basePath is not included in request's URL of route handlers

### Link to the code that reproduces this issue https://github.com/ThangHuuVu/reproduction-app-base-path-route-handler https://reproduction-app-base-path-route-handler.vercel.app/custom ### To Reproduce 1. Pull the reproduction. Install deps: `pnpm i` 2. Start the dev server with `pnpm dev` 3. Go to "http://localhost:3000/custom/hello" ### Current vs. Expected behavior Current: The `req.url` is returned as "http://localhost:3000/hello" Expected: It should return "http://localhost:3000/custom/hello" <img width="1017" alt="Screenshot 2024-03-02 at 13 27 01" src="https://github.com/vercel/next.js/assets/31528554/9f48f635-dc4f-4ce0-90df-1002350549c9"> ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 23.3.0: Wed Dec 20 21:31:00 PST 2023; root:xnu-10002.81.5~7/RELEASE_ARM64_T6020 Available memory (MB): 16384 Available CPU cores: 10 Binaries: Node: 20.8.0 npm: 10.1.0 Yarn: 1.22.21 pnpm: 8.6.10 Relevant Packages: next: 14.1.1-canary.71 eslint-config-next: N/A react: 18.2.0 react-dom: 18.2.0 typescript: 5.1.3 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) App Router, Middleware / Edge (API routes, runtime) ### Which stage(s) are affected? (Select all that apply) next dev (local), Vercel (Deployed), Other (Deployed) ### Additional context Seems that this is the behavior of pages router too. When I add a `pages/api/hello2` API route, it also returns the URL without the `basePath`.