Setting `cache-control` for a wildcard slug at the root overrides cache headers for static assets

### Link to the code that reproduces this issue https://github.com/jasons42/next-static-cache-override-bug ### To Reproduce 1. Start the application in development 2. Load the homepage 3. Inspect cache-control header on versioned static assets in the browser tools ### Current vs. Expected behavior # Current behaviour Next sets `cache-control: public, max-age=10` for immutable assets in the `/_next/static` directory. <img width="1251" alt="Image" src="https://github.com/user-attachments/assets/27fc158f-124d-4a57-a043-8ce5af7de24c" /> # Expected behaviour Next should not allow overriding of `cache-control` headers for the `/_next/static` directory, as per the [documentation](https://nextjs.org/docs/app/api-reference/config/next-config-js/headers#cache-control) > Next.js sets the Cache-Control header of public, max-age=31536000, immutable for truly immutable assets. It cannot be overridden. These immutable files contain a SHA-hash in the file name, so they can be safely cached indefinitely. For example, [Static Image Imports](https://nextjs.org/docs/app/getting-started/images#local-images). You cannot set Cache-Control headers in next.config.js for these assets.<br><br>However, you can set Cache-Control headers for other responses or data. ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:43 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T8132 Available memory (MB): 32768 Available CPU cores: 10 Binaries: Node: 22.9.0 npm: 10.8.3 Yarn: 1.22.22 pnpm: N/A Relevant Packages: next: 15.4.0-canary.93 // Latest available version is detected (15.4.0-canary.93). eslint-config-next: N/A react: 19.1.0 react-dom: 19.1.0 typescript: 5.8.3 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Headers, Dynamic Routes ### Which stage(s) are affected? (Select all that apply) next dev (local), next start (local), Other (Deployed…