Ok:
Yes, there is some mechanism which transforms / edits the plugin OSGi bundle. I was not aware of that. Is that documented somewhere?
Basically, if you install the app, the app will be transformed and put into {confluence}/home/plugins-osgi-cache/transformed-plugins/{your-plugin-with-some-extra-timestamps}.jar.
If I open that .jar and inspect the manifest, then I have a gazillion extra imports, including the bucket.user.
I’ll switch to the Spring Config things and I see =). Or is there a way to opt out of any OSGi manifest manipulation?
Update: Trying to switch to Spring Java configuration. But I’m getting unexpected exceptions, see here. Unrelated to Confluence 9 itself, but it blocks me from progressing with Confluence 9 itself.