sub add_client {
    my( $db, $rec, $opt, @bad ) = @_;
    $opt ||= {};
    my $uniq = delete $opt->{require_unique} || 0;
    my $fatal = delete $opt->{fail_fatal} // ! $uniq;
    my $contract = delete $opt->{contract};
    my $context = _context( delete $opt->{referrer} );
    argue( \$opt, \@bad, { db => $db, rec => $rec } );