I researched Artifact Mastery, the description for which is shown in the first screen snapshot below.  Given the description, I would expect to be able to build an improvement on an available hex called "Precursor Nanites".  However, after completing the research there is no new improvement available for me to build.  The second screen snapshot below shows the screen for one of my worlds and there is no improvement called "Precursor Nanites" available for me to build.

Is this a bug or do I just not understand what benefit researching Artifact Mastery is supposed to provide?