fix(cron): prevent duplicate fires when multiple jobs trigger simultaneously (#14256)

The `computeNextRunAtMs` function used `nowSecondMs - 1` as the
reference time for croner's `nextRun()`, which caused it to return the
current second as a valid next-run time. When a job fired at e.g.
11:00:00.500, computing the next run still yielded 11:00:00.000 (same
second, already elapsed), causing the scheduler to immediately re-fire
the job in a tight loop (15-21x observed in the wild).

Fix: use `nowSecondMs` directly (no `-1` lookback) and change the
return guard from `>=` to `>` so next-run is always strictly after
the current second.

Fixes #14164

src/cron/schedule.test.ts

@@ -39,22 +39,22 @@ describe("cron schedule", () => {
     const dailyNoon = { kind: "cron" as const, expr: "0 0 12 * * *", tz: "UTC" };
     const noonMs = Date.parse("2026-02-08T12:00:00.000Z");
 
-    it("returns current occurrence when nowMs is exactly at the match", () => {
+    it("advances past current second when nowMs is exactly at the match", () => {
+      // Fix #14164: must NOT return the current second — that caused infinite
+      // re-fires when multiple jobs triggered simultaneously.
       const next = computeNextRunAtMs(dailyNoon, noonMs);
-      expect(next).toBe(noonMs);
+      expect(next).toBe(noonMs + 86_400_000); // next day
     });
 
-    it("returns current occurrence when nowMs is mid-second (.500) within the match", () => {
-      // This is the core regression: without the second-floor fix, a 1ms
-      // lookback from 12:00:00.499 still lands inside the matching second,
-      // causing croner to skip to the *next day*.
+    it("advances past current second when nowMs is mid-second (.500) within the match", () => {
+      // Fix #14164: returning the current second caused rapid duplicate fires.
       const next = computeNextRunAtMs(dailyNoon, noonMs + 500);
-      expect(next).toBe(noonMs);
+      expect(next).toBe(noonMs + 86_400_000); // next day
     });
 
-    it("returns current occurrence when nowMs is late in the matching second (.999)", () => {
+    it("advances past current second when nowMs is late in the matching second (.999)", () => {
       const next = computeNextRunAtMs(dailyNoon, noonMs + 999);
-      expect(next).toBe(noonMs);
+      expect(next).toBe(noonMs + 86_400_000); // next day
     });
 
     it("advances to next day once the matching second is fully past", () => {