Tip: Keep Agent Code-Execution State Resident With a MicroPython+WASM Sandbox, Then Red-Team the Sandbox

Simon Willison·medium signal

Simon Willison shipped datasette-agent-micropython, running agent-generated Python in a MicroPython+WASM sandbox where variables and functions stay resident across multiple execution calls — letting an agent build up and reuse state instead of restarting each turn. He then pinned a model at high reasoning effort and explicitly challenged it to break out of the sandbox (so far unsuccessfully), a concrete pattern for trusting agent code execution: prove the boundary holds before relying on it.