Earendil's own Gondolin tool is the best sandboxing model I've found so far. It just executes the toolcalls in a minimal ephemeral VM, unlike most others which run the whole harness inside the sandbox. It's a bit rough around the edges (doesn't play well with other plugins and doesn't work under Bun), but it's great if you're willing to put in some effort to tweak your setup. Much more comforting to fire off long-running parallel tasks when you know the blast radius is fully contained lol.