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A Stale "Use Cache" Hit Replaces Its Own Entry In The Resume Data Cache With The Background Revalidation, So Dev Reports Uncached Data And The Runtime Prefetch Loses The Entry

When a request receives a stale cached entry from a "use cache" function, the background revalidation incorrectly replaces the saved entry in the Resume Data Cache with the pending result of the regeneration. This leads to dev-time "uncached data" errors on validation renders and in production to runtime prefetch/RSC responses missing or mixing cache versions when using cacheComponents and partialPrefetching.

highConfidence 95%Next.js Affected V16.3.5 Affected V16.3.8 Affected V16.4.0 Affected V16.5.0-Canary.3

Origin Analysis

The background revalidation calls saveToResumeDataCache with the pending result from the cache handler, overwriting the already-stored cloned stale entry in the request's Resume Data Cache, causing subsequent renders in the same request to await the regeneration or miss the entry.

1. Clone https://github.com/giovannetti-eric/next-use-cache-stale-dev-validation-repro and run `pnpm install`. 2. Run `pnpm repro` for dev scenarios (builtin, control, custom) to observe uncached data errors on validation renders after a stale hit. 3. Run `pnpm repro:prod` to observe missing/mixed greeting copies in RSC responses with partialPrefetching enabled. 4. The issue reproduces on Next.js 16.3.5, 16.3.8, 16.4.0, and 16.5.0-canary.3.

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 one-line change assumes the stale entry was already cloned into the Resume Data Cache before the background revalidation starts; it is safe for the hit path. However, if a custom cache handler or a future code path skips the initial clone, the request could be left without a Resume Data Cache entry. Rollback: restore the original `saveToResumeDataCache` call. Upgrade impact: this is a hotfix not yet in an official release; test thoroughly with custom cache handlers (especially those that read Date.now() in get) and with partialPrefetching enabled, as the tiered handler's additional background get calls may still affect validation renders (workaround: set HANDLER_AGE_CHECK=false).