Repository: next.js
Issue: Error: Failed to load script when using basePath and navigating from pages to app router
Labels: bug,Navigation,Turbopack,Pages Router,linear: turbopack,Module Resolution

### Link to the code that reproduces this issue

https://github.com/seanparmelee/nextjs-pages-to-app-router

### To Reproduce

1. Run `npm run dev` (or `npm run dev:turbo` for turbo mode)
2. Navigate to http://localhost:3000/foo
3. Click the link
4. Observe the errors in the browser console (also in the server console when using turbo mode)

### Current vs. Expected behavior

I expected the page to load without any errors, but instead the page loads and the browser contains a couple errors:
```
GET http://localhost:3000/foo/_next/static/chunks/pages/bar.js net::ERR_ABORTED 404 (Not Found)
Error: Failed to load script: /foo/_next/static/chunks/pages/bar.js
```

When running in turbo mode, the following error is emitting on the server side:
```
PageNotFoundError: Cannot find module for page: /bar
    at findPagePathData (/Users/sean.parmelee/Projects/nextjs-pages-to-app-router/node_modules/next/dist/server/dev/on-demand-entry-handler.js:328:15)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async Object.ensurePage (/Users/sean.parmelee/Projects/nextjs-pages-to-app-router/node_modules/next/dist/server/dev/hot-reloader-turbopack.js:600:42)
    at async Object.run (/Users/sean.parmelee/Projects/nextjs-pages-to-app-router/node_modules/next/dist/server/dev/hot-reloader-turbopack.js:409:21)
    at async handleRequest (/Users/sean.parmelee/Projects/nextjs-pages-to-app-router/node_modules/next/dist/server/lib/router-server.js:205:43)
    at async requestHandlerImpl (/Users/sean.parmelee/Projects/nextjs-pages-to-app-router/node_modules/next/dist/server/lib/router-server.js:377:13)
    at async Server.requestListener (/Users/sean.parmelee/Projects/nextjs-pages-to-app-router/node_modules/next/dist/server/lib/start-server.js:142:13)
```

### Provide environment information

```bash
Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.4.0: Fri Mar 15 00:10:42 PDT 2024; root:xnu-10063.101.17~1/RELEASE_ARM64_T6000
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 20.12.2
  npm: 10.5.0
  Yarn: 1.22.19
  pnpm: 8.15.2
Relevant Packages:
  next: 14.3.0-canary.34 // Latest available version is detected (14.3.0-canary.34).
  eslint-config-next: N/A
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.1.3
Next.js Config:
  output: N/A
```


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

Module Resolution, Navigation, Pages Router, Turbopack

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

next dev (local)

### Additional context

If you remove the `basePath` from `next.config.js`, then the error no longer happens when navigating.
I downgraded all the way back to Next.js 13.4 since that's when the app router went stable and was still able to reproduce this error. One thing I found interesting with `13.4.0` is that the error happens even if there isn't a `basePath` set. This seems to have been fixed in `13.4.1-canary.2` because starting with that version I no longer see the error unless I set a `basePath`.