Function export_metadata 

pub fn export_metadata(
    trace_log: &Path,
    id: &str,
    output: &Path,
) -> Result<MetadataExportStats, ExportError>

Export all records whose turn_id or request_id equals id from the trace JSONL at trace_log into a fresh private file at output.

F5 hardening: the log is streamed line by line under explicit per-line (1 MiB) and total (64 MiB) byte bounds — no unbounded whole-file read — and parse failures are reported by static category and position only, never by echoing persisted bytes.