next-mdx-remote 6 drops object-valued JSX props: <Sandpack files={{…}}> compiles with zero files

Summary

Since the bump to next-mdx-remote 6.0.0 (ff889a1e), object-valued JSX attributes written in MDX no longer reach the component. <Sandpack files={{ '/App.tsx': '…' }} /> is compiled with files === {}.

This has two different symptoms depending on whether the block also sets template:

1. Hard build failure when there is no template. SandpackProvider throws Error: [sandpack-react]: without a template, you must pass at least one file, which aborts the whole static export.
2. Silent data loss when there is a template. The page builds, and the Sandpack renders with none of the authored files.

folder="…" is unaffected — those files are read from disk in the RSC and still resolve.

Impact

Symptom 1 is currently breaking downstream docs deploys. react-three-fiber's "Build documentation and deploy to GitHub Pages" has failed on every run since 2026-07-30 (its first push to master after the bump); the last green run was 2026-05-06. Example failure, on /getting-started/introduction: https://github.com/pmndrs/react-three-fiber/actions/runs/30643760945

Symptom 2 applies to this repo's own docs. Every files={{…}} example in docs/authoring/sandpack.mdx also passes template="react-ts", so they build without error and render empty — which is likely why CI here has stayed green.

Note that consumers run the published ghcr.io/pmndrs/docs:3 image via build.yml@v3, so a fix needs a new image publish to reach them.

Reproduction

git clone https://github.com/pmndrs/docs && cd docs
git clone https://github.com/pmndrs/react-three-fiber ../r3f && cp -R ../r3f/docs extdocs
pnpm install
MDX=extdocs OUTPUT=export DIST_DIR=extdocs/out BASE_PATH="" \
  HOME_REDIRECT=/getting-started/introduction \
  NEXT_PUBLIC_LIBNAME="React Three Fiber" \
  MDX_BASEURL=https://github.com/pmndrs/react-three-fiber/raw/master/docs \
  pnpm build

Error occurred prerendering page "/getting-started/introduction"
Error: [sandpack-react]: without a template, you must pass at least one file
Export encountered an error on /[...slug]/page: /getting-started/introduction, exiting the build.

The block that throws is the TypeScript example in docs/getting-started/introduction.mdx, which passes files={{ '/styles.css': …, '/index.tsx': … }} and no template.

Diagnosis

Logging the props Sandpack actually receives, at the top of src/components/mdx/Sandpack/Sandpack.tsx:

With next-mdx-remote 6.0.0 — inline files arrive empty, folder still resolves:

{"folder":null,"propsFilesKeys":[],"resolvedFileKeys":[],"template":null}
{"folder":"…/getting-started/basic-example-sandpack","propsFilesKeys":[],"resolvedFileKeys":["/index.jsx","/styles.css"],"template":null}

With next-mdx-remote 5.0.0, same source and same MDX:

{"folder":null,"propsFilesKeys":["/styles.css","/index.tsx"],"resolvedFileKeys":["/styles.css","/index.tsx"],"template":null}

Building this repo's own docs (MDX=docs) on 6.0.0 shows symptom 2 — the authored files are gone, but template keeps it from throwing:

{"folder":null,"propsFilesKeys":[],"resolvedFileKeys":[],"template":"react-ts"}

What isolates it

Source	next-mdx-remote	Result
v3 tip	6.0.0 (lockfile)	fails on /getting-started/introduction
b06e5458 (2026-05-07, pre-bump)	5.0.0	25/25 pages
v3 tip	5.0.0 (pinned)	25/25 pages

Same source at the tip passes or fails purely on the next-mdx-remote major, which points at the upgrade rather than at anything in src/.

I have not worked out which v6 change drops the attribute — whether compileMDX needs different options now, or whether this is an upstream regression worth reporting there. Happy to dig further or put up a PR if you have a preferred direction.

Environment

• pmndrs/docs v3 @ 6469729f, and b06e5458 for the passing comparison
• Node 20.19.0, pnpm 10.28.1, macOS arm64
• next-mdx-remote 6.0.0 vs 5.0.0, @codesandbox/sandpack-react 2.20.0 (unchanged across both)
• MDX under test: react-three-fiber master docs

Start with src/components/mdx/Sandpack/Sandpack.tsx and reproduce the failure using the provided pnpm build command. Compare next-mdx-remote 6.0.0 with 5.0.0 and inspect the compileMDX path, plus the examples in docs/getting-started/introduction.mdx and docs/authoring/sandpack.mdx. Done means inline files reach Sandpack, both affected cases build correctly, and the published image path is identified.