Once you have a reference, it stays a reference until you dereference it. This is a bit clearer if you use a more accurate name for the function arguments.

Here's trimmed down version of your example, with names changed:

one(\%hash);

sub one {
    my($hashref) = @_;
    two($hashref);
}

sub two {
    my($hashref) = @_;  # it's still a hashref
    foreach ( keys %$hashref ) {
        print "$_\n";
    }
}
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