Function write_captured_record 

pub fn write_captured_record(
    directory: &Path,
    record: &CapturedRecord,
) -> Result<(), CaptureOrderError>

What: Writes captured.json exclusively and makes it durable. Why: A transaction directory holds one captured record, and a second write means a bug, so the exclusive open refuses it.

In TS you’d write (pseudocode):

await writeCapturedRecord({ directory, record });