What about wands of far slaying? If I put a massive charge in it, I can easily get a range of a couple hundred squares on it. Should I be able to use this prompt to be able to figure out the correct direction to zap the wand so I won't fry myself? Or is there an inherent danger to using a long range weapon where it is difficult to predict the outcome? What if I have a bolt spell with spellpower 200 or so where my bolts can have comparable range? What if my character has poor perception but normal bolt ranges, and there's a wall somewhere I can't see that will reflect the spell back at me when I attack a monster with it? Should I be able to use the prompt to protect my character against threats that they can't even see? What if I'm in darkness, blind, confused, etc.? What if I'm in the room where the directions are reversed?
In the particular case of bouncing bolts, if there must be a prompt, my inclination would be to only have a prompt if the PC targets the bolt directly into an adjacent wall. There seem to be few enough circumstances where doing such a thing would ever be intentional, and minimal ways that it could ever be exploited that having a safety catch for that particular case is probably fine. If you're shooting into an empty square and the bolt reflects at some later point and hits you, well, tough. And it should be turned off in the room where the directions are reversed, because the whole point in those areas is that the UI is supposed to be screwing with you.