If you are trying to share context between middleware (backend) and rendering (frontend) literally rather than logically (via request-id only) then that seems to stem from a fundamental misconception of the distinction between backend and frontend to me ...

I suspect all these "all-in-one" JS frameworks out there unfortunately made people think that web apps are made of "one big happy javascript application, yay!" while it's really two (or even three) entirely decoupled runtimes (backend & frontend) instead.