@vercel/next: Next 16.2+/Turbopack functions crash at runtime: Cannot find module 'next/dist/server/lib/incremental-cache/tags-manifest.external.js'

Summary

Deploying a Next.js app on Next 16.2.x or 16.3.x (Turbopack build, the default) produces serverless functions that crash on every request at module load:

Error: Failed to load external module next/dist/compiled/next-server/app-route-turbo.runtime.prod.js:
Error: Cannot find module 'next/dist/server/lib/incremental-cache/tags-manifest.external.js'
Require stack:
- /var/task/node_modules/next/dist/compiled/next-server/app-route-turbo.runtime.prod.js
- /var/task/.next/server/chunks/[root-of-the-server]__....js
- /var/task/.next/server/chunks/[turbopack]_runtime.js
- /var/task/.next/server/app/api/<route>/route.js
- /var/task/___next_launcher.cjs

The same happens for pages via app-page-turbo.runtime.prod.js. Result: every node function returns 500; the build itself is green.

Evidence it is the function tracer, not the app

• next/dist/server/lib/incremental-cache/tags-manifest.external.js exists in the published next package for these versions (verified in local node_modules), and app-route-turbo.runtime.prod.js references it.
• Local next build completes cleanly; only the deployed functions fail, i.e. the file is dropped when the lambda's node_modules/next/dist is pruned to traced files. The .external.js modules are loaded through the Turbopack runtime's externalRequire, which the tracer evidently cannot see.
• Controlled comparison on the same commit, same project, four deploys: next 16.1.4 works; 16.2.12 and 16.3.3 both crash with the error above.
• No user-side workaround exists: outputFileTracingIncludes is not applied under Turbopack builds (build/index.js only calls collect-build-traces when the bundler is not Turbopack), and building with --webpack is not viable for apps with dependencies that rely on Turbopack's tolerance of dangling imports.

Expected

The @vercel/next builder includes the *.external.js runtime modules (at minimum next/dist/server/lib/incremental-cache/** and siblings) that Next >= 16.2 requires at runtime from its compiled turbo runtimes.

Environment

• next: 16.2.12 / 16.3.3 (broken), 16.1.4 (works)
• Build: next build (Turbopack default), deployed via git integration and CLI, identical result
• Runtime: Node 22 serverless functions

Happy to provide additional detail. Filing here since the failure is in function packaging at deploy time; if this belongs in vercel/next.js instead, please redirect.

Start in build/index.js, where collect-build-traces is only called for non-Turbopack builds, and trace the @vercel/next function packaging path. Reproduce with a Next 16.2.x or 16.3.x Turbopack deployment and inspect which next/dist/server/lib/incremental-cache/*.external.js files are included. Done means the deployed serverless function loads and serves requests without the missing-module error.