Even if they don't know the tools or languages, which in our case they're almost certainly not going to (Rust, Agda, TLA+, etc.), you get to see how they intera

Even if they don't know the tools or languages, which in our case they're almost certainly not going to (Rust, Agda, TLA+, etc.), you get to see how they interact with a situation where they need to be able to direct some of their own learning by seeing if they ask questions, if they can synthesize insights despite lack of deep familiarity, how they react to having naivety exposed, etc. Most of the challenging work is collaborative problem solving, not exam proctoring, and it's important to see how a person interacts with that. You'll see how much direction they're likely to need, if they can navigate and contribute positively to team dynamics, and so on.