설명해서가 아니라 설계부터 설명 가능하게

EVENT_WEIGHTS = {
    "saved_at":    4.0,   # filing it is the strongest positive act
    "liked_at":    3.0,
    "shared_at":   3.0,
    "read_at":     1.0,   # opening is weak evidence, but it is evidence
    "disliked_at": -4.0,  # an explicit verdict, weighted like a save
}
FRESHNESS_WEIGHT = 1.5
KW_SCALE = 0.5
KW_MATCH_CAP = 6          # surface area must not beat relevance


def features(article: dict) -> dict[str, float]:
    """Namespaced strings. Every score term will be nameable because
    every feature already has a name."""
    feats = {f"outlet:{article['outlet']}": 1.0,
             f"source:{article['source_id']}": 1.0}
    for tok in tokens(article):
        feats[f"kw:{tok}"] = KW_SCALE
    return feats


def score(article: dict, profile: dict[str, float], now) -> tuple[float, list]:
    """Returns (score, why). `why` is not a story ABOUT the score -- it
    is the largest terms IN it, so the two cannot drift apart."""
    total, terms, matches = 0.0, [], 0
    for key, scale in features(article).items():
        weight = profile.get(key)
        if not weight:
            continue
        if key.startswith("kw:"):
            if matches >= KW_MATCH_CAP:
                continue
            matches += 1
        contribution = weight * scale
        total += contribution
        terms.append((key, round(contribution, 2)))

    fresh = FRESHNESS_WEIGHT * decay(article["published_at"], now,
                                    FRESHNESS_HALF_LIFE_DAYS)
    total += fresh
    # NOTE, and this is the shipped behaviour rather than the ideal
    # one: freshness moves the total but is NOT appended to `terms`,
    # so a card ranked partly by recency never says so. Appending it
    # here is the one-line fix; leaving it out is how a "cannot
    # drift" guarantee quietly becomes a convention. The shipped
    # fallback is `why or "fresh"`, which covers the empty case
    # and hides the mixed one -- the harder half.

    terms.sort(key=lambda t: -abs(t[1]))
    return total, terms[:3]        # travels with the row, in the payload