This is a weak deduper to make things like bulk email run safer. It is not a lock safe for financial/security needs because it uses a weak redis locking pattern that can have race conditions. However, imagine a bulk email job that loops over 100 users, and enqueues a background email for each user. If the job fails at iteration 50, a retry would enqueue all the users again and many will receive dupes. This would continue multiple times as the parent job continued to rerun. By marking that a subjob has been enqueued, we can let that isolated job handle its own failures, and the batch enqueue job can run multiple times without re-enqueueing the same subjobs.