write / read / read_bytes / list / remove / rename / mkdir / exists.
remove is recursive; write creates parent directories.
Sharp edges
4 MiB perwrite call (chunk bigger payloads), 16 MiB per read
(the exec output cap; read_bytes is base64 under the hood). For bulk data,
download inside the sandbox (sb.run("curl -O …")) instead of pushing it
through the API.