QEMU virtual machines. Sandboxes like firejail and bubblewrap share a kernel: attacker is one exploit away from root. Hypervisors present an infinitely smaller attack surface, and if they're ever defeated the entire industry is done, not just me.

I have a base system image that gets forked off into delta qcow2 images for every project I'm working on or whatever ephemeral execution context I need.

I started a side project to build software just to manage those VMs. I'm daily driving this thing even though it's my first "vibecoded" project, it's just way too useful and has saved me quite a few times from accidents.

https://github.com/matheusmoreira/virtdev

The firewall works but it's pretty clunky. I'm working on a custom Rust network stack to replace it.

You'd probably prefer something that isn't literally made by one guy and his AIs though. Docker sandboxes seem to be a good solution that also employs virtualization.

https://news.ycombinator.com/item?id=49239751

Before I made all this, I used to use firejail.