Link to the code that reproduces this issue

https://github.com/juliansommer/workout-track

To Reproduce

Run pnpm build, you can see /exercises/[exercise] and /exercises/p/[page] are being server rendered on demand despite using generateStaticParams. ISSUE ONLY HAPPENS WITH PPR ON, tested on canary 47 with PPR off. During build it says "Generating static pages (983/983)" but then in the actual output says server rendered. Same issue when using --webpack in build, not turbopack specific. I tried putting "export const dynamic = "force-static" on the 2 routes and that just caused build errors.

Compare main branch on repo (canary with PPR on) to stable branch (canary with PPR off)

Current vs. Expected behavior

Should be like this image, with the routes being static

Instead is like this when PPR is enabled, despite it not being enabled on those routes (adding experimental_ppr = false didnt change it either)

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Home
  Available memory (MB): 16088
  Available CPU cores: 16
Binaries:
  Node: 23.11.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.18.0
Relevant Packages:
  next: 15.6.0-canary.47 // Latest available version is detected (15.6.0-canary.47).
  eslint-config-next: 15.5.4
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Partial Prerendering (PPR), Output, Turbopack, Webpack

Which stage(s) are affected? (Select all that apply)

next build (local), Vercel (Deployed)

Additional context

I tested on canary 30, canary 43, now same issue on latest (47)