smolmachines / smolvm as a sandbox for untrusted Python & JavaScript

Per Simon Willison's Weblog, a researcher tasked Claude Fable 5 with exploring smolmachines, a sandbox for running untrusted Python and JavaScript code with strict resource limits—CPU, RAM, and no network access, designed for tasks like data transformation. The snag: Claude Code's web environment runs inside a Firecracker guest without access to nested virtualization, so the sandbox itself couldn't launch. The solution was direct—GitHub Actions Ubuntu runners do expose the required virtualization features, so the real tests ran there instead on a temporary branch.

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