저장한 건 영원하고, 저장 안 한 건 퇴비야

def prune(con) -> int:
    """The ONLY thing in this system that deletes an article.

    Everything else that wants an article gone must go through here.
    No cascade reaches this table (see the next lesson for why that
    sentence had to be earned), and events survive in the JSONL log
    regardless of what happens to the row they point at.
    """
    cutoff = (datetime.now(timezone.utc)
              - timedelta(days=RETENTION_DAYS)).isoformat(timespec="seconds")
    cur = con.execute(
        """DELETE FROM articles WHERE fetched_at < ?
           AND id NOT IN (
               SELECT article_id FROM article_state
               WHERE saved_at IS NOT NULL OR shared_at IS NOT NULL
           )""",
        (cutoff,),
    )
    con.commit()
    return cur.rowcount


def compost(con) -> dict:
    """Retention covers everything DERIVED, not only articles. Each
    derived artifact ages out against the lifetime of what it explains."""
    return {
        "articles":      prune(con),
        "fetch_log":     prune_fetch_log(con),      # diagnostic, not truth
        "trend_samples": prune_trend_samples(con),  # per-topic depth
        "tts_cache":     prune_tts_cache(con),      # keyed to live articles
    }