Very nice writeup! However, the example did not fully work for me. I could perform CRUD on a single tab, but opening the list in multiple tabs did not replicate the list or actions. Seeing this in the console:

  [Error] Could not connect to the server.
  [Error] Fetch API cannot load https://damp-fire-554.fly.dev/replicache-pull?list_id=kx1I-gXPWwOxU9teRUJ_c due to access control checks.
  [Error] Failed to load resource: Could not connect to the server. (replicache-pull, line 0)

Safari 14.2 on macOS 10.15.7.