bug: unknown text/* mime types rendered as plain text with no distinction

[rgbkrk]

When a cell output contains an unknown text/* mime type (e.g. text/snazzy), the frontend renders it as plain text — identical to text/plain. There's no visual indication that it's a different media type.

Reproduction

from IPython.display import display
display({"text/snazzy": "hello from a custom media type"}, raw=True)

The output renders as plain text with no distinction from text/plain.

Expected behavior

Either:

• Show the mime type as a label/badge so the user knows it's not text/plain
• Or don't render unknown text/* types at all (only render known types like text/plain, text/markdown, text/html)

Context

Found while testing custom media types through the MCP server. The MCP side can handle text/snazzy with custom formatting, but the app treats all text/* identically.

Likely a text/* wildcard match in the output renderer.