giveme git commit message 50 char

apps/edr-freight-api/src/modules/train-scheduling/booking-batch.constants.ts

@@ -31,6 +31,19 @@ export function paymentDrainMs(): number {
   );
 }
 
+/**
+ * ISO timestamp of the end of a pay window's drain tail, for client display
+ * (the "payment processing" countdown). Null in ⇒ null out.
+ */
+export function paymentDrainEndsAtIso(
+  deadline: Date | string | null | undefined,
+): string | null {
+  if (deadline == null) return null;
+  const ms = new Date(deadline).getTime();
+  if (!Number.isFinite(ms)) return null;
+  return new Date(ms + paymentDrainMs()).toISOString();
+}
+
 /**
  * A pay window AND its drain tail have closed.
  *