Production builds are not reproducible: every reflex export renames every script #7562

Describe the bug

Two reflex export --frontend-only runs of the same source produce different files: every script under assets/ gets a new name, and React Router's manifest gets a new version. So every deploy looks like a new frontend to a browser, even when only Python changed.

There are two causes:

1. state.js imports all of .web/reflex.json (import reflexEnvironment from "$/reflex.json"), but only reads reflexEnvironment.version (the socket subprotocol). The file also holds project_hash, a random uuid written by init_reflex_json when the web folder is created, and last_reflex_run_datetime, rewritten by set_last_reflex_run_time() on every run. Both end up in the state.js chunk, so its name changes, and with it the name of every chunk that imports it.
2. An f-string id around a Var gets a ref name that changes between runs. Var.__format__ writes <reflex.Var>{hash(var)}</reflex.Var>{js_expr} into the string, and format_ref keeps the hash digits in the ref name. The hash can include memory addresses (id()), so rx.box(id=f"zone-{item}") compiles to a different ref_..._<digits>_... name in each run.

To reproduce

for i in 1 2; do
  REFLEX_WEB_WORKDIR=/tmp/build$i reflex export --frontend-only --no-zip --env prod
done
ls /tmp/build1/build/client/assets | grep manifest
ls /tmp/build2/build/client/assets | grep manifest
diff -rq /tmp/build1/build/client /tmp/build2/build/client

Expected behavior

The same source gives the same files. Content-hashed file names only change when the content changes, which is their purpose.

Why it matters

• Browsers re-download every script after every deploy, even when no page changed.
• During a Kubernetes rolling update, pages and scripts come from pods with different builds even when the source is the same. A page from a new pod asks an old pod for scripts it does not have; the 404 makes React Router reload the page at once (loadRouteModule), on every deploy, including Python-only ones.
• An app cannot tell "the frontend changed" from "the backend was redeployed" by comparing build names.

Environment

Reflex 0.10.0, and main at d02ba54. Node 24, Vite build via reflex export.