Function list_models_with_context_for 

pub async fn list_models_with_context_for(
    provider_key: &str,
) -> Result<Vec<(String, Option<usize>)>, Error>

Same listing as list_models_for, each id paired with the context window the catalog publishes for it. None means the catalog has no limit.context for that model — callers surface that as “unknown”, never as a default.