HMR WebSocket fails - middlewareMode prevents Vite's WebSocket handler

Summary

HMR WebSocket connections fail when using marko-run dev. The WebSocket upgrade request returns 404 instead of 101 Switching Protocols.

Environment

• @marko/run: 0.9.3
• vite: 7.2.2
• Node.js: 20.x

Reproduce Steps

1. Run marko-run dev
2. Access the dev server through any proxy (Cloudflare Tunnel, nginx, etc.)
3. Open browser DevTools → Network → WS filter
4. Observe WebSocket returns 404, HMR doesn't work

Root Cause

In src/adapter/dev-server.ts:

server: { ...config?.server, middlewareMode: true }

Then in startDev:

const listener = devServer.middlewares.listen(port, ...);

The problem:

• middlewareMode: true tells Vite NOT to create its own HTTP server (devServer.httpServer is null)
• middlewares.listen() creates a NEW HTTP server
• This new server doesn't have Vite's WebSocket upgrade handler attached
• WebSocket upgrades get routed as HTTP GET → 404

Proof

• Raw npx vite → WebSocket returns 101 Switching Protocols ✅
• marko-run dev → WebSocket returns 404 ❌

Proposed Fix

// Don't use middlewareMode
server: { ...config?.server, middlewareMode: false }

// Use Vite's httpServer
devServer.httpServer.listen(port, ...);

Workaround

Users can use patch-package to patch node_modules/@marko/run/dist/adapter/index.js:

1. Change middlewareMode: true to false
2. Change devServer.middlewares.listen() to devServer.httpServer.listen()

Start in src/adapter/dev-server.ts, focusing on the server configuration and startDev entry point described in the issue. Reproduce the failure with marko-run dev through a proxy and compare its WebSocket setup with raw Vite. Done means the proxied HMR connection receives 101 Switching Protocols instead of 404.