feat: sync latest ARR implementation

tests/test_monthly_reports_core.py

@@ -78,7 +78,7 @@ class MonthlyReportsCoreTests(unittest.TestCase):
         report = build_monthly_report(
             2026,
             7,
-            date(2026, 7, 26),
+            date(2026, 7, 2),
             snapshot(
                 fact(2, channel="T- HANATOUR TD CO., L"),
                 fact(1),
@@ -92,13 +92,13 @@ class MonthlyReportsCoreTests(unittest.TestCase):
         )
         self.assertEqual(report.row_count, 2)
         self.assertEqual(report.channel_manifest[-1], ("T- HANATOUR TD CO., L", 6, 1))
-        self.assertEqual(report.filename, "各渠道情况-2026年07月-更新至7.26.xlsx")
+        self.assertEqual(report.filename, "各渠道情况-2026年07月-更新至7.2.xlsx")
 
     def test_kb_payload_has_extra_typed_amount(self):
         report = build_monthly_report(
             2026,
             7,
-            date(2026, 7, 26),
+            date(2026, 7, 2),
             snapshot(fact(1, channel="DY-AI-Easy-KB", rooms=2)),
         )
 
@@ -122,6 +122,18 @@ class MonthlyReportsCoreTests(unittest.TestCase):
         self.assertEqual(report.row_count, 0)
         self.assertEqual(report.daily_versions[0].daily_version_id, 126)
 
+    def test_nonempty_report_rejects_as_of_after_greatest_arrival(self):
+        with self.assertRaises(MonthlyReportError) as caught:
+            build_monthly_report(
+                2026,
+                7,
+                date(2026, 7, 30),
+                snapshot(fact(1, business_date=date(2026, 7, 27))),
+            )
+
+        self.assertEqual(caught.exception.code, ErrorCode.SOURCE_INVALID)
+        self.assertIn("greatest included ARRIVAL", caught.exception.safe_message)
+
     def test_mismatched_metric_or_pin_is_rejected(self):
         source = fact(1)
         cases = (