I've taken to sandboxing my entire agent in a Docker container. I wrote a tool that pretends to be an ACP client but is actually making Docker containers, copying files I specified in, bind-mounting, etc, and then proxying ACP via websocket to an agent in the container (except the ACP terminal/FS commands, those happen in the container).

It works well, though there is some leakiness around paths. I opted to make it place/mount files at the same path as on the host so paths are the same (as opposed to manipulating the ACP messages to modify paths on the fly, that felt messy and buggy).

Configurable networking is on my list for the future, but I haven't decided whether to start with IP-level firewalls or if it's better to start with a proxy and firewall rules to force traffic to it. IP firewalls suck for APIs that might have semi-dynamic IPs.

[1] https://github.com/SethCurry/abyss