zip to cdi conversion can actually mean two things, with the first being the obvious extraction of ZIP archives that contain .cdi files. Alternative to this is repacking ZIP content for DiscJuggler images (.cdi), that should be possible with some tools.
But overall CDI format is almost three decades old, so this is probably done for a highly specific purpose. We do did not however, find any specifics about this.
Updated: September 12, 2023