class Message:
    def __init__(self, content: str | None = None) -> None:
        self.content = content

def has_error_marker(messages: list[Message]) -> bool:
    if (
        len(messages) > 0
        and messages[-1].content  # narrows str | None -> str
        and "[ERROR]" in messages[-1].content  # pyrefly: `in` ... and `None`
    ):
        return True
    return False