SSR Locale Broken? Check Your Wrangler Entry Point

The problem

SSR HTML always renders in the base locale. /fr pages come back in English. The client hydrates and flashes to French a moment later.

paraglideMiddleware in src/server.ts should set the locale before rendering. It never runs.

The cause

@cloudflare/vite-plugin reads the main field from wrangler.jsonc to resolve the server entry. The standard Cloudflare + TanStack Start docs say to set:

{ "main": "@tanstack/react-start/server-entry" }

That's TanStack Start's default handler. It doesn't know about your src/server.ts. Your middleware is dead code.

The fix

{ "main": "./src/server.ts" }

Now the Cloudflare plugin loads your file, paraglideMiddleware runs, getLocale() returns the right locale during SSR.

server.ts

import { paraglideMiddleware } from "./paraglide/server.js"
import handler from "@tanstack/react-start/server-entry"

export default {
  fetch(req: Request): Response | Promise<Response> {
    return paraglideMiddleware(req, () => handler.fetch(req))
  },
}

Pass the original req to handler.fetch — not the middleware's delocalized request. TanStack Router handles URL rewriting via deLocalizeUrl/localizeUrl in its rewrite config. Passing the delocalized request causes redirect loops.

Why it's easy to miss

TanStack Start auto-discovers src/server.ts via its own Vite plugin. But the Cloudflare Vite plugin has its own entry resolution that takes precedence. The issue only appears when both plugins are in play.