For example:
dcaro@toolsbeta-sgebastion-05:~$ toolforge build-show dcaro-buildpacks-pipelinerun-h2t88 ... Step: build - unknown({'container': 'step-build', 'imageID': 'docker-pullable://docker-registry.tools.wmflabs.org/toolforge-buster0-builder@sha256:70724160bd6c4ba38e750969d00aa69b4f032c3a5a20e140b25fbed5d054375f', 'name': 'build', 'terminated': {'containerID': 'docker://dd46fc5a11b2d70d0441ee0986dff9e53c9b60842c0e4d9c78cfaff0ded79d7a', 'exitCode': 0, 'finishedAt': '2022-04-04T10:41:10Z', 'reason': 'Completed', 'startedAt': '2022-04-04T10:40:22Z'}}) ...
This unkown string is being set in the _get_step_details_lines function.
https://gerrit.wikimedia.org/r/plugins/gitiles/cloud/toolforge/toolforge-cli/+/refs/heads/main/toolforge_cli/cli.py#113