A periodic notifier that misses nothing and repeats at most one item

Android only. A periodic worker gets two guarantees from the platform and neither is the one you want: it will run eventually, and it will run again. It may also be killed halfway. So the worker itself can hold no memory of what it has done.

Two independent conditions gate each item, and you need both:

// adapted
val items = parseFeed(fetch(FEED_URL))
val now = System.currentTimeMillis()