Function diff_items 

pub fn diff_items(
    catalog_name: &str,
    local_hashes: &HashMap<String, String>,
    remote_hashes: &HashMap<String, String>,
) -> CatalogItemsDiff

Diff catalog items by comparing their content hashes. Only the hash maps are needed — the actual row data is not loaded or compared.

catalog_name is passed explicitly so the caller controls which name appears in the diff — the local map may be empty when the catalog only exists remotely.

Output id lists are sorted for deterministic display and test assertions.