anchor.diff:  intercept(#'queue.purge'{queue = QName} = Method, VHost) ->
       case is_sharded(VHost, QName) of
           true ->
  -            {error, format("Can't purge sharded queue: ~p", [QName])};
  +            precondition_failed("Can't purge sharded queue: ~p", [QName]);
           _    ->
               {ok, Method}
       end.
  
positive.code: intercept(#'queue.declare'{queue = QName} = Method, VHost) ->
      case is_sharded(VHost, QName) of
          true ->
              {error, format("Can't declare sharded queue: ~p", [QName])};
          _    ->
              {ok, Method}
      end;
  
negative.code:         {ok, QName2} ->
              {ok, Method#'basic.consume'{queue = QName2}};
          {error, QName} ->
              precondition_failed("Error finding sharded queue for: ~p", [QName])
      end;
  
  intercept(#'basic.get'{queue = QName} = Method, VHost) ->
  