sub isValidPath {
    my $path = shift;
    return system("nix-store --check-validity $path 2> /dev/null") == 0;
}

    if (system("nix-store --check-validity $outPath 2> /dev/null") != 0) {

    if (!isValidPath($outPath)) {

                die "missing input `$argName'" if !defined $inputInfo->{$argName};
                $extraArgs .= " --arg $argName '{path = " . $inputInfo->{$argName}->{storePath} . ";}'";

                my $storePath;
                if (defined $inputInfo->{$argName}) {
                    # The argument name matches an input.
                    $storePath = $inputInfo->{$argName}->{storePath};
                } else {
                    (my $prevBuild) = $db->resultset('Builds')->search(
                        {project => $project->name, jobset => $jobset->name, attrname => $argName},
                        {order_by => "timestamp DESC", rows => 1});
                    if (defined $prevBuild) {
                        # The argument name matches a previously built
                        # job in this jobset.  Pick the most recent
                        # build.  !!! refine the selection criteria:
                        # e.g., most recent successful build.
                        if (!isValidPath($prevBuild->outpath)) {
                            die "input path " . $prevBuild->outpath . " has been garbage-collected";
                        }
                        $storePath = $prevBuild->outpath;
                    } else {
                        # !!! reschedule?
                        die "missing input `$argName'";
                    }
                }
                $extraArgs .= " --arg $argName '{path = " . $storePath . ";}'";

        print "$extraArgs\n";