Bundling fails for package `bknd` in turbopack

Link to the code that reproduces this issue

https://github.com/shishantbiswas/bknd-next-turbopack-bundling-issue

To Reproduce

1. Install bknd package

bun install bknd

2. Run the production build in turbopack using

bun run build

Current vs. Expected behavior

Current behavior:

$ next build
▲ Next.js 16.3.5 (Turbopack)
✓ Running next.config.ts took 9ms
- Experiments (use with caution):
  ⨯ turbopackMinify

  Creating an optimized production build ...

-----
FATAL: An unexpected Turbopack error occurred. A panic log has been written to /var/folders/x_/4f5ssykd6pd3ztqqsvpt_rbc0000gn/T/next-panic-7296c7debb1ce282673c45bda85d5f5c.log.

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


> Build error occurred
Error [TurbopackInternalError]: Failed to write app endpoint /page

Caused by:
- expected chunkable module for async reference

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 output_assets_operation failed
- Execution of <AppEndpoint as Endpoint>::output failed
- Failed to write app endpoint /page
- Execution of AppEndpoint::output failed
- Execution of Project::client_chunking_context failed
- Execution of *get_client_chunking_context failed
- Execution of get_global_module_id_strategy failed
- expected chunkable module for async reference
    at <unknown> (TurbopackInternalError: Failed to write app endpoint /page) {
  type: 'TurbopackInternalError',
  location: undefined
}
error: script "build" exited with code 1
```

Expected behavior:
Note: achieved using webpack build 

```sh
$ next build --webpack
▲ Next.js 16.3.5 (webpack)
✓ Running next.config.ts took 9ms

  Creating an optimized production build ...
⚠ Production code optimization has been disabled in your project. Read more: https://nextjs.org/docs/messages/minification-disabled
✓ Compiled successfully in 4.9s
✓ Finished TypeScript in 753ms    
✓ Collecting page data using 7 workers in 255ms    
[INF] 2026-09-12 09:04:53 Using node-sqlite connection file:data.db
[LOG] 2026-09-12 09:04:53 App built
✓ Generating static pages using 7 workers (4/4) in 327ms
✓ Collecting build traces in 2.2s    
✓ Finalizing page optimization in 2.2s    

Route (app)
┌ ○ /
├ ○ /_not-found
├ ƒ /admin/[[...admin]]
└ ƒ /api/[[...bknd]]


○  (Static)   prerendered as static content
ƒ  (Dynamic)  server-rendered on demand
```

### Provide environment information

```bash
Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.6.0: Fri Jul 31 19:11:03 PDT 2026; root:xnu-12377.161.14~5/RELEASE_ARM64_T8132
  Available memory (MB): 16384
  Available CPU cores: 10
Binaries:
  Node: 26.4.0
  npm: 11.17.0
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.3.5 // Latest available version is detected (16.3.5).
  eslint-config-next: N/A
  react: 19.2.8
  react-dom: 19.2.8
  typescript: 5.9.3
Next.js Config:
  output: N/A
```

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

Turbopack

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

next build (local)

### Additional context

I was trying to create a minimal example for bknd using nextjs the dev mode ran fine without and hitches but a local production build fails the moment it begins

Start with the linked bknd-next-turbopack-bundling-issue reproduction and run bun install bknd followed by bun run build. Compare the failing Turbopack next build with the successful next build --webpack, focusing on the reported expected chunkable module for async reference error. Done means the production Turbopack build completes successfully.