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Turbopack Dev Regression: Pages Router Page Modules Missing After _App Availability Seeding (#97664)

In Next.js 16.4.0 dev with Turbopack, Pages Router pages crash during hydration because required client modules are not included in any chunk. The regression was introduced by #97664, which seeded availability info from the _app chunk group into page chunk groups; in dev each entry has its own module graph, so availability items from _app are wrongly treated as already available, causing modules like a-page-only and b-boundary to be skipped.

highConfidence 95%Next.js Affected V16.4.0-Canary.0 Affected V16.4.0 Affected V16.5.0-Canary.2

Origin Analysis

#97664 makes every non-_app page's client chunk group start from the availability_info of the /_app chunk group. In next dev, each entry has its own module graph; the availability items from the _app graph refer to nodes that are not the same in the page graph. Specifically, a page entry pre-batch [a, Ref(b), c, Ref(d), e, index] splits into module batches where Module(c) holds references to earlier siblings a and b. The _app graph has Module(c) as an available item; when chunk_group_content processes the page graph, it marks Module(c) as available and returns Exclude, skipping its subtree, so a and b are never assigned to any chunk, leading to module factory not available during hydration.

1. Clone https://github.com/Stanzilla/next-turbopack-app-availability-repro 2. npm install 3. npm run dev (next dev --turbopack -p 3456) 4. Open http://localhost:3456/ 5. Observe hydration error: Module [project]/lib/a-page-only.js was instantiated but the module factory is not available.

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 only affects dev and restores pre-16.4.0 behavior. No production impact. If applied, ensure to remove/disable any dev-specific caching of availability info and test with the provided repro and large Pages Router apps. Rollback: revert to the original code that unconditionally uses app_availability; however that reintroduces the dev bug. For a more robust fix, consider making availability info graph-scoped or excluding only cross-graph references in chunk_group_content.