TurbopackInternalError when outputFileTracingRoot path is invalid

[Daves1245]

Link to the code that reproduces this issue

https://github.com/Daves1245/nextjs-config-issue-example

To Reproduce

npm i
npm run build

Current vs. Expected behavior

Expected: A clear error should mention the outputFileTracingRoot configuration issue.
Actual: Turbopack panics with an internal error.

FATAL: An unexpected Turbopack error occurred. A panic log has been written to /tmp/next-panic-da8431fdb961198c2c41186f79b7b442.log.

To help make Turbopack better, report this error by clicking here: https://github.com/vercel/next.js/discussions/new?category=turbopack-error-report&title=Turbopack%20Error%3A%20Invalid%20distDirRoot%3A%20%22.next%22.%20distDirRoot%20should%20not%20navigate%20out%20of%20the%20projectPath.&body=Turbopack%20version%3A%20%60d1bd5b58%60%0ANext.js%20version%3A%20%600.0.0%60%0A%0AError%20message%3A%0A%60%60%60%0ATurbopack%20Error%3A%20Invalid%20distDirRoot%3A%20%22.next%22.%20distDirRoot%20should%20not%20navigate%20out%20of%20the%20projectPath.%0A%60%60%60&labels=Turbopack,Turbopack%20Panic%20Backtrace
-----

Error [TurbopackInternalError]: Invalid distDirRoot: ".next". distDirRoot should not navigate out of the projectPath.

Debug info:
- Execution of Project::project_fs failed
- Invalid distDirRoot: ".next". distDirRoot should not navigate out of the projectPath.
    at <unknown> (TurbopackInternalError: Invalid distDirRoot: ".next". distDirRoot should not navigate out of the projectPath.) {
  location: undefined
}

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #91-Ubuntu SMP PREEMPT_DYNAMIC Tue Nov 18 14:14:30 UTC 2025
  Available memory (MB): 64031
  Available CPU cores: 20
Binaries:
  Node: 22.13.0
  npm: 11.4.1
  Yarn: 1.22.22
  pnpm: 9.6.0
Relevant Packages:
  next: 16.1.1 // Latest available version is detected (16.1.1).
  eslint-config-next: 15.1.6
  react: 19.1.1
  react-dom: 19.1.1
  typescript: 5.8.3
Next.js Config:
  output: N/A

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

Turbopack, Error Handling

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

next build (local)

Additional context

No response

[mrose]

In my case this was caused by an invalid path in next.config.ts
e.g.:
turbopack: {
root: -- invalid value was here --
}

[Daves1245]

outputFileTracingRoot is given preferential treatment, but in its absence specifying an invalid root also crashes turbopack. #87883 should cover both options