It seems to me that there is some indirection happening here, so I took your Master.pl and tested it against some of my favorite modules:

indirect
Devel::SummarizedWarnings
Devel::SimpleTrace

#!/usr/bin/perl -l

use warnings;
use strict 'refs';
require qw(slave);

no indirect 'fatal';
use Devel::SimpleTrace;
use Devel::SummarizedWarnings;

$slave::typo = "Hello, World!";
warn $slave;
print 
  pop(@Devel::SummarizedWarnings::LOGGED_WARNINGS) =~ /$slave/;
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