We needed hyper-lightweight sandboxes for massively parallel agent fanout that could be recycled in milliseconds, take only KBs of memory when not actively running a command, and can work with bottomless filesystems.

Tinysandbox is like just-bash, but supports a minimal secure JS runtime via QuickJS WASM, random file IO, VFS checkpoint and restore, and streaming IO for working with large files.

It's designed for super-lightweight agents that don't need full linux, but still need the emergent behavior of shell commands and script writing to complete their task.