If I understand LR CC correctly, it pulls a smart preview from the cloud for me to work with on my laptop (assuming my catalog and collections are originating from a desktop using LR Classic), so if I choose to edit a file in PS CC and decide to save or export from there, how does that process work?
In other words, since I'm not working with the original file in Lightroom CC, is it correct to assume you aren't working with the original file in Photoshop (if opened from LR CC)? If so, how does that translate back into LR or to export?
In case that LR CC only has a smart preview, then it will use this in photoshop. For whatever reason it calls it a dng file while you work with it. When you save, it is saved as Tiff ( in my Photoshop at least) and then uploaded to CC and stacked with your original smart preview. The Tiff is called *-edit.tiff in LR CC as you can see with the info button. That Tiff is then downsynced into your shared CCCL collection and appears there next to your original file where the smart preview was uploaded in CC, of course with the limited resolution pertinent to smart previews. When you delete that Tiff in CC, then it is removed from CCCL.
(when you edit a smart preview in CC, then changes are downsynced to CCCL and these are applied to your original there, hence you retain changes in full resolution)