Problems with "call()" in the PEngines sandbox?

Help!
1

I’m using: SWI-Prolog version 8.0.2 on Ubuntu Linux 18.04.

In the code below, you can see a function I created named my_apply/2 to apply a Goal to a list of arguments. This code works fine when I test it outside of PEngines in the SWI-Prolog console. However, when I pass the exact same code in the src_text parameter during the creation of a PEngines instance, I get the following error back:

Sandbox restriction!
Could not derive which predicate may be called from
  call(C)
  '329664db-065f-4c7d-9744-cc0db034997e':my_apply_1(u_assert(item_state(A,locked)),B)
  '329664db-065f-4c7d-9744-cc0db034997e':my_apply(u_assert(item_state(A,locked)),B)
  '329664db-065f-4c7d-9744-cc0db034997e':initialize_game

As you can also see in the code below during the initialize_game/0 predicate, the predicate named u_assert() that I am using in the call to my_apply() works fine when not being passed to my_apply(). So I assume it must be something to do with trying to execute the predicate via the call() method while in the PEngines sandbox, as the error indicates?

NOTE: The error occurs during the creation of the PEngines instance, not during a call to ask(). It happens when the code I pass via src_text executes some initialization code.

How can I get this working?

Here is the relevant code from the code I pass in the src_text parameter during the creation of my PEngines instance:

% ----->>>>> u_assert/u_retract/u_retractall

% This predicate asserts an element of user data.
u_assert(UData) :-
	nonvar(UData),
	!,
	assert(user_data(UData)).

%	Handle assert or retract with goal with var() first argument.
apply_build_new_goal(OuterGoal, ListElement, Goal_2) :-
	nonvar(OuterGoal),
	nonvar(ListElement),
	OuterGoal =.. [ OuterPredName, InnerGoal | OuterArgs],
	member(OuterPredName,
	    [
	        assert,
	        retract,
	        u_assert,
	        u_retract
	    ]),
	nonvar(InnerGoal),
	InnerGoal =.. [ InnerPredName, InnerFirstArg | InnerArgs ],
	nonvar(InnerPredName),
	var(InnerFirstArg),
	!,
	% Build the new inner goal with the list element given.
	InnerGoal_2 =.. [ InnerPredName, ListElement | InnerArgs],
	% Build the new outer goal.
	Goal_2 =.. [ OuterPredName, InnerGoal_2 | OuterArgs].

%	Handle plain goal with var() first argument..
apply_build_new_goal(Goal, ListElement, Goal_2) :-
	nonvar(Goal),
	nonvar(ListElement),
	Goal =.. [ PredName, FirstArg | Args ],
	nonvar(PredName),
	var(FirstArg),
	!,
	Goal_2 =.. [ PredName, ListElement | Args].

% my_apply_1 iterates the list of elements to apply the given goal to.
my_apply_1(_, []) :- !.
my_apply_1(Goal, [H | T]) :-
	!,
	% Build the new goal using the current list element to act upon.
	apply_build_new_goal(Goal, H, Goal_2),
	% Apply the new goal.
	call(Goal_2),
	% Continue.
	my_apply_1(Goal, T).

% Apply the given Goal to each element in the given list.
my_apply(Goal, TargetList) :-
	nonvar(Goal),
	nonvar(TargetList),
	my_apply_1(Goal, TargetList).

This is the code that resides in the code passed via src_text that “auto-runs” when the PEngine instance is created. The error happens during the call to my_apply():

initialize_game :-
    pengine_output('INITIALIZING GAME!'),
    u_assert(inventory(player_1, pork)),
    % Lock ALL the rooms.
    my_apply(u_assert(item_state(_, locked)), RoomList),