N.B. This is exactly how seaside, vba, and even arc[1] do server-side state generally: by encrypting the blob-representing-state and sending to the client to be sent back on future requests (where it will be decrypted and rehydrated).

It's an old trick that everyone designing protocols should know, since there are lots of applications beyond AI companies.

[1]: As in, pg's lisp: https://arclanguage.github.io/ref/srv.html#:~:text=The%20pre...