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RuntimeServerDeploymentId: Prerendered Flight Payloads Pin Build-Time Deployment Id Causing Infinite MPA Reload Loop

When runtimeServerDeploymentId is enabled and a build artifact is served under a different deployment ID, the navigation build ID embedded in prerendered flight payloads remains the build-time ID. This causes client-side skew detection (responseBuildId !== getNavigationBuildId()) to trigger an MPA fallback on every client navigation, resulting in an infinite hard-reload loop.

highConfidence 95%Next.js Affected V16.3.3 Affected V16.4.0-Canary.12

Origin Analysis

The prerendered flight payload's `b` field (navigation build ID) is serialized at build time with the build-time deployment ID. At runtime, `data-dpl-id` and dynamic response headers correctly use the runtime deployment ID, but the prerendered payload is not updated, so the client receives a mismatched navigation build ID and falls back to full document navigations.

1. Build a Next.js app with `NEXT_DEPLOYMENT_ID=dpl_aaaaaaaaaaaaaaaa` and `experimental.runtimeServerDeploymentId` enabled. 2. Start the server with `NEXT_DEPLOYMENT_ID=dpl_bbbbbbbbbbbbbbbb` using the same build artifact. 3. Open a fully prerendered page and click a `<Link>` to a dynamic page. 4. Observe in the Network tab that a full document navigation occurs instead of a client-side RSC navigation. Repeat the click; the hard reload never recovers. 5. Control: restart with the same deployment ID as build (`dpl_aaaaaaaaaaaaaaaa`) and the same click performs a client-side navigation.

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

The regex-based replacement may inadvertently modify other `"b":"..."` strings in the HTML if they appear outside the Flight payload (e.g., in user-generated content). It should be scoped to the Flight data script tags or use a placeholder during build. Additionally, ensure `getDeploymentId()` is available in all server entry points. Rollback: set `NEXT_DEPLOYMENT_ID` to the build-time ID or disable `runtimeServerDeploymentId`.