draftMode not accurate in middleware with nodejs runtime

Link to the code that reproduces this issue

https://github.com/erzr/nextjs-middleware-draft-mode

To Reproduce

• Check out linked repro
• Visit /api/preview which enables draft mode
• Observe that redirect happens but response headers contain x-draft-mode = disabled
• Visit /?draft=true which triggers middleware to set draft mode to true
• Observe the error Invariant: previewProps missing previewModeId this should never happen
• Comment out runtime from middleware
• Observe this functionality works as expected

Current vs. Expected behavior

When following steps, I expect (await draftMode()).isEnabled to be accurate and to be able to enable draft mode from middleware without error.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:49 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6000
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 22.17.0
  npm: 10.9.2
  Yarn: 4.9.1
  pnpm: 10.14.0
Relevant Packages:
  next: 15.4.2-canary.29 // Latest available version is detected (15.4.2-canary.29).
  eslint-config-next: N/A
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.9.2
Next.js Config:
  output: N/A

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

Draft Mode

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

next dev (local), Vercel (Deployed)

Additional context

Seems like some environment variables might be missing? When I print out process.env I see some _NEXT prefixed variables not present in nodejs runtime but present in edge runtime.

Run the linked reproduction and compare the /api/preview and /?draft=true flows with the middleware using the Node.js runtime versus the Edge runtime. Trace how draft mode state and environment variables reach middleware, then verify that draftMode().isEnabled is accurate and the previewProps missing previewModeId error no longer occurs.