Reading scores without being misled

def _lightweight_scores(question, answer, contexts, ground_truth):
    """Heuristic fallback when RAGAS isn't available."""
    if not answer or not contexts:
        return EvalScore(faithfulness=0.0, answer_relevance=0.0, context_precision=0.0, context_recall=0.0)

    joined_ctx = " ".join(contexts).lower()
    answer_words = {w for w in answer.lower().split() if len(w) > 3}
    ctx_words = {w for w in joined_ctx.split() if len(w) > 3}
    q_words = {w for w in question.lower().split() if len(w) > 3}

    faithfulness = len(answer_words & ctx_words) / max(len(answer_words), 1)
    answer_relevance = len(answer_words & q_words) / max(len(q_words), 1)
    context_precision = len(ctx_words & q_words) / max(len(ctx_words), 1)
    return EvalScore(
        faithfulness=round(min(faithfulness, 1.0), 3),
        answer_relevance=round(min(answer_relevance, 1.0), 3),
        context_precision=round(min(context_precision, 1.0), 3),
    )