I'd be interested in seeing if I'm in the minority but there's no world where I'm agreeing to download bespoke software in order to participate in an interview.

>I kept seeing candidates produce near-perfect solutions while struggling to explain even basic trade-offs. Some would go quiet for long stretches, then suddenly type out optimal code extremely quickly. When I probed deeper, it became obvious that what they were writing didn’t match their level of understanding.

Why do you need a tool to detect cheating? Your 'analogue' approach here is the correct one.