They do start "drifting" after a while, at which point I export the chat (using Cursor), then start a new chat and add the exported file and say "here's the previous conversation, let's continue where we left off". I find that it deals with the transition pretty well.

It's not often that I have to do this. As I mentioned in my post above, if I start the interaction with thorough instructions/specs, then the conversation concludes before the drift starts to happen.