smolmachines / smolvm as a sandbox for untrusted Python & JavaScript
Claude Fable 5 autonomously pivoted to GitHub Actions when local sandbox lacked KVM support
“This Claude Code container: Linux 6.18.5-fc-v20 (itself a Firecracker guest), 4 vCPU, 15GB RAM. No /dev/kvm, no vmx/svm CPU flags → no nested virt.”
Simon Willison tasked Claude Fable 5 with evaluating smolmachines/smolvm as a secure sandbox for untrusted code execution, but the Claude Code for web environment lacked KVM support needed to run the tool. Fable independently devised a Plan B: creating a temporary GitHub Actions workflow on a branch to run the test battery in a KVM-capable runner, then collecting the logs. This is a concrete demonstration of Fable's 'relentlessly proactive' agentic reasoning — self-diagnosing environmental constraints and finding an alternative execution path without human intervention.