🐛 BUG: TypeError: This ReadableStream did not return bytes when using a trpc with SSE

[dandoen]

Which Cloudflare product(s) does this pertain to?

Workers for Platforms

What versions are you using?

Node: 22.12.0, Wrangler 3.99.0

What operating system and version are you using?

macOS 14.0

Please provide a link to a minimal reproduction

https://github.com/dandoen/cloudflare-trpc-subscription

Describe the Bug

Following the example implementation of a basic SSE, deployed to the Cloudflare runtime I'm getting "TypeError: This ReadableStream did not return bytes"

This happens both locally and in deployed environment. It's unclear where the error is being thrown from and/or how I should be handling it.

Please provide any relevant error logs

workerd/io/worker.c++:1017: info: console warning; message = A promise rejection was handled asynchronously. This warning occurs when attaching a catch handler to a promise after it rejected. (rejection #18)
workerd/io/worker.c++:2082: info: uncaught exception; source = Uncaught (in promise); stack = TypeError: This ReadableStream did not return bytes.
workerd/io/worker.c++:2082: info: uncaught exception; source = Uncaught (in response); stack = TypeError: This ReadableStream did not return bytes.
workerd/io/worker-entrypoint.c++:372: info: exception = workerd/jsg/_virtual_includes/jsg/workerd/jsg/value.h:1372: failed: remote.jsg.TypeError: This ReadableStream did not return bytes.
stack: 104b5993b 104b50e14 104b51c8f 1068fa0e3 1049faaf0 1049faebc 1049fc0d8 1049fcacc 104a5b6b7 10445bd60 105383337 1068fa0e3 105381f70 10445bd60 104b51044 104b5145b 1068fa0e3 1049fc2c8 1049fcacc
workerd/server/server.c++:3898: error: Uncaught exception: workerd/jsg/_virtual_includes/jsg/workerd/jsg/value.h:1372: failed: remote.jsg.TypeError: This ReadableStream did not return bytes.
stack: 104b5993b 104b50e14 104b51c8f 1068fa0e3 1049faaf0 1049faebc 1049fc0d8 1049fcacc 104a5b6b7 10445bd60 105383337 1068fa0e3 105381f70 10445bd60 104b51044 104b5145b 1068fa0e3 1049fc2c8 1049fcacc 1044b9fa7 1053936a3 1053946bf 1053950f7 105367e80
[InspectorProxyWorker] RUNTIME INCOMING MESSAGE {
  method: 'Runtime.exceptionThrown',
  params: {
    timestamp: 1736235620722,
    exceptionDetails: {
      exceptionId: 17,
      text: 'Uncaught (in promise)',
      lineNumber: 0,
      columnNumber: -2,
      url: 'undefined',
      exception: [Object],
      executionContextId: 321189153
    }
  }
}

[dandoen]

Do note, I'm suspecting this is a bug on the Cloudflare side because running the router as an http server works just fine

import { createHTTPServer } from '@trpc/server/adapters/standalone';

// in https://github.com/dandoen/cloudflare-trpc-subscription/blob/master/src/index.ts#L21
createHTTPServer({
	router,
	createContext() {
		return {};
	},
}).listen(2022);