bug: Chat message view sometimes drops newline characters

[novmikvis]

In the chat UI, assistant messages returned from the API are rendered as a single paragraph with all line breaks removed. The same message shows correct \n newlines in the Edit message dialog and when copied to the clipboard, so the issue is limited to how the chat bubble renders text.

Expected result

Newlines (\n) are preserved and rendered as visual line breaks in the chat bubble, matching what appears in the Edit message dialog and when copied.

Actual result

The chat bubble collapses all single newlines into spaces and renders one continuous paragraph.

The Edit message dialog shows the correct line breaks.

[github-actions]

Found 3 possible duplicate issues: 1. #849 2. #377 3. #4039

[LazyYuuki]

Hi @novmikvis can I check with you the version you are using? is it 0.7.1?

[novmikvis]

@LazyYuuki I am using Jan v0.7.1 and Windows 11 24H2
Could repeat with API gpt-5-mini, claude-sonnet-4-5-20250929 and gemini-2.0-flash-001
Locally with Gemma-3-12b-it-quat-UD-Q6_K_XL

Strangely i couldn't repeat with gpt-oss-20b0mxfp4 (it kept using - instead of • as described in system prompt)

I've done more tests with gpt-oss and able to reproduce the behavior with this prompt:

You are a newline probe. Reply in PLAIN TEXT ONLY (no Markdown, no code fences, no extra spaces). 
Return EXACTLY the text between the markers, preserving every character, including newlines.
Do not add or remove anything before, between, or after the markers.

<<<BEGIN>>>
[01] alpha
[02] beta
[03] gamma

[05] epsilon
[06] zeta
<<<END>>>

Interestingly the problem presents itself only in "answer" part of the message, but still, inside the tags it is formated correctly and incorrectly at the same time 🤔

Tell me if I need to do some more tests