They are intended to be fully sandboxed and not have direct internet access. Things like package managers are run from internal proxies.
The environments are built to be as reproducible as possible.
But yeah, the serious folks have been talking about rogue clusters for a long time, eg see Ajeya Cotra’s pod with Dwarkesh.
Not sure why the reproducibility is a requirement that would contribute to the security. Not that fully sandboxing is harder with reproducibility, but that is a moot point when reproducibility isn’t a requirement.
OP pointed out clusters being hijacked specifically being a bigger concern than rogue clusters, your comment hijacks their comment to talk about “rogue clusters.” Or perhaps this is a promotion for Dwarkesh?