Right now, as soon as you have met the criteria for a challenge, your solution automatically submits itself and your points are awarded. It would be nice if you had a way to delay submission of the challenge until you choose–especially for the puzzles where you are trying to include as many g-u pairs as you can. I have had one of those puzzles end prematurely because I met the criteria by accident. Also, sometimes I am exploring strategy ideas on a puzzle and it is jarring to have the puzzle end unexpectedly because something I just tried worked too well.
There is always the “stay” button at the end of the level.
I did go back and see that you could make changes to improve your rank on the challenges. The interruption is still very jarring, and I’m working around it by not solving the lower level puzzles.
Because of the extra restrictions in place for the hither level puzzles, I am generally not unpleasantly surprised by an interruption on those when I get interested enough to explore an idea.