fix: persist cacheControl for Pages Router ISR entries in FileSystemC… - #100495

What?

Fixed ISR cache lifetime persistence for Pages Router pages using the default FileSystemCache implementation.

Why?

Pages Router ISR cache entries did not persist their revalidation interval to disk. After restarting the server, the cache lifetime defaulted to 1 second instead of the configured revalidate value.

As a result, previously generated pages could be treated as stale immediately after a restart, and the expected Cache-Control header was not preserved.

This complements #99289, which addressed the same issue for the App Router, and covers the missing Pages Router case. See also #99288.

How?

• Persisted the cache lifetime when writing Pages Router cache entries to disk.
• Restored the persisted cache lifetime when reading cache entries from disk.
• Added a Pages Router test case to test/production/app-dir/isr-cache-control-restart/ to verify cache behavior after a server restart.

Before the fix, the test failed because the first request after restarting the server returned a STALE cache status instead of HIT.

Verified that all 5 tests pass with both Turbopack and webpack using:

• pnpm test-start-turbo
• pnpm test-start-webpack