Function fetch_catalog_models 

pub async fn fetch_catalog_models(
    client: &Client,
    provider_key: &str,
    overrides: &BTreeMap<String, String>,
) -> Result<Vec<CatalogModel>, String>

Fetch catalog models for any registered provider. OpenRouter uses its rich parser; all others use the generic parser. Compatible shim: callers that previously used registry::fetch_provider_models and then mapped to ExpandedModelEntry can switch to this.