Router duplicates base path when using pages with shared parent in both page and app router

### Link to the code that reproduces this issue https://github.com/gabrielricardourbina/nextjs-route-bug ### To Reproduce Have pages with a shared parent in both Page and App router **and** having a basePath For example ``` . ├── pages │ └── parent │ └── [parentId] │ └── child │ ├── [childId] │ │ └── grand-child │ │ └── [grandChildId].tsx │ └── [childId].tsx └── src └── app └── parent └── [parentId] └── page.tsx ``` Where `parent` is shared in both routers ### Current vs. Expected behavior ## Case A from App Router to Page Router ✅ Navigating from `parent/[parentId]` to `parent/[parentId]/child/[child]` or `parent/[parentId]/child/[child]/grand-child/[grandChildId]`, results in the respective pages being rendered and the url matching the folder structure with the basePath being prepended correctly ## Case B from Page Router to App Router ✅ Navigating from `parent/[parentId]/child/[child]` or `parent/[parentId]/child/[child]/grand-child/[grandChildId]` to `parent/[parentId]`, results the page being rendered and the url matching the folder structure with the basePath being prepended correctly ## Case C from Page Router to Page Router ❌ Navigating from `parent/[parentId]/child/[child]` to `parent/[parentId]/child/[child]/grand-child/[grandChildId]` or from `parent/[parentId]/child/[child]/grand-child/[grandChildId]` to `parent/[parentId]/child/[child]`, results in a redirection to a non-existing page where the basePath is duplicated I.E. `/base/base/*` ## Video https://github.com/user-attachments/assets/3b990434-6166-4e5d-8c2f-8d0e284bf9c4 ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.2.0: Fri Dec 6 18:51:28 PST 2024; root:xnu-11215.61.5~2/RELEASE_ARM64_T8112 Available memory (MB): 24576 Available CPU cores: 8 Binaries: Node: 18.20.2 npm: 9.9.4 Yarn…