test: verify realtime snapshots are fresh

tools/test_go_native_prod_smoke.py

@@ -140,6 +140,32 @@ class GoNativeProdSmokeTest(unittest.TestCase):
         self.assertEqual(check.status, "fail")
         self.assertIn("online=false", check.message)
 
+    def test_realtime_check_fails_when_snapshot_is_stale(self):
+        now = dt.datetime(2026, 7, 2, 0, 30, 0, tzinfo=dt.timezone.utc)
+
+        check = smoke.check_realtime(
+            "jt808.realtime",
+            {"vehicle_key": "JT808:013307811170", "updated_at_ms": 1782950400000},
+            max_age_minutes=15,
+            now=now,
+        )
+
+        self.assertEqual(check.status, "fail")
+        self.assertIn("updated_age_minutes=30.0", check.message)
+
+    def test_realtime_check_passes_when_snapshot_is_fresh(self):
+        now = dt.datetime(2026, 7, 2, 0, 30, 0, tzinfo=dt.timezone.utc)
+
+        check = smoke.check_realtime(
+            "jt808.realtime",
+            {"vehicle_key": "JT808:013307811170", "updated_at_ms": 1782951600000},
+            max_age_minutes=15,
+            now=now,
+        )
+
+        self.assertEqual(check.status, "pass")
+        self.assertIn("updated_age_minutes=10.0", check.message)
+
     def test_parse_tdengine_utc_timestamp_as_aware_utc(self):
         parsed = smoke.parse_tdengine_utc_timestamp("2026-07-01 17:36:02")