Error handling for processes

We would like NF to support metadata tracking and routing; this would for example enable a process to inform another process that an action was not taken or a stage not passed, this could trigger other tasks. I include two examples from our current pipeline below; perhaps not a perfect match, but they informed my initial thinking about this.

    process irods {
        tag "${samplename}"

        input:
            val samplename from sample_list.flatMap{ it.readLines() }

        output:
            set val(samplename), file('*.cram') optional true into ch_cram_files
            file('*.lostcause.txt') optional true into ch_lostcause_irods

        script:
        """
        if bash -euo pipefail irods.sh -t ${params.studyid} -s ${samplename}; then
          true
        else
          stat=\$?
          tag='UNKNOWN'
          if [[ \$stat == 64 ]]; then tag='nofiles'; fi
          echo -e "${samplename}\\tirods\\t\$tag" > ${samplename}.lostcause.txt
        fi
        """
   }

# later ...
    ch_star_accept = Channel.create()
    ch_star_reject = Channel.create()

    star_aligned
        .choice(ch_star_accept, ch_star_reject)
            { namelogsbams -> check_log(namelogsbams[1]) ? 0 : 1 }

    ch_star_accept
    .map    { name, logs, bams -> [name, bams] }
    .into   { ch_featurecounts; ch_indexbam }

    ch_star_reject
    .map    { it -> "${it[0]}\tSTAR\tlowmapping\n" }
    .mix(ch_lostcause_irods)
    .set    { ch_lostcause }

The issue provides Groovy process and channel examples but names no files or tests. Start by tracing the existing process-failure and channel-routing behavior, then clarify the metadata model and acceptance cases with maintainers. Done would require an agreed design and tests covering process status propagation and routing.