How I got rid of term_variables/3 (Was: 50 Years of Prolog Nonsense)

It all began with the bagof/3 choker:
test :-
    bagof(X, N^(between(1,300,X), between(1,300,N),
       length(_,N)), _), fail; true.
Which makes Prolog system tumble:
/* SWI-Prolog 9.3.14 */
?- time(test).
Action (h for help) ? abort
% 468,739 inferences, 52.016 CPU in 53.069 seconds (98% CPU, 9012 Lips)
Execution Aborted
/* Scryer Prolog 0.9.4-201 */
?- time(test).
^C   % CPU time: 110.153s, 145_508_466 inferences
    error('$interrupt_thrown',repl/0).
Its mostlikely the same old problem that was
observed years ago, in that the canonicalization
of variables before the keysort/2 creates long
instantiation chains. It can be solved by adjusting
the unification order. Here is a take in Dogelog Player:
/* Dogelog Player 1.2.5 */
?- time(test).
% Zeit 7405 ms, GC 21 ms, Lips 3962971, Uhr 10.11.2024 00:57
true.