Use original task's start_date if a task continues after deferral (…

…#20062)

GitOrigin-RevId: 5cc5f434d745452651bca76ba6d2406167b7e2b9

airflow/models/taskinstance.py

@@ -1207,7 +1207,8 @@ def check_and_change_state_before_execution(
             # Attempt 0 for the first attempt).
             # Set the task start date. In case it was re-scheduled use the initial
             # start date that is recorded in task_reschedule table
-            self.start_date = timezone.utcnow()
+            # If the task continues after being deferred (next_method is set), use the original start_date
+            self.start_date = self.start_date if self.next_method else timezone.utcnow()
             if self.state == State.UP_FOR_RESCHEDULE:
                 task_reschedule: TR = TR.query_for_task_instance(self, session=session).first()
                 if task_reschedule:
@@ -1533,6 +1534,8 @@ def _defer_task(self, session, defer: TaskDeferred):
         session.flush()
 
         # Then, update ourselves so it matches the deferral request
+        # Keep an eye on the logic in `check_and_change_state_before_execution()`
+        # depending on self.next_method semantics
         self.state = State.DEFERRED
         self.trigger_id = trigger_row.id
         self.next_method = defer.method_name