/dev/ptmx at checkPhase

Here’s the line that I would guess is failing.

Is there any way to make available /dev/ptmx at checkPhase?

Would that be an impurity?

I see the sandbox-paths option but that wouldn’t be an ideal solution for a public flake, would it? Or am I missing something?

I had the idea of creating my own /dev/ptmx in the sandbox but I’m not sure whether that’s a good thread to pull on.

Please illumine me.