refactor: document cronNotAfter for exam closure

src/Jobs/Crontab.hs

@@ -365,6 +365,10 @@ determineCrontab = execWriterT $ do
 
       case closeTime of
         Just close -> do
+          -- If an exam that was previously under `ExamCloseSeparate` rules transitions to `ExamCloseOnFinish`, it might suddenly have been closed an arbitrary time ago
+          -- If `cronNotAfter` was only `appNotificationExpiration` in that case, no notification might ever be sent
+          -- That's probably fine.
+
           changedResults <- lift . E.select . E.from $ \examResult -> do
             E.where_ $ examResult E.^. ExamResultExam E.==. E.val nExam
                  E.&&. examResult E.^. ExamResultLastChanged E.>. E.val close