Function collapse_and_reindex 

fn collapse_and_reindex(
    identity_conn: &Connection,
    channel_mstore: Option<&Store>,
) -> Result<usize, String>

Collapse every group of global db_skills rows sharing a name (however large) to the earliest-created_at row (ties broken by id, for determinism), rewriting channel_mstore’s own ref rows (if given) and deleting the loser(s) from identity_conn’s db_skills — then swaps the uniqueness index. Returns the number of rows collapsed away.

Takes explicit connections/stores rather than resolving paths itself so it can be exercised directly in tests without depending on registry::resolve_identity_store_path’s env-var-driven resolution (the same reason m0031’s carry_skills/carry_mcp_servers take explicit Store params instead of opening their own).