[Turbopack] Pages Router hydration delayed when tab opened in background

Link to the code that reproduces this issue

https://github.com/happyjosh/turbopack-pages-router-bug

To Reproduce

1. Create minimal _app.tsx with timing logs
2. Use yarn dev --turbopack
3. Middle-click a link to open page in background tab
4. Switch to the new tab and check console logs

Current vs. Expected behavior

When opening a Pages Router page in a background tab (middle-click or right-click -> open in new tab), the hydration is significantly delayed until the tab becomes visible.

Observed behavior:

• Module loads at ~1200ms with visibilityState: hidden
• App render happens at ~9200ms with visibilityState: visible
• ~8 seconds delay between module load and React hydration

Expected behavior:
Hydration should complete regardless of tab visibility.

Provide environment information

- Next.js: 16.x
- React: 19.x
- Turbopack: enabled

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

Turbopack

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

next build (local)

Additional context

Key Finding

• Pages Router + Turbopack: Has this delay
• App Router + Turbopack: Works correctly (no delay)
• Pages Router + Webpack: Works correctly (no delay)

Run the linked happyjosh/turbopack-pages-router-bug reproduction with yarn dev --turbopack, beginning with its minimal _app.tsx and console timing logs. Compare Pages Router with App Router and Webpack under a background-tab load; done means Pages Router hydration completes without waiting for the tab to become visible.