The game "openAstroMenace", for some reason defaults to using VBO Core in the absence of VAO core, which predictably causes the game to crash on a modern OpenGL implementation. The game itself crashing is not a problem; it's the PSU switching off that's very concerning.

I'm running an ASRock E3V5 WS motherboard with a 4 GB Sapphire R9 Fury X, and an E3-1235L CPU.

I'm early on in diagnosing it so I don't have a stack trace, but I think I've ruled out hardware problems, as this system doesn't break a sweat maxing out the Heaven benchmark or the Phoronix JuliaGPU (via ROCm) benchmark, and plays every other game flawlessly. It can run with all CPU cores at 100% for hours on end. openAstroMenace runs flawlessly with max settings when VAO Core is enabled.

Mesa may be malfunctioning here, but a userspace library wouldn't affect PSU behavior. This is pointing me in the direction of suspecting AMDGPU to be the culprit. It exhibits this behavior on both my Ubuntu and Gentoo installations, and on 4.15 and 4.18 series kernels. The system poweroff is predictable down to less than half a second, and is triggered exactly the same way at exactly the same time in every instance. It occurs around 3/4 of a second after the game's menu appears.