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CacheComponents: Page Past Its Expire Returns 500 Due To Unstable_cache Skipping Resume Data Cache

When a static route's cache entry passes its `expire` time, Next.js sets `isOnDemandRevalidate = true` for the blocking regeneration. This causes `unstable_cache` to skip reading from the cache entirely, including the prerender resume data cache that was populated during the prospective prerender pass. As a result, the final pass fails with `NEXT_STATIC_GEN_BAILOUT` and returns HTTP 500.

highConfidence 85%Next.js Affected V16.3.4 Affected V16.3.8 Affected V16.4.0 Affected V16.5.0-Canary.3

Origin Analysis

In `app-page-runtime.js` (or `app-page.ts`), the condition `if (previousIncrementalCacheEntry?.isStale === -1) { isOnDemandRevalidate = true; }` incorrectly marks an expired entry as an on-demand revalidation. This flag causes `unstable_cache` to bypass all cache reads, including the resume data cache, leading to missing data during the blocking regeneration.

1. Clone the reproduction repo: `git clone https://github.com/tdejager/next-on-demand-unstable-cache-bailout-repro && cd next-on-demand-unstable-cache-bailout-repro && pnpm install` 2. Run `./repro.sh` which builds the app, then runs `next start` twice: control (fresh build) and aged (mtimes set to 30 minutes ago). 3. Observe that the aged run returns HTTP 500 on the first request with `NEXT_STATIC_GEN_BAILOUT` error, while control returns 200.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

This change may affect other invalidation scenarios where `isStale === -1` is expected to trigger on-demand revalidation semantics. It should be thoroughly tested with CDN/custom cache handlers and concurrent requests. Rollback: revert the condition to its original form if any regressions appear, or apply the alternative patch of removing the `isOnDemandRevalidate` condition in `unstable_cache` (less targeted). Also note that this fix does not address potential similar issues in `patch-fetch` or nested `use cache` if they also check the same flag; further testing is required.