I'd argue that this isn't really a prompt problem, though. For example, when using typical Unix terminals, I refuse to mouse copy/paste when logged in as root

I'd argue that this isn't really a prompt problem, though. For example, when using typical Unix terminals, I refuse to mouse copy/paste when logged in as root (whether or not the prompt is nearby), because it's too easy to make a mistake and the consequences are severe. Similarly, I refuse to rely on any cute shell tricks like "!" to pull history items when logged in as root. Sacrifice convenience to guarantee safety. I also prefer to use my Mac terminal (MacTelnet), which will trap multi-line pastes and offer options to paste as-is, paste as one line, or cancel the operation. This has saved me more than once.