docs: Update Celery code owner ADR with failed attempt

edx_django_utils/monitoring/docs/decisions/0003-code-owner-for-celery-tasks.rst

@@ -24,13 +24,20 @@ Consequences
 ------------
 
 * We added the new decorator as needed for all existing tasks.
-* New celery tasks will need to add the same decorator. See "Rejected Alternatives" for a potential alternative.
+* New celery tasks will need to add the same decorator.
 
 (Rejected) Alternatives
 -----------------------
 
-An untested potential alternative to the ``@set_code_owner_attribute`` decorator is to try celery's `task_prerun signal`_ in an IDA, which would also ensure all future celery tasks are automatically handled. Although this is a potentially superior solution, it was missed at the time of implementation. We will not be switching to this solution at this time given we have a working solution and other priorities, but it is a potentially viable solution if the need arises.
+Celery has a `task_prerun signal`_ that would allow us to execute code every time a task is about to start.
 
-Additionally, if this alternative solution were implemented, it would be best to not add celery as a dependency to this library, and to document a new edx-platform implementation. It is unlikely that the solution will be needed outside of edx-platform.
+This possibility was discovered after we had already annotated tasks. We hoped this would ensure all celery tasks were automatically handled rather than requiring explicit decorators. However, when we `trialed the task_prerun approach <https://github.com/openedx/edx-platform/pull/33180>`_ we discovered that no attribute was set on the Celery tasks. This seems to be because New Relic instruments the task function itself with transaction-start and transaction-end calls, so any signals that are run before or after the task execution occur outside the scope of the transaction.
+
+Theoretically, we could do something similar to New Relic's monkeypatching in order to inject a code owner attribute call, but this would be fragile and could lead to disruptive failures.
 
 .. _task_prerun signal: https://docs.celeryproject.org/en/stable/userguide/signals.html#task-prerun
+
+Changelog
+---------
+
+* 2023-09-19: Updated ``task_prerun`` alternative with results of a failed attempt at using it.