Good stuff to know, was just curious since it can be rather annoying when you work on a doodle only to have the chain for it expire or otherwise, incidentally is the expiration on prompts random or is there a set amount of time before one expires?
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If there are no lines added to the doodle, the chain expires in 5 minutes. If there are lines drawn, I think it's about 48h since the last time that the doodle page was refreshed/opened or a line was added, but I'm not entirely sure. If you add a line to a doodle once every day, it should stay active. But if you forget to do that one day, you might lose it.