Function install_to_cache 

pub fn install_to_cache(
    archive_path: &Path,
    writable_mem_names: &[&str],
) -> Result<CacheInstallOutcome, InstallError>

Validate an archive and land it in the global content-addressed cache — the cache-side half of memstead install, with no config or mount side effects (the caller registers the returned archive as a workspace-level read-only mount). Shares the validator, the shadow-name gate, and the content-addressed atomic-rename write with the historical combined path.