fix(cron): use elapsed time across daylight-saving transitions (#671)

* fix(cron): use elapsed time across daylight-saving transitions

* fix(cron): preserve local-time delays during DST rollback

---------

Co-authored-by: jinli.yl <jinli.yl@alibaba-inc.com>

reme/components/job/cron_job.py

@@ -32,7 +32,9 @@ class CronJob(BackgroundJob):
         from croniter import croniter
 
         nxt = croniter(self.cron_expr, now).get_next(datetime.datetime)
-        return max(0.0, (nxt - now).total_seconds())
+        # croniter may reset fold on naive local times, so retain their wall-clock arithmetic.
+        delay = nxt.timestamp() - now.timestamp() if tz_name else (nxt - now).total_seconds()
+        return max(0.0, delay)
 
     async def _execute_steps(self) -> Response:
         context = RuntimeContext(stop_event=self._stop_event, **self.kwargs)

tests/unit/test_cron_delay.py

@@ -0,0 +1,66 @@
+"""Cron waits use elapsed seconds across timezone offset changes."""
+
+# pylint: disable=protected-access,missing-function-docstring,missing-class-docstring
+
+import datetime
+import time
+from types import SimpleNamespace
+
+import pytest
+
+from reme.components.job import cron_job as cron_job_module
+from reme.components.job.cron_job import CronJob
+
+
+@pytest.mark.parametrize(
+    "timezone,instant,expected_delay",
+    [
+        ("America/New_York", "2026-03-08T06:30:00+00:00", 1800),
+        ("America/New_York", "2026-11-01T04:30:00+00:00", 12600),
+        ("Europe/London", "2026-03-29T00:30:00+00:00", 5400),
+        ("Europe/London", "2026-10-25T00:30:00+00:00", 9000),
+        ("Australia/Lord_Howe", "2026-10-03T15:00:00+00:00", 3600),
+        ("Australia/Lord_Howe", "2026-04-04T13:30:00+00:00", 10800),
+        ("America/New_York", "2026-01-15T06:30:00+00:00", 5400),
+        ("Asia/Shanghai", "2026-03-07T17:30:00+00:00", 5400),
+        (None, "2026-01-15T01:30:00+00:00", 5400),
+    ],
+)
+def test_cron_delay_uses_elapsed_seconds(monkeypatch, timezone, instant, expected_delay):
+    fixed = datetime.datetime.fromisoformat(instant)
+
+    class FixedDatetime(datetime.datetime):
+        @classmethod
+        def now(cls, tz=None):
+            return fixed.astimezone(tz) if tz else fixed.replace(tzinfo=None)
+
+    monkeypatch.setattr(cron_job_module, "datetime", SimpleNamespace(datetime=FixedDatetime))
+    job = CronJob(cron="0 3 * * *")
+    job.app_context = SimpleNamespace(app_config=SimpleNamespace(timezone=timezone))
+
+    assert job._next_fire_delay() == expected_delay
+
+
+@pytest.mark.skipif(not hasattr(time, "tzset"), reason="requires time.tzset")
+@pytest.mark.parametrize("with_app_context", [True, False], ids=["local-timezone", "standalone"])
+def test_cron_local_time_after_dst_fallback(monkeypatch, with_app_context):
+    fixed = datetime.datetime.fromisoformat("2026-11-01T06:30:00+00:00")
+
+    class FixedDatetime(datetime.datetime):
+        @classmethod
+        def now(cls, tz=None):
+            return datetime.datetime.fromtimestamp(fixed.timestamp(), tz)
+
+    try:
+        with monkeypatch.context() as patch:
+            patch.setenv("TZ", "America/New_York")
+            time.tzset()
+            patch.setattr(cron_job_module, "datetime", SimpleNamespace(datetime=FixedDatetime))
+            job = CronJob(cron="* * * * *")
+            if with_app_context:
+                job.app_context = SimpleNamespace(app_config=SimpleNamespace(timezone=None))
+
+            assert FixedDatetime.now().fold == 1
+            assert job._next_fire_delay() == 60
+    finally:
+        time.tzset()