Unhandled rejection when using rewrite proxy

[JeremieDoctrine]

Link to the code that reproduces this issue

https://github.com/JeremieDoctrine/next-proxy-issue

To Reproduce

pnpm install
pnpm run dev
curl http://localhost:3000/proxy-path

You can see in the logs

⨯ unhandledRejection: [Error: getaddrinfo ENOTFOUND not-existing-host] {
  errno: -3008,
  code: 'ENOTFOUND',
  syscall: 'getaddrinfo',
  hostname: 'not-existing-host'
}

Current vs. Expected behavior

Currently the proxy is throwing an unhandledRejection.

The expected behavior is not to throw an unhandledRejection.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.0.0: Tue Sep 24 23:38:45 PDT 2024; root:xnu-11215.1.12~1/RELEASE_ARM64_T8122
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 21.7.3
  npm: 10.5.0
  Yarn: 1.22.22
  pnpm: 9.12.3
Relevant Packages:
  next: 15.0.4-canary.2 // Latest available version is detected (15.0.4-canary.2).
  eslint-config-next: N/A
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.6.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Not sure

Which stage(s) are affected? (Select all that apply)

next dev (local), next start (local), Other (Deployed)

Additional context

The issue was introduced in this PR : #65759 from @wyattjoh

Commenting this line :

next.js/packages/next/src/server/lib/router-utils/proxy-request.ts

Line 89 in 55552ba

detached.reject(err)

fixes the issue but i'm not sure what is the expected behavior.

[JeremieDoctrine]

I tried a fix here : #72530