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Next.Js Build Intermittently Fails With E696 Invariant: Expected WorkUnitAsyncStorage To Have A Store During Static Export Under Load

During `next build` static export on large apps, a race condition in Next.js 16.1.6 (and canary) causes random pages to fail with `Invariant: Expected workUnitAsyncStorage to have a store` (E696). The issue occurs only under heavy CPU load, making it hard to reproduce in CI. Root cause is context loss from `workUnitAsyncStorage` when `getFlightResponse` is first touched outside the `workUnitAsyncStorage.run` scope via abort-path unwind or backpressure resume.

highConfidence 85%Next.js Affected V16.1.6

Origin Analysis

Race condition in `server/app-render/use-flight-response.js`: `getFlightResponse` memoizes the deserialized flight response per stream at first touch and reads `workUnitAsyncStorage.getStore()` from whatever async context makes that first touch. If that first touch occurs outside any `workUnitAsyncStorage.run(store, …)` scope (due to abort handler execution in the enclosing scope or backpressure resume from the consumer's `pull()`), the store is `undefined`, triggering the E696 invariant. The store is only functionally needed for `prerender-client` deferral; the throw is a context-loss tripwire.

1. Clone repro: `https://github.com/discordwell/next-e696-workunit-store-race` 2. Run `npm install` 3. Run `npm run repro` (loops `next build --webpack` under CPU spinners; set `RUNS=25` for more attempts) 4. Observe intermittent failure: `Error [InvariantError]: Invariant: Expected workUnitAsyncStorage to have a store. This is a bug in Next.js.` on random static pages during `Generating static pages` phase. Requires genuine machine-wide CPU contention.

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 is a homegrown patch not yet validated by the Next.js core team. It may mask other context-loss bugs if the store is genuinely required for other operations. Test thoroughly under load, including with `prerender-client` and `validation-client` features. If the build still fails or produces incorrect HTML, revert by removing these modifications and use the `experimental.staticGenerationRetryCount: 3` workaround until an official fix is released. Upgrading to a future Next.js version without this issue is the long-term solution.