anchor.diff:          helper_handle:create(SessId, UserId, SpaceId, StorageDoc),
   
       case session:add_local_links(SessId, ?HELPER_HANDLES_TREE_ID,
  -        link_key(StorageId, SpaceId), HandleId
  +        make_link_name(StorageId, SpaceId), HandleId
       ) of
           ok ->
               {ok, HelperHandle};
  
positive.code:     {ok, helpers:helper_handle()} | {error, term()}.
  get_helper(SessId, SpaceId, StorageDoc, InCriticalSection) ->
      StorageId = storage:get_id(StorageDoc),
      FetchResult = case session:get_local_link(SessId,
          ?HELPER_HANDLES_TREE_ID, link_key(StorageId, SpaceId)) of
          {ok, [#link{target = Key}]} ->
              helper_handle:get(Key);
          {error, not_found} ->
  
negative.code: 
  -define(HELPER_HANDLES_TREE_ID, <<"helper_handles">>).
  
  % link name constructed from storage id and space id
  -type handle_link_name() :: datastore:link_name().
  
  %%%===================================================================
  %%% API
  %%%===================================================================
  