Maybe not for very broad definitions of OS state, but for specific files/folders/filesystems, this is trivial with FS-level snapshots and copy-on-write.

Let's assume that you can. For disaster recovery, this is probably acceptable, but it's unacceptable for basically any other purpose. Reverting the whole state of the machine because the AI agent (a single tenant in what is effectively a multi-tenant system) did something thing incorrect is unacceptable. Managing undo/redo in a multiplayer environment is horrific.

I wonder if in the long run this will lead to the ascent of NixOS. They seem perfect for each other: if you have git and/or a snapshotting filesystem, together with the entire system state being downstram of your .nix file, then go ahead and let the LLM make changes willy-nilly, you can always roll back to a known good version.

NixOS still isn't ready for this world, but if it becomes the natural counterpart to LLM OS tooling, maybe that will speed up development.

Well there is cri-u for what its worth on linux which can atleast snapshot the state of an application and I suppose something must be similar available for filesystems as well

Also one can simply run a virtual machine which can do that but then the issue becomes in how apps from outside connect to vm inside

At least on macOS, an OS snapshot is a thing [1]; I suspect Cowork will mostly run in a sandbox, which Claude Code does now.

[1]: https://www.cleverfiles.com/help/apfs-snapshots.html

Sure you can. Filesystem snapshotting is available on all OSes now.