Function append_event_log 

async fn append_event_log(
    ctx: &ApplierCtx<'_>,
    ts: DateTime<Utc>,
    host_id: Option<&str>,
    rollout_id: Option<&str>,
    kind: EventLogKind,
    payload: Value,
)

Send an entry to the bounded MPSC drained by super::event_log_writer. Backpressure (full channel) blocks the caller via await — that’s the desired propagation per the audit-log no-fail-open contract.

If the writer task has died (closed channel), log + return rather than panic — the runtime is being torn down and losing a few tail entries is acceptable.