GroupTxnSession.End: document no error is worth retrying
@@ -145,6 +145,9 @@ func (s *GroupTransactSession) Begin() error {
// in committing offsets fails, this aborts.
//
// This returns whether the transaction committed or any error that occurred.
+// No returned error is retriable. Either the transactional ID has entered a
+// failed state, or the client retried so much that the retry limit was hit,
+// and odds are you should not continue.
//
// Note that canceling the context will likely leave the client in an
// undesirable state, because canceling the context cancels in flight requests
