The problem:

my @fields = qw(
    opffile
    spec
    twig
    twigroot
    twigmeta
    error
    );               # This stmt is only executed once
                     # the whole file is compiled.
    
use fields @fields;  # This line is executed as soon
                     # as it is compiled.
[download]

Workaround:

my @fields;

BEGIN {
    @fields = qw(
        opffile
        spec
        twig
        twigroot
        twigmeta
        error
    );
}                    # This block is executed as soon
                     # as this line is compiled.

use fields @fields;  # This line is executed as soon
                     # as it is compiled.
[download]