Function write_captured_record 

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

What: Writes captured.json exclusively and whole, without syncing it. Why: A transaction directory holds one captured record, and a second write means a bug, so the exclusive open refuses it. A torn or lost record only costs a warning and subsumption in later replays (the tearing table in doc/planning/cli-git-spawn-and-sync-reduction.md), so no flush is worth waiting for.

In TS you’d write (pseudocode):

await writeCapturedRecord({ directory, record });