Unable to use custom renderers on server

[Inbestigator]

Link to the code that reproduces this issue

https://github.com/Inbestigator/rr-next-repro

To Reproduce

1. Start the application in dev
2. Go to /
3. View the console output

Current vs. Expected behavior

Currently Next seems to be causing React.__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE to be undefined, instead it should be an object like this:

{
  H: null,
  A: null,
  T: null,
  S: null,
  V: null,
  actQueue: null,
  isBatchingLegacy: false,
  didScheduleLegacyUpdate: false,
  didUsePromise: false,
  thrownErrors: [],
  getCurrentStack: null,
  recentlyCreatedOwnerStacks: 0,
}

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.0.0: Wed Aug 27 20:24:40 PDT 2025; root:xnu-12377.1.9~17/RELEASE_ARM64_T8122
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 24.1.0
  npm: 11.3.0
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 15.5.1-canary.30 // Latest available version is detected (15.5.1-canary.30).
  eslint-config-next: N/A
  react: 19.1.1
  react-dom: 19.1.1
  typescript: 5.9.2
Next.js Config:
  output: N/A

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

Server Actions

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

next dev (local), next start (local), Vercel (Deployed), Other (Deployed)

Additional context

react-reconciler requires React.__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE to work.

This means that any custom renderers (like my Discord bot component renderer) running on the server are incapable of working.