fix(backend): ULID使用時にnotificationTimelineへのXADDが失敗し続け、通知が約10秒遅延する問題を修正 (#17358)

packages/backend/test/unit/misc/ulid.ts

@@ -38,4 +38,12 @@ describe('misc:ulid', () => {
 		// id[16] = Z
 		expect(() => parseUlidFull('01KPS7S300ABCDEFZ000000000')).not.toThrow();
 	});
+
+	test('parseUlidFull - additional exceeds uint64 max (all-Z randomness)', () => {
+		// All 16 random chars = 'Z' (Crockford max) → 80-bit value > uint64 max
+		const { additional } = parseUlidFull('01ARZ3NDEKZZZZZZZZZZZZZZZZ');
+		const uint64Max = 2n ** 64n - 1n;
+		expect(additional > uint64Max).toBe(true);
+		expect(BigInt.asUintN(64, additional) <= uint64Max).toBe(true);
+	});
 });