Function ensure_local_bins 

pub fn ensure_local_bins(
    runner: &dyn ProcessRunner,
    release_tag: &str,
    version: &str,
    repo: &str,
    arch: BoxArch,
    bin_dir: Option<&Path>,
    cache_root: &Path,
) -> Result<LocalBins>

Resolve box binaries from --bin-dir or download+extract a Release tar.gz.

Errors

Returns crate::HortoError when paths are missing, download fails, or extract fails.