Encoding issue with middleware rewrites and search params

[amannn]

Link to the code that reproduces this issue

amannn/nextjs-bug-repro-middleware-encoding@cdf1f30

To Reproduce

1. Deploy https://github.com/amannn/nextjs-bug-repro-middleware-encoding/ on Vercel
2. Open the app with ?sélectionnez+votre in the pathname

Example deployment: https://nextjs-bug-repro-middleware-encoding.vercel.app/?s%C3%A9lectionnez+votre

Current vs. Expected behavior

Errors from Vercel:

500: INTERNAL_SERVER_ERROR
Code: MIDDLEWARE_INVOCATION_FAILED
ID: fra1::fvjhx-1747217023943-0c711de933e3

Vercel Runtime Malformed Response Header Error: Header 'x-middleware-rewrite: /test?s%C3%A9lectionner+votre' contains non-ASCII characters.

I'd expect the app to work.

Provide environment information

Operating System:
  Platform: darwin
  Arch: x64
  Version: Darwin Kernel Version 23.6.0: Mon Jul 29 21:13:00 PDT 2024; root:xnu-10063.141.2~1/RELEASE_X86_64
  Available memory (MB): 16384
  Available CPU cores: 12
Binaries:
  Node: 20.11.1
  npm: 10.2.4
  Yarn: 1.22.22
  pnpm: 9.15.4
Relevant Packages:
  next: 15.4.0-canary.34 // Latest available version is detected (15.4.0-canary.34).
  eslint-config-next: 15.4.0-canary.34
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

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

Middleware

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

Vercel (Deployed)

Additional context

No response