fix(security): neutraliser le contexte des erreurs expurgées

pronote_sync/pipeline/steps/fetch.py

@@ -121,6 +121,7 @@ def fetch_step(
     :raises PronoteAuthRotationError: Si une rotation du token d'authentification
         pronotepy est nécessaire : propagée telle quelle jusqu'au pipeline.
     """
+    critical_error: PipelineCriticalError | None = None
     try:
         lessons, school_events = fetcher.fetch_agenda()
         target_date = resolve_target_date(today or date.today(), lessons, school_events)
@@ -130,9 +131,11 @@ def fetch_step(
     except PronoteAuthRotationError:
         raise
     except Exception as exc:
-        raise PipelineCriticalError(
+        critical_error = PipelineCriticalError(
             f"Récupération Pronote impossible : {redact_exception(exc)}", step="fetch"
-        ) from None
+        )
+    if critical_error is not None:
+        raise critical_error from None
 
     messages, warnings = _fetch_optional_messages(fetcher)
     return (