add jitter and tests

server/src/domain/jobs/job.repository.mongo.ts

@@ -88,9 +88,9 @@ class MongoJobsRepository implements IJobsRepository {
 
 		let nextScheduledAt = scheduledRunAt + intervalMs;
 
-		// If the job fell behind, skipped missed runs
+		// If the job fell behind, skip the missed runs. Spread the next run with jitter to avoid a herd
 		if (nextScheduledAt <= now) {
-			nextScheduledAt = now + intervalMs;
+			nextScheduledAt = now + intervalMs + Math.floor(Math.random() * intervalMs);
 		}
 
 		const res = await JobModel.updateOne(

server/test/integration/jobsRepository.test.ts

@@ -160,7 +160,7 @@ describe("MongoJobsRepository", () => {
 			expect(row?.runCount).toBe(5);
 		});
 
-		it("skips missed ticks when the worker has fallen behind", async () => {
+		it("skips missed ticks when the worker has fallen behind, with jitter to avoid a herd", async () => {
 			await seedJob({ lockedBy: ownedBy(repo), lockedUntil: NOW + LOCK_MS });
 
 			// scheduled NOW, interval 60s, but completion is 200s late → NOW+60s is already past
@@ -168,8 +168,10 @@ describe("MongoJobsRepository", () => {
 			await repo.recordSuccess("check:mon-1", NOW, 60_000, now);
 
 			const row = await readRow("check:mon-1");
-			// no catch-up burst: jump to the next aligned tick from now, not NOW+60_000
-			expect(row?.nextScheduledAt).toBe(now + 60_000);
+			// no catch-up burst: rebased to one interval from now, plus up to one interval of jitter
+			// so behind-jobs don't re-synchronize. Never earlier than now + interval (no over-checking).
+			expect(row?.nextScheduledAt).toBeGreaterThanOrEqual(now + 60_000);
+			expect(row?.nextScheduledAt).toBeLessThan(now + 120_000);
 		});
 
 		it("returns false for an unknown id", async () => {