Function get_unique_nodes_for_data 

pub async fn get_unique_nodes_for_data(
    db: &DatabaseConnection,
    data_id: Uuid,
    dataset_id: Uuid,
) -> Result<Vec<GraphNode>, DatabaseError>

Return nodes belonging to (data_id, dataset_id) whose slug does NOT appear in any other row within the same dataset with a different data_id.

This is the Rust equivalent of Python’s shared-slug exclusion logic.