Vite proxied `flutter run -d chrome` does not respond with RunRequest

I'm proxying flutter run -d chrome --web-port 5710 through a Vite proxy and it doesn't respond with a RunRequest over the dwds websocket. When flutter.js, proxied through vite to run embedded in a Svelte app, creates the connection to the WebSocket, RunRequest never gets returned from the WebScoket.

Here is the code I can manually run in the console to get a RunRequest (I copied this by going to http:localhost:5710 and copying ConnectRequest from the Network tab):

const ws = new WebSocket('ws://localhost:5173/$dwdsSseHandler')
ws.send('["ConnectRequest","appId","Im4Su93feIfeEOgiTPFjmA==","instanceId","006dcb10-0d68-11ef-907d-716f5f111410","entrypointPath","main_module.bootstrap.js"]')

RunRequest is returned in response to the ConnectRequest through the WS proxy, so I've verified it's not the WebSocket proxy or a hostname origin issue. Do you have any ideas why this wouldn't respond with this event?

Here is the vite config:

import {sveltekit} from '@sveltejs/kit/vite'
import {defineConfig} from 'vite'

export default defineConfig({
    server: {
        proxy: {
            '/dev/ui': {
                rewrite: (path) => path.replace(/^\/dev\/ui\//, '/'),
                target: 'http://localhost:5710',
                ws: true,
            },
            '/$dwdsSseHandler': {
                target: 'http://localhost:5710',
                ws: true,
            },
        },
    },
    plugins: [sveltekit()],
})

dart-lang / webdev

Vite proxied `flutter run -d chrome` does not respond with RunRequest #2425