Idempotent: does nothing if images/busybox.tar already exists (your own
unofficial build, or a previous fetch). Otherwise tries skopeo, then
podman, then docker, in that order -- skopeo/podman both reliably produce
a genuine OCI Image Layout tar; a plain `docker save` only does if the
containerd image store happens to be enabled, so the result is verified
(oci-layout/index.json actually present at the tar root) regardless of
which tool produced it, falling through to the next option otherwise.
Clear instructions + nonzero exit if none of the three are available and
no fixture already exists.
Verified the no-op (already-present) path and the no-tools-available error
path directly (temporarily moved the existing images/busybox.tar aside and
back) -- this dev machine has none of skopeo/podman/docker installed, so
the actual fetch path itself is unverified here; the format-verification
step (looks_like_oci_layout()) is what protects against a `docker save`
that produced the legacy Docker tar format on some other machine.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gv3s5jckJKzh6JkMoi2Akz
