Fix Mutable Default

The model receives the prompt (and optional system message). The run uses scorer contains_all with the JSON configuration below. Pass/fail and partial credit are determined entirely by that scorer against the model output; no human grading.

Fix the bug and return corrected Python code only.

def add_tag(tag, tags=[]):
    tags.append(tag)
    return tags

{
  "expected_contains": [
    "tags=None",
    "if tags is None",
    "tags.append(tag)"
  ]
}