In the end the issue happens because our librcc0 sub-library has no requirements to its engine libs (rcc-runtime). Instead the runtime requirement was added to the main librcc which doesn't exist at all.
Of course there'll be regressions if we don't follow what upstream suggests(use special lib for special purpose). But since librcc supports dynamic engines, in this case I can update without introducing a new package.
And meanwhile I updated our libguess/librcc with the new mechanism for Factory and further versions.