Hey! Rivet includes a library for running untrusted user code called agentOS: https://rivet.dev/agentos/

It provides Linux-compatible sandboxing using V8 / WebAssembly. Supports full POSIX filesystems, networking stacks, and process trees. Security-wise, it's the same model as Cloudflare Workers & Chromium.

Rivet is frequently used for running the harness outside of the sandbox. Wrote a bit about why here: https://rivet.dev/blog/2026-07-27-run-your-harness-outside-t...