),
+            args=args,
         )
         function_call = part.function_call
         if function_call is None:

tests/unittests/models/test_litellm.py

@@ -2664,6 +2664,59 @@ def test_message_to_generate_content_response_tool_call_accepts_unquoted_json_ke
   }
 
 
+def test_message_to_generate_content_response_tool_call_with_malformed_json_arguments():
+  message = ChatCompletionAssistantMessage(
+      role="assistant",
+      content=None,
+      tool_calls=[
+          ChatCompletionMessageToolCall(
+              type="function",
+              id="test_tool_call_id",
+              function=Function(
+                  name="test_function",
+                  arguments='{"city": "unterminated',
+              ),
+          )
+      ],
+  )
+
+  response = _message_to_generate_content_response(message)
+
+  assert response.content.role == "model"
+  assert response.content.parts[0].function_call.name == "test_function"
+  assert response.content.parts[0].function_call.id == "test_tool_call_id"
+  assert response.content.parts[0].function_call.args == {}
+
+
+def test_message_to_generate_content_response_tool_call_malformed_json_warns(
+    caplog,
+):
+  message = ChatCompletionAssistantMessage(
+      role="assistant",
+      content=None,
+      tool_calls=[
+          ChatCompletionMessageToolCall(
+              type="function",
+              id="test_tool_call_id",
+              function=Function(
+                  name="test_function",
+                  arguments='{"city": "unterminated',
+              ),
+          )
+      ],
+  )
+
+  with caplog.at_level(logging.WARNING, logger="google_adk"):
+    response = _message_to_generate_content_response(message)
+
+  assert response.content.parts[0].function_call.args == {}
+  assert any(
+      record.levelno >= logging.WARNING
+      for record in caplog.records
+      if "Failed to parse arguments" in record.getMessage()
+  )
+
+
 def test_message_to_generate_content_response_inline_tool_call_text():
   message = ChatCompletionAssistantMessage(
       role="assistant",