Cron: guard missing expr in schedule parsing

src/cron/schedule.test.ts

@@ -13,6 +13,18 @@ describe("cron schedule", () => {
     expect(next).toBe(Date.parse("2025-12-17T17:00:00.000Z"));
   });
 
+  it("throws a clear error when cron expr is missing at runtime", () => {
+    const nowMs = Date.parse("2025-12-13T00:00:00.000Z");
+    expect(() =>
+      computeNextRunAtMs(
+        {
+          kind: "cron",
+        } as unknown as { kind: "cron"; expr: string; tz?: string },
+        nowMs,
+      ),
+    ).toThrow("invalid cron schedule: expr is required");
+  });
+
   it("computes next run for every schedule", () => {
     const anchor = Date.parse("2025-12-13T00:00:00.000Z");
     const now = anchor + 10_000;