the default backend is a local git worktree. swap it via sandbox.backend in bernstein.yaml: docker (containerised), e2b (cloud sandbox), modal, blaxel, cloudflare workers sandboxes, daytona, runloop, vercel sandboxes. each is a plug-in implementing the sandboxbackend protocol in src/bernstein/core/sandbox/. install the matching extra (pip install "bernstein[e2b]", [modal], [cloudflare], ...). the orchestrator and adapters are unchanged; only the place where the agent's filesystem and process live changes. useful when you want hard isolation, or when the agent needs a different os than the orchestrator host.
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