Use logging.exception() to include stacktrace

When an exception has been caught, favor `exception` over `error`, since
`exception()` automatically preserves the error context.

pyproject.toml

@@ -111,7 +111,6 @@ ignore = [
   "SIM105",   # Use `contextlib.suppress`
   "SIM117",   # Avoid repeated `with` statements
   "TRY200",   # Use `raise from` to preserve context (also see B904)
-  "TRY400",   # Use logging.exception, not logging.error
 ]
 
 # By default, `ruff` will respect `.gitignore`

ws/signals/signup_signals.py

@@ -113,7 +113,7 @@ def revoke_existing_task(sender, instance, raw, using, update_fields, **kwargs):
             app.control.revoke(trip.lottery_task_id)
         except OperationalError:
             # Log the exception, but don't raise exceptions, preventing trip saving
-            logger.error("Failed to revoke lottery task for trip %s", trip.pk)
+            logger.exception("Failed to revoke lottery task for trip %s", trip.pk)
         else:
             instance.lottery_task_id = None
 
@@ -135,7 +135,7 @@ def add_lottery_task(sender, instance, created, raw, using, update_fields, **kwa
     try:
         task_id = tasks.run_lottery.apply_async((trip.pk,), eta=trip.signups_close_at)
     except OperationalError:
-        logger.error("Failed to make lottery task for trip %s", trip.pk)
+        logger.exception("Failed to make lottery task for trip %s", trip.pk)
     else:
         trip.lottery_task_id = task_id
         # Use update() to avoid repeated signal on post_save

ws/views/participant.py

@@ -173,7 +173,7 @@ def post(self, request, *args, **kwargs):
                 try:
                     tasks.update_participant_affiliation.delay(participant.pk)
                 except OperationalError:
-                    logger.error(
+                    logger.exception(
                         "Unable to update affiliation to %s for participant %s",
                         participant.pk,
                         participant.affiliation,