Nodebox's light runtime makes it easy to run in the browser, but the same guard rails matter once you start wiring it into agent workflows. We wrap every plan in connectors+watchers: each connector expects {status:'ok'}, logs sessionId, and watches retries/costs, and when we see 3+ retries or a cost bump above 2x baseline the run pauses, streams the guard log to a manual gate, and waits for a human to approve the diff before resuming. That pattern keeps generated previews predictable when agents spin up Express/Vite runs inside a tiny client-side container.