Do I try and port #picom to #buildroot so there's a compositor available for me, or do I rewrite the #WebkitGTK browser to use #WPEWebKit instead?

Everything will be running on modern x86_64 hardware, with integrated intel graphics, so I'm leaning towards picom.

#picom successfully given the #buildroot makeover.

Buildroot kiosk successfully booting to the WebGL page on real hardware, next to try it on the target hardware.

I'm still not sure if #picom was the solution, given that it still fails in #qemu, but that's probably the GL pass-through/emulation being sketch.

Still, for this endeavour, qemu has been invaluable.