Function list_production_clusters 

pub(super) async fn list_production_clusters(
    client: &Client,
) -> Result<Vec<ProductionClusterRecord>, ConnectionError>

List clusters that host at least one promoted deployment.

For each such cluster, returns one representative protected deployment (the most recently promoted one) so callers can explain why the cluster is classified production. Used by dev to refuse overlay deployments that would land on production compute.