약속을 깨뜨린 외래 키

def _detach_articles_from_source_cascade(con) -> None:
    """Rebuild `articles` so deleting a source can never delete one.

    The original FK was ON DELETE CASCADE, which quietly made the
    permanence invariant a lie: deleting a shelf deletes the sources no
    other shelf holds, and the cascade took the saved articles with them
    -- the one thing the product promises never to lose.
    """
    # Detect from the LIVE definition, not from a version flag: the
    # database is asked what is true rather than told what should be.
    fks = con.execute("PRAGMA foreign_key_list(articles)").fetchall()
    if not any(r["from"] == "source_id"
               and str(r["on_delete"]).upper() == "CASCADE"
               for r in fks):
        return                      # already correct; idempotent

    con.commit()                    # PRAGMA is a no-op inside a txn
    con.execute("PRAGMA foreign_keys=OFF")
    try:
        con.execute("BEGIN")
        con.execute("""CREATE TABLE articles_rebuild (
            id        INTEGER PRIMARY KEY,
            -- SET NULL, never CASCADE: an article's permanence must not
            -- depend on the plumbing that delivered it.
            source_id INTEGER REFERENCES sources(id) ON DELETE SET NULL,
            ...
        )""")
        con.execute("INSERT INTO articles_rebuild SELECT * FROM articles")
        con.execute("DROP TABLE articles")
        con.execute("ALTER TABLE articles_rebuild RENAME TO articles")
        con.commit()
    finally:
        con.execute("PRAGMA foreign_keys=ON")


# The other half of the same fix. An INNER join here would drop exactly
# the orphans the rebuild just rescued -- the same disappearance, one
# layer up, and far harder to see.
_ARTICLE_SELECT = """
    SELECT a.*, COALESCE(s.name, '(source removed)') AS source_name
      FROM articles a
      LEFT JOIN sources s ON s.id = a.source_id
"""