@hono/node-server/vercel: POST requests hang (no response) on Vercel Node runtime while GET works

[leohahn]

What version of Hono?

• hono@4.11.9
• @hono/node-server@1.19.9

What version of Node.js?

• Vercel function runtime nodejs24.x

What happened?

Using the official Vercel adapter from @hono/node-server/vercel:

import { handle } from '@hono/node-server/vercel'
import app from '../apps/api/src/server.js'

export default handle(app)

in a Vercel function (api/server.ts) with rewrites (/api/* and /rpc/* -> /api/server), GET requests work, but POST requests never return a response (client times out).

Repro matrix from Preview deployment:

Case	Method	Path	Result
health	GET	/api/health (separate function)	200
slack-url-verification	POST	/api/slack	timeout (curl exit 28 after 25s)
slack-interactivity-invalid-signature	POST	/api/slack/interactivity	timeout (curl exit 28 after 25s)
rpc-ping-no-csrf	POST	/rpc/ping	timeout (curl exit 28 after 25s)
rpc-ping-csrf-no-auth	POST	/rpc/ping	timeout (curl exit 28 after 25s)

When we switch back to a custom Node IncomingMessage/ServerResponse bridge that buffers the request body and calls app.fetch(request), the same POST routes return immediately with expected app-level responses.

Minimal reproduction steps

1. Deploy a Vite + Hono app on Vercel with:
   • API function at api/server.ts
   • rewrites /api/:path((?!health$|server$).*) -> /api/server and /rpc/(.*) -> /api/server
2. Use @hono/node-server/vercel handle(app) as above
3. Call POST route (JSON or form-encoded) via Preview URL
4. Observe no response body/status until client timeout

Expected

POST routes should behave like GET routes and return app responses.

Actual

POST routes hang indefinitely on Vercel Node runtime.

Additional context

• Using hono/vercel in this same Node function setup also hangs, but that appears to be a signature mismatch (Request handler in Node req/res runtime).
• The issue here is specifically with the Node-targeted Vercel adapter from @hono/node-server/vercel.