--experimental-build-mode=compile does not set cache headers

### Link to the code that reproduces this issue https://codesandbox.io/p/devbox/youthful-currying-9vwzgy ### To Reproduce 1. Create a root layout with: ``` export const dynamic = "force-static"; export const revalidate = 86400; ``` 2. Add some dynamic route segment, e.g. slug, later used with values unknown at build time. 3. Run regular `next build`, start your production build 4. Fetch your dynamic route, observe that Response has the header: `cache-control s-maxage=86400, stale-while-revalidate=31449600` 5. Run `next build --experimental-build-mode=compile`, followed by `next build --experimental-build-mode=generate-env` (The latter would run at container startup, that's the separation of concerns that seems reasonable to me) 6. Observe that response has header: `cache-control private, no-cache, no-store, max-age=0, must-revalidate` 7. Repeat with build mode compile, but this time finish with `next build --experimental-build-mode=generate` 8. Observe that the cache headers are present again. ### Current vs. Expected behavior Since these routes are not rendered at build time, the generate step should not be required in order to be able to pass cache control headers for dynamic routes. I think I understand the implication that `--experimental-build-mode=compile` without being followed by `generate` opts out of SSG/ISR into fully-dynamic and `revalidate` not working anymore to derive cache headers is a sideeffect, but there should be some other pattern for pages to be able to set cache headers then. ### Provide environment information ```bash next 15.5.2 ``` ### Which area(s) are affected? (Select all that apply) Dynamic Routes, Headers ### Which stage(s) are affected? (Select all that apply) next build (local), next start (local), Other (Deployed), Vercel (Deployed) ### Additional context I think this is not specific to dynamic routes and applies to fixed ones aswell, but using a dynamic route helped rule out static generation as a factor why the one build mode wor…