[Turbopack Nextjs 16]: Turbopack fails to load markdown(x) files only if `mdxRs` is set to `false`

[arunanshub]

Link to the code that reproduces this issue

https://github.com/arunanshub/nextjs-16-turborepo-mdx

To Reproduce

Reproduce dev time error

1. Start the application in dev mode (pnpm dev)
2. Go to http://localhost:3000/blog/page-1
3. Observe the crash

Reproduce build time error

1. Run pnpm build

Current vs. Expected behavior

Dev error

Turbopack version: v16.0.0-beta.0
Next.js version: v16.0.0-beta.0

Error message:

Failed to write app endpoint /(app)/blog/page-1/page

Caused by:
- Expected process result to be a module, but it could not be processed

Debug info:
- Execution of get_written_endpoint_with_issues_operation failed
- Execution of endpoint_write_to_disk failed
- Execution of <AppEndpoint as Endpoint>::output failed
- Failed to write app endpoint /(app)/blog/page-1/page
- Execution of AppEndpoint::output failed
- Execution of get_app_page_entry failed
- Execution of ProcessResult::module failed
- Expected process result to be a module, but it could not be processed

Build error

> nextjs-turbopack-mdx@0.1.0 build /home/arunb/work-related/safedep-related/safedep.io-next
> next build --turbopack

 ⚠ Invalid next.config.ts options detected: 
 ⚠     Unrecognized key(s) in object: 'conditions' at "turbopack"
 ⚠ See more info here: https://nextjs.org/docs/messages/invalid-next-config
   ▲ Next.js 16.0.0-beta.0 (Turbopack)
   - Experiments (use with caution):
     ✓ webpackMemoryOptimizations

   Creating an optimized production build ...

-----
FATAL: An unexpected Turbopack error occurred. A panic log has been written to /tmp/next-panic-d77266035bd3277a2a768b5c0e985bb8.log.

To help make Turbopack better, report this error by clicking here.
-----


> Build error occurred
Error [TurbopackInternalError]: Failed to write app endpoint /favicon.ico/route

Caused by:
- Expected process result to be a module, but it could not be processed

Debug info:
- Execution of get_all_written_entrypoints_with_issues_operation failed
- Execution of EntrypointsOperation::new failed
- Execution of all_entrypoints_write_to_disk_operation failed
- Execution of Project::emit_all_output_assets failed
- Execution of *emit_assets failed
- Execution of all_assets_from_entries_operation failed
- Execution of *all_assets_from_entries failed
- Execution of output_assets_operation failed
- Execution of <AppEndpoint as Endpoint>::output failed
- Failed to write app endpoint /favicon.ico/route
- Execution of AppEndpoint::output failed
- Execution of Project::whole_app_module_graphs failed
- Execution of whole_app_module_graph_operation failed
- Execution of *ModuleGraph::from_single_graph failed
- Execution of *SingleModuleGraph::new_with_entries failed
- Execution of Project::get_all_entries failed
- Execution of <AppEndpoint as Endpoint>::entries failed
- Execution of get_app_page_entry failed
- Execution of ProcessResult::module failed
- Expected process result to be a module, but it could not be processed
    at <unknown> (TurbopackInternalError: Failed to write app endpoint /favicon.ico/route) {
  type: 'TurbopackInternalError'
}

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Thu Jun  5 18:30:46 UTC 2025
  Available memory (MB): 15583
  Available CPU cores: 16
Binaries:
  Node: 22.15.1
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.18.2
Relevant Packages:
  next: 16.0.0-beta.0 // Latest available version is detected (16.0.0-beta.0).
  eslint-config-next: 16.0.0-beta.0
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Markdown (MDX), Turbopack

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local)

Additional context

This only occurs in Nextjs 16.0.0-beta.0. This does not happen in Nextjs 15.*. Furthermore, remark and rehype plugins don't work when mdxRs is set to true.

[arunanshub]

Nevermind I solved it by using @next/mdx@beta (16.0.0-beta.0). However, the issue of rehype/remark plugins not working with mdxRs = true is still there. Hence keeping this issue open.