Ahh, refactoring. It reminds me of the days of Transport Tycoon when you're trying to find the right track combination that's both elegant and efficient. In this case, I think a whole lot of fuss can be trimmed right out, which in track terms means less money and faster transport. In programmatic terms, simpler can, to a point, mean fewer bugs, since the code is much more concise.

What about this idiomatic solution?

!$history{$_}++ && splice(@history, $i--, 1);

Or even better, ditch that awful for-loop:

my %seen;
@history = reverse grep { !$seen{$_}++ } reverse @history;
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