pub fn require_tool(
name: &str,
install_hint: Option<&str>,
) -> Result<(), String>Expand description
Check that a CLI tool is available on PATH, returning a unified error
string otherwise. Before this helper, six if !command_available("X")
gates across oci.rs and cli/module.rs each produced a slightly
different “not found” message; strings had diverged in production. Pass
install_hint (a short imperative like “install it from https://…”)
to make the hint specific; None falls back to a generic “install it
or add it to PATH”.