`response.body?.cancel()` of `fetch` causes unexpected behaviors in App Router

### Link to the code that reproduces this issue https://codesandbox.io/p/devbox/lucid-cohen-8r5tyq?workspaceId=cf95a29a-9e60-48fa-8cf5-0d217db0d3c6 ### To Reproduce 1. Build and start server (`npm run build && npm run start`) 2. Access `/` ### Current vs. Expected behavior ### Expected: - The `ReadableStream` (`response.body`) is successfully cancelled. ### Current: - `response.body?.cancel()` does not resolve, causing the page to not return. - Once `response.body?.cancel()` is called, the Next.js server does not terminate when `Ctrl + C` is pressed in the terminal. ### Provide environment information ```bash Operating System: Platform: linux Arch: x64 Version: #1 SMP Fri Mar 29 23:14:13 UTC 2024 Available memory (MB): 39993 Available CPU cores: 20 Binaries: Node: 22.11.0 npm: 10.9.0 Yarn: 1.22.15 pnpm: 9.10.0 Relevant Packages: next: 15.0.2 // Latest available version is detected (15.0.2). eslint-config-next: 15.0.2 react: 19.0.0-rc-02c0e824-20241028 react-dom: 19.0.0-rc-02c0e824-20241028 typescript: 5.6.3 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Not sure ### Which stage(s) are affected? (Select all that apply) next start (local), Other (Deployed) ### Additional context Reproduced with not only Next.js v15.0.2 but also v14.2.17 at least. I know the way to get only header or consume body in other way. This issue focuses on the bug with `response.body.cancel`.