I'm not sure I understand you problem. In CGI::App, the error is passed as a parameter to your error runmode:

sub error {
    my $self = shift;
    my $error = shift;
    
    # Do something with the error - e.g. write it to a log file
    $self->logger->error("Warning error: $error");
    
    #.... and then provide friendly message to user
}
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