> Free idea: I would like to be able to "jail" an agent inside a VM and send instructions to the harness from outside the VM to agent(s) installed inside. Ideally there is no Codex/Claude/etc. installed on the host.

You can do exactly that with coderunner

https://GitHub.com/instavm/coderunner

Nice! I will be sure to check it out. IMHO it's a good thing if there's a bit of competition.