Tree shaking in middleware doesn't work

Link to the code that reproduces this issue

https://github.com/amannn/nextjs-bug-repro-middleware/commit/6c442b025f45b0f777fda6f32fc355e58bef1fb9

To Reproduce

1. Run pnpm i && pnpm build
2. See console output and analyzer output

Current vs. Expected behavior

Console output:

ƒ Middleware                             1.07 MB

I'd expect getMessages to not be bundled into the middleware as it's not used there.

See also the analyzer output:

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: 15.1.5 // Latest available version is detected (15.1.5).
  eslint-config-next: N/A
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.3
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)

next build (local)

Additional context

No response

Start with the linked reproduction at commit 6c442b025f45b0f777fda6f32fc355e58bef1fb9 and run pnpm i && pnpm build. Inspect the middleware bundle and analyzer output to trace why getMessages is included; done means the middleware no longer bundles that unused function.