[BUG] Duplicated Location Headers is joined.

[yoohahn]

Describe the bug

This is an issue with it's origin within NextJS, but that might be fixable in OpenNext? It is only an issue running NextJS in a self-hosting environment OR deploying using OpenNext (Cloudflare in my case) and not an issue when deploying to Vercel.

Important note is that this has only been seen on a route that is a catch all slug with the force-static flag set.

Steps to reproduce

1. https://github.com/yoohahn/next-redirect-issue
2. yarn install
3. yarn preview
4. Have the Network Tab Open and then visit http://localhost:3000/en/foo/redirect

In open next we get a chain of 307 -> 200.

1. First will be a 307 with cache headers on it.Open Next:

Since NextJS sends 2 Location headers this two will get joined into a comma list. But there is no way for us to act on this since it is far into the redirect chain.

Vercel:

No cache and only 1 Location header NOT comma separated.

2. And then sent to the url with comma list

Next time I visit the same url it acts as I expect. So it is only an issue the first visit.

Expected behaviour

1. Only 1 Location and not being a comma list of Locations.
2. No cache on the 307

@opennextjs/cloudflare version

1.6.5

Wrangler version

4.28.1

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.6.0: Mon Jul 14 11:30:51 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T8112
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 24.1.0
  npm: 11.3.0
  Yarn: 4.9.4
  pnpm: N/A
Relevant Packages:
  next: 15.5.1-canary.9
  eslint-config-next: N/A
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.9.2
Next.js Config:
  output: N/A

Additional info

I have deployed this worker to Cloudflare with the exact same behaviour as in

Issue on NextJS

vercel/next.js#83057