chore: sync GovOPlaN module split state

tests/test_ical.py

@@ -92,6 +92,7 @@ END:VCALENDAR
         self.assertEqual(event["start_at"], datetime(2026, 7, 8, 7, 0, tzinfo=timezone.utc))
         self.assertEqual(event["end_at"], datetime(2026, 7, 8, 8, 30, tzinfo=timezone.utc))
         self.assertEqual(event["duration_seconds"], 5400)
+        self.assertTrue(event["icalendar"]["standard"]["uses_duration"])
         self.assertEqual(event["description"], "Line one\nLine two")
         self.assertEqual(event["location"], "Room; 1")
         self.assertEqual(event["timezone"], "Europe/Berlin")
@@ -164,6 +165,38 @@ END:VCALENDAR
         self.assertIn("BEGIN:VALARM", ics)
         self.assertIn("TRIGGER:-PT15M", ics)
 
+    def test_generated_ics_preserves_duration_when_source_used_duration(self) -> None:
+        event = SimpleNamespace(
+            uid="event-duration@example.test",
+            start_at=datetime(2026, 7, 8, 7, 0, tzinfo=timezone.utc),
+            end_at=datetime(2026, 7, 8, 8, 30, tzinfo=timezone.utc),
+            duration_seconds=5400,
+            all_day=False,
+            timezone="Europe/Berlin",
+            summary="Duration",
+            sequence=0,
+            status="CONFIRMED",
+            transparency="OPAQUE",
+            classification="PUBLIC",
+            description=None,
+            location=None,
+            categories=[],
+            rrule=None,
+            organizer=None,
+            attendees=[],
+            rdate=[],
+            exdate=[],
+            reminders=[],
+            attachments=[],
+            related_to=[],
+            icalendar={"standard": {"uses_duration": True}},
+        )
+
+        ics = event_to_ics(event)
+
+        self.assertIn("DURATION:PT1H30M", ics)
+        self.assertNotIn("DTEND", ics)
+
     def test_expand_event_occurrences_applies_rrule_rdate_and_exdate(self) -> None:
         parsed = parse_vevent(
             """BEGIN:VCALENDAR