Thanks for @greg-449 for the directions.

It turns out the injection system is not even initialized until PlatformUI.createAndRunWorkbench is ran.

I have found however that my TreeModelView class is created with working DI. Which is apparently because it is mentioned in plugins.xml It is still not clear whether I have (or need) a central point where I can register my own beans, but I could do so here with the ones needed there.

First of all, to inject the OSGI service inez I did not have to do anything beyond using @Inject in that class. I have even deleted basically all of the start() function of my bundle activator which was previously obtained the service.

I could also @Inject IEclipseContext, and use that tho create my own bean. I did that with my ModelTreeContentProvider class, which in turn again uses inez using injection:

public class TreeModelView extends ViewPart {
    public static final String ID = "io.github.magwas.inez.ui.treeModelView";

    @Inject
    IWorkbench workbench;

    @Inject
    Inez inez;

    @Inject
    IEclipseContext eclipseContext;

    private TreeViewer viewer;

    @Override
    public void createPartControl(Composite parent) {
        Assert.notNull(inez, "inez is null");
        ModelTreeContentProvider provider = ContextInjectionFactory
                .make(ModelTreeContentProvider.class, eclipseContext);
                //normal eclipse viewer stuff from here, deleted for brewity
        
    }

    @Override
    public void setFocus() {
        viewer.getControl().setFocus();
    }

}

public class ModelTreeContentProvider implements ITreeContentProvider {

    @Inject
    Inez inez;

    @Override
    public Object[] getElements(Object inputElement) {
        System.out.println("getElements " + inputElement);
        return inez.root().getChildren().toArray();
    }
//[...]
}

I also tried to just add a @Singleton annotation to my ModelTreeContentProvider class and inject it to my TreeModelView, but that did not work. Apaprently I have to register my beans using ContextInjectionFactory by hand. So until I find some central space where I can make all my beans early, I just use some of my views and editors for that, and factor out their business logic to some services.