Function record_subscription_event 

pub fn record_subscription_event(
    db_path: &Path,
    sub_id: &str,
    correlation_id: &str,
    event_type: &str,
    payload: &str,
) -> Result<()>

v0.7.0 K6 — append a subscription_events audit row for one outgoing delivery. Called from the dispatch worker BEFORE the network send so replay-from-cursor (K7) sees a stable record even if the dispatcher process crashes mid-retry. The row is created with delivery_status = 'pending'; [update_event_status] transitions it to 'ack' / 'failed' once the retry ladder settles.