Following JBIDE-17690 :

mistria@redhat.com said :

You say that since it's already embedded, it should not appear on software page. Then I have the regret to tell you that this is a bad assumption. Things are shown on Central page unless the CONNECTOR is already installed, not its contained IUs. So even if Forge is already included, it is shown anyway. I you need another behaviour, this requires some work on Central.
I now remember that I had to update the TP on Monday morning before releasing CR1a to add Forge on Discovery. Installation-tests were failing without it: https://github.com/jbosstools/jbosstools-discovery/commit/41885e7e9b2e7ca20ed3dc999820bdcf51e2d9b0 , showing that it was impossible to install Forge in JBDS.
So this means that not all features from Forge are available in JBDS, and that at least one of them (I don't remember which one-s) need to be added to Discovery site for effective installations.