edit: to answer my own question: No https://www.reddit.com/r/Stadia/comments/hrsypo/does_read_de...
But it's still a rhetorical question: like, I'm surprised the infrastructure between Stadia and regular PC was so different that Stadia was effectively its own console. I assumed it was just a somewhat thicker version of something like Nvidia's GeForce, which let you (for the most part) access your own Steam library.