The set_pipeline step should unpause pipelines it archived when unarchiving them, or include a flag to do so

[Clockwork757]

We manage a few hundred generated pipelines that get set from one job. Recently due to an upstream change in our source of truth one of the generated pipelines was deleted, which archived it. After it was restored we didn't notice that it was paused for a while. We expected it to be unpaused like any other pipeline created via set_pipeline. I can't find this specific behavior documented anywhere.

I think it would make sense for set_pipeline to just unarchive pipelines to an unpaused state, since it's no different from creating a pipeline that has some history. I would also be okay with adding a flag on the step to enable this behavior.

[saj]

Yes, please! I was very surprised to learn that set_pipeline is not deterministic.

In our case, we set_pipeline on the appearance of a new VCS branch. With current Concourse behaviour:

1. A new branch head with name foo appears. set_pipeline creates a new (unpaused) pipeline and all is hunky dory.
2. Branch foo is unpushed. The pipeline is archived. OK.
3. A new branch head with name foo appears. set_pipeline does nothing.