Christopher Francisco, Elia Zammuto, and Jens Villadsen,
Andrew Bayer has released a fix for the issue, and I'm pretty sure that once you update the plugin versions, this problem will be resolved. Since at least one of you is new to setting up your own Jenkins, here's how to go about it:
1. Launch your container and log in if necessary:
2. In the navigation bar at the left, click "Manage Jenkins." That'll take you to the below screen, where you'll want to pick "Manage Plugins." In the below screenshot, "Manage Plugins" is highlighted, but I haven't clicked it yet:
3. Once there, you should see the Manage Plugins screen, with the "Updates" tab preselected for you. If your list looks empty or nearly empty, click the "Check Now" button. That should produce a list much like what you see here:
4. Click "Select All," then click "Download now and install after restart."
5. You'll see the updates taking place. Click the checkbox at the bottom to restart Jenkins once it's ready.
6. Once it's back up, if you go back to Manage Plugins and check the "Installed" tab, you should see that your versions of the `pipeline-model-definition` and its related plugins have been updated to 1.2.9. You can spot this easily by looking for the "Downgrade to 1.2.8" buttons at the right.
7. For historical purposes, here's my install before taking the updated version of pipeline-model-definition. As you can see, the Pipeline editor does not show the Agent settings, which is exactly the bug reported here:
8. And now, with the upgrades in place, the Agent dropdown is available in the Pipeline Editor:
I hope that's helpful if we have newcomers to Jenkins looking at this issue.
Thanks again for reporting the bug! I'm going to go ahead and mark it as Resolved, but feel free to follow up here if you run into any trouble.