Fix midnight hour format to ensure "00" instead of "24"

src/lib/__tests__/hafas-time.test.ts

@@ -285,6 +285,19 @@ describe("hafasDateTime", () => {
       expect(time).toBe("000000000");
     });
 
+    it('produces "00" for midnight, not "24" (k-clock safety)', () => {
+      // Older ICU / Node can render midnight as "24" with hour: "numeric" + hour12: false.
+      // We use hour: "2-digit" which guarantees "00" through "23".
+      const utc = new Date(Date.UTC(2024, 0, 15, 0, 0, 0)); // Jan 15 00:00 UTC = Jan 15 01:00 CET
+      const { date: _date, time } = hafasDateTime(utc);
+      expect(time.startsWith("0")).toBe(true); // first digit is "0" from "01", never "24"
+
+      // Direct midnight in Vienna: Dec 31 23:00 UTC = Jan 1 00:00 CET
+      const midnightUtc = new Date(Date.UTC(2023, 11, 31, 23, 0, 0));
+      const { time: midnightTime } = hafasDateTime(midnightUtc);
+      expect(midnightTime).toBe("000000000");
+    });
+
     it("handles midnight wraparound (Vienna midnight is still previous UTC day)", () => {
       // Vienna Jan 1 00:00 CET = Dec 31 23:00 UTC
       const utc = new Date(Date.UTC(2023, 11, 31, 23, 0, 0));

src/lib/hafas-time.ts

@@ -14,7 +14,7 @@ function getTimezoneOffsetMinutes(instant: Date, tz: string): number {
   const getHour = (timeZone: string) => {
     const parts = new Intl.DateTimeFormat("en-US", {
       timeZone,
-      hour: "numeric",
+      hour: "2-digit",
       hour12: false,
     }).formatToParts(instant);
     return parseInt(parts.find((p) => p.type === "hour")!.value, 10);
@@ -79,7 +79,7 @@ function getDateTimeParts(instant: Date, tz: string) {
     year: "numeric",
     month: "numeric",
     day: "numeric",
-    hour: "numeric",
+    hour: "2-digit",
     minute: "numeric",
     second: "numeric",
     hour12: false,