Consumers That Tolerate Repeats

This is the method the store's points ledger used to credit loyalty points:

static void plainIncrement(Connection db, ConsumerRecord<String, String> r) throws SQLException {
    try (var add = db.prepareStatement("UPDATE accounts_plain SET points = points + ? WHERE customer_id = ?")) {
        add.setInt(1, points(r));
        add.setString(2, r.key());
        add.executeUpdate();
    }
}

It is correct for every event delivered exactly once, and wrong for every event delivered twice

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