Notebook does not respect output rendering settings

[Tyrrx]

Describe the bug

When settings the output rendering to plain text the notebook still shows it as a custom component:

In Host mode the error text is not outputted as string:

When running e.g. Helmfile, which prints to std error, the output is basically not usable because it's too verbose.

Please complete the following:

Which version of .NET Interactive are you using? (In a notebook, run the #!about magic command. ):

• OS
  • [ ] Windows 11
  • [ ] Windows 10
  • [ ] macOS
  • [X] Linux (NixOS 25.05)
  • [ ] iOS
  • [ ] Android
• Browser
  • [ ] Chrome
  • [ ] Edge
  • [ ] Firefox
  • [ ] Safari
• Frontend
  • [X] Jupyter Notebook
  • [ ] Jupyter Lab
  • [ ] nteract
  • [X] Visual Studio Code
  • [ ] Visual Studio Code Insiders
  • [ ] Visual Studio
  • [ ] Other (please specify)

Screenshots

[Tyrrx]

Current workaround for applications that only write on stderr is piping stderr to stdout by appending 2>&1 | Out-Host

[jonsequitur]

I believe this behavior was changed with #3912.