docs: correct the claim that Turbopack ignores outputFileTracingIncludes

[jouwdan]

MEI-134's premise was wrong, and it was mine. This corrects the record rather than implementing the ticket.

The claim

Two documents said, in different words, that outputFileTracingIncludes never executes:

outputFileTracingIncludes cannot put them back while next build defaults to Turbopack, for which Next skips trace collection entirely. — docs/vercel.md

standalone makes Vercel's builder read .next/next-server.js.nft.json, and Next skips the tracing that writes it whenever the bundler is Turbopack — docs/development.md

The reasoning came from next/dist/build/index.js:1627, which is real:

if (bundler !== _bundler.Bundler.Turbopack && !isGenerateMode && !buildTracesPromise) {
    buildTracesPromise = collectBuildTraces(...)
}

collectBuildTraces is skipped. The conclusion does not follow — Turbopack emits the .nft.json files and applies the include globs on its own side. The option is handled in next/dist only by collectBuildTraces, which is exactly why reading that far is misleading.

The measurement

Against a real Turbopack build of apps/community (chunkLoadingGlobal: "TURBOPACK"), not argued from source:

file	covered by the '/**' key?	@swc/helpers entries	under esm/
next-server.js.nft.json	no	3	0
server/app/admin/log/page.js.nft.json	yes	1318	324

The covered one also lists the package's LICENSE — a file no tracer would ever follow. That is the glob, not tracing.

What this changes

Nothing in the build. The glob in apps/community/next.config.mjs is load-bearing: it is the only thing putting @swc/helpers/esm into the standalone tree, and without it self-hosted and Docker boards fail at request time with Cannot find module '@swc/helpers/esm/…'. MEI-120's gate on its pinned version guards something real. Both stay exactly as they are — which is the point of correcting this, since the ticket as filed proposed removing them.

Two consequences for prose:

• The explanation for the missing migration .sql files on Vercel was wrong. They are absent because nothing imports them and nothing lists them, not because the mechanism is unavailable. MEI-133's schema check stands on its own arguments — lock contention across cold starts, function timeouts — which were always the better ones.
• Why output: 'standalone' broke the Vercel build is now recorded as unestablished. The failure was real and reproducible; the mechanism given for it does not hold, and I could not determine the true one without a Vercel build.

The positive fact is written down beside the glob it explains, because reading next/dist alone leads to the wrong conclusion — it did so twice.

Still open

Whether Turbopack emits .nft.json when output is unset, which is today's Vercel configuration. Everything measured here came from a build with output: 'standalone', and the emission condition lives in the Rust binary. If it turns out nft files are not emitted there, the glob is inert on Vercel specifically while remaining load-bearing for Docker and self-hosting. Recorded on MEI-134; one next build with VERCEL=1 settles it.

Verification

docs:links:check, docs:index:check and site:docs:check all pass. Documentation only — no code changes.

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