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Runtime-Rendered Fully Static Pages On PPR Routes Are Not Persisted With .Rsc, Causing Perpetual Cache Misses

When partial prerendering (PPR) is enabled, runtime-rendered pages with no postponed state are written to the file-system cache without an .rsc file, but the read path requires .rsc for such entries, leading to cache MISS on every request after eviction from memory.

highConfidence 95%Next.js Affected V16.3.4 Affected V16.4.0-Canary.19

Origin Analysis

Inconsistent conditions between write and read paths in the file-system cache: FileSystemCache.set() only writes .rsc when !ctx.isRoutePPREnabled, while FileSystemCache.get() expects .rsc for APP_PAGE entries when !ctx.isFallback && (!ctx.isRoutePPREnabled || meta.postponed == null). This asymmetry causes fully static runtime-rendered PPR pages to be treated as cache misses.

1. Create a Next.js app with PPR enabled and a dynamic route /[slug] with generateStaticParams returning ['built'] and cacheComponents: true. 2. Build and start the server with cacheMaxMemorySize: 0 to force file-system cache reads. 3. Request /runtime (not prerendered) multiple times; observe x-nextjs-cache: MISS on every request and no .rsc file written. 4. Apply the proposed one-line fix to FileSystemCache.set() and repeat; observe subsequent requests return HIT and .rsc is written.

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 write .rsc files for PPR routes that are fully static, which should be safe as the read path already expects them. However, if a partially prerendered page (with postponed state) ever appears with postponed null due to a bug, the .rsc could be written incorrectly. It is recommended to monitor for any unexpected caching of dynamic content. Rollback: revert the condition to the original if regression occurs; the old behavior (no disk read for runtime-rendered static PPR entries) is preferable to serving incorrect cached data.