Chat surfaces should use rich-text-style message rendering

[isCopyman]

Summary

Chat/message surfaces in Maestro currently behave like Markdown document previews rather than rich-text-style chat messages.

This causes message structure and display math to render incorrectly in normal chat use cases, even though Markdown file preview behaves correctly as a document surface.

Current behavior

On chat surfaces such as AI Terminal, group chat, and mobile message history:

• Single newlines are merged too aggressively, so multi-line messages can be visually flattened into a single paragraph.
• Messages containing isolated display math such as $$x+y$$ on its own line can render as visually cramped/left-aligned content instead of a clear centered block formula.
• User messages can be rendered with Markdown formatting in some chat surfaces, but the plain/raw text toggle is only available for assistant output, which is inconsistent.

At the same time, Markdown file preview currently looks correct and should keep standard Markdown document semantics.

Why this is a problem

Chat is not the same as Markdown document preview.

For chat/message surfaces, users expect:

• line structure to be preserved
• display math to look like display math
• rich-text-style rendering by default
• raw/plain-text inspection to be available consistently when formatting is applied

Today the current behavior makes formula-heavy or structured chat content harder to read than it should be.

Suggested direction

Split rendering behavior by surface:

• Chat/message surfaces should use a chat-oriented rich-text Markdown preset
• Document/file preview surfaces should remain standard Markdown

For chat surfaces specifically:

• Preserve single newlines as visible line breaks
• Treat line-isolated $$...$$ as display math and render it as centered block content
• Keep Markdown enhancements such as code blocks, links, lists, tables, and math
• Expose plain/raw text viewing consistently for both user and assistant messages

For document surfaces:

• Keep the current standard Markdown behavior for .md preview/editor views

Notes

• This seems closer to the behavior users expect from GitHub comments / AI chat UIs than the current document-style Markdown behavior.
• This issue is about chat rendering semantics, not about rewriting the entire Markdown system.

[isCopyman]

The style of Google AIStudio or GitHub could be considered.