Tanstack Start: Cannot route to agents

[imaai]

There is this wierd bug occuring when you try to route the request to agents in tanstack start.

A header value for "X-Miniflare-Durable-Object-Cf-Blob" contains non-ASCII characters 
[...]. 
As a quirk to support Unicode, we are encoding values as UTF-8 in the header, but in a browser this would likely result in a TypeError exception. 
Consider encoding this string in ASCII for compatibility with browser implementations of the Fetch specification.

Context

// src/server.ts
import handler from "@tanstack/react-start/server-entry";
import { routeAgentRequest } from "agents";
  
export default {
    fetch: async (request: Request, env: Env, ctx: ExecutionContext) => {
        const response = await routeAgentRequest(request, env)
        if (!response) {
            return handler.fetch(request)
        }
        return response
    },
}

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "name": "tanstack",
  "compatibility_date": "2025-09-02",
  "compatibility_flags": [
    "nodejs_compat"
  ],
  "main": "./src/server.ts",
  "durable_objects": {
    "bindings": [
      {
        "name": "Counter",
        "class_name": "Counter",
        "script_name": "src/agents/counter.ts"
      }
    ]
  }
}

const config = defineConfig({
  plugins: [
    cloudflare({ viteEnvironment: { name: 'ssr' } }),
    devtools(),
    // this is the plugin that enables path aliases
    viteTsConfigPaths({
      projects: ['./tsconfig.json'],
    }),
    tailwindcss(),
    tanstackStart(),
    viteReact(),
  ],
})