It seems as if doc/kcontrol/cddbretrieval was removed.
Created attachment 314761 [details] build.log
This is one of the issues still open for the 4.8.4 bump. I hit it but wasn't able to solve it before pushing the ebuilds to the overlay.
It looks to me it went from kdemultimedia-4.8.3/doc/kcontrol/cddbretrieval to kdemultimedia-4.8.4/libkcddb/kcmcddb/doc So i think it should be installed by libkcddb and not by kscd?
The handbook has been removed from kscd (all versions) and moved to libkcddb (4.8.4). I am unsure of how to proceed with the remaining versions of libkcddb, since they cannot use the KMEXTRA/KMEXTRACTONLY trick due to upstream moving to split repos/tarballs.
4.8.4 is now in the tree, and the handbook is now being installed by kdemultimedia-kioslaves.