And B::Deparse confirms what ikegami and chromatic say above (which is what I should have checked in the first place):

$ perl -MO=Deparse tst
my $i = 0;
main();
sub main {
    use warnings;
    use strict 'refs';
    print "${i}: main()\n";
    exit if $i++ > 10;
    print "Calling foo()\n";
    foo();
}
sub foo {
    use warnings;
    use strict 'refs';
    print "foo()\n";
    return unless my $fn = main()->can('bar');
    print "We can bar\n";
    &$fn();
}
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