How to use a second keyboard as a separate game controller for SuperTux Kart?

I have a GNU/Linux Debian 12 laptop on which I installed SuperTux Kart using APT. I want two people to be able to play SuperTux Kart on the same computer using two separate keyboards, **with the same keybindings for action/motion keys**. (One keyboard is built into the laptop and the other is plugged in via USB.) This is a challenge because even though I make the two keyboards into separate controllers within SuperTux Kart, the controls still interfere. In other words, both keyboards are treated as a single one, even though they are listed as separate controllers in SuperTux Kart. How do I treat the second keyboard like a separate controller? I don't mind building stuff from source or installing APT packages, but I don't want to install pre-compiled binaries from anywhere else. - **OS:** Debian GNU/Linux 12 (bookworm) x86_64 - **Kernel:** 6.1.0-28-amd64 - **SuperTux Kart version:** 1.4 - **Compositor:** Wayland (X11-dependant solutions won't work)