`next build` shows generic "Invalid segment configuration export detected" when `config.matcher` uses `String.raw` in `proxy.ts`

Link to the code that reproduces this issue

https://github.com/ahxar/next-proxy-string-raw-repro

To Reproduce

1. Clone the reproduction repo.
2. Install dependencies:

   npm install
   

3. Run:

   npm run build
   

4. Observe this error at the end of build:

   ⨯ Invalid segment configuration export detected. This can cause unexpected behavior from the configs not being applied. You should see the relevant failures in the logs above. Please fix them to continue.
   

5. In src/proxy.ts, remove String.raw and use a plain string literal in config.matcher.
6. Run npm run build again and it succeeds.

Current vs. Expected behavior

Current behavior:

• Build fails with a generic segment config error.
• Message says "You should see the relevant failures in the logs above", but there is no actionable failure pointing to src/proxy.ts / config.matcher.

Expected behavior:

• Error should clearly identify src/proxy.ts and explain that config.matcher must be statically analyzable (or literal), with a specific diagnostic for String.raw.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.2.0
Binaries:
  Node: 24.11.1
  npm: 11.6.2
  Yarn: N/A
  pnpm: 10.28.1
Relevant Packages:
  next: 16.1.3
  react: 19.2.3
  react-dom: 19.2.3
  typescript: 5.9.3
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

• Reproducible locally.
• The issue is specifically about error reporting quality: the build failure reason is not pinpointed even though the root cause is String.raw in config.matcher inside proxy.ts.

Start with the reproduction repository's src/proxy.ts and run npm install followed by npm run build to observe the generic diagnostic. Trace the next build handling of config.matcher when it contains String.raw, then make the failure identify src/proxy.ts and explain the static-analysis requirement; done means the diagnostic is actionable and the plain-string case still builds successfully.