Recently, Claude gives you these options when asking you to accept a plan:

  Would you like to proceed?

  > 1. Yes, clear context and auto-accept edits (shift+tab)
    2. Yes, auto-accept edits
    3. Yes, manually approve edits
    4. Type here to tell Claude what to change

So the default is to do it in a new context.

If you examine what this actually does, it clears the context, and then says "here's the plan", points to the plan file, and also points to the logs of the previous discussion so that if it determines it should go back and look at them, it can.