Function enumerate_sibling_instances 

pub fn enumerate_sibling_instances(
    channels_root: &Path,
    own_channel: &str,
    own_version: &str,
) -> Vec<SiblingInstance>

Walk <channels_root>/*/versions/*/ and return every (channel, version) pair other than (own_channel, own_version).

Pure filesystem read — read_dir only, no pipe/socket contact, no writes. Best-effort: a missing or unreadable channels_root (fresh install, permissions issue) yields an empty list rather than an error.