I still sense there is something specifically peculiar to Bulgakov going on here (that I still don’t fully understand) that is very important to him (in his sense of what Spirit is and does). It feels new to me, like I haven’t encountered it before. (While panentheism is familiar in many respects.)

By the way, your section about how “The Holy Spirit is the ‘ontic foundation of the world’ in a way ‘that corresponds to the action of the Third Hypostasis in the Divine Sophia’ (200)” — given Bulgakov’s mariology — reminds me of the “spirit of God” brooding over the face of the deep (in Genesis 1) like a mother bird over a nest…incubating life and bringing in forth into its fullness of being.