Every time I add or complete a task, ChatGPT outputs the latest complete copy of my task list (I only had to ask it to do this the first time, then it just did that automatically). So, in other words, it always updates the latest "live state" in its most recent message. If I hit the limit on context window it would just take me ~30 seconds to open up a new window with my original prompt and the latest iteration of my task list if I so desired.

Here's where I posted a snippet of this convo a couple weeks ago: https://news.ycombinator.com/item?id=35390644