Function build_log_line 

pub fn build_log_line(
    desc: &str,
    err: &DataFusionError,
    query_id: &str,
    plan: Option<&Arc<dyn ExecutionPlan>>,
) -> String

Builds the full server-side log line for a classified DataFusionError: desc, the error’s own Display (its outer Context chain intact, with backtrace if enabled – unlike find_root(), which is for classification only), the query_id, and – when there’s no diagnostic span to show the caller instead – the truncated physical plan text. pub so tests can assert its content, including the truncation marker, without capturing log output.