[BUG] Fenced code blocks in assistant messages render without syntax highlighting (VS Code extension)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Fenced code blocks in assistant message text render as flat monospace with a
per-line gray background and no syntax highlighting, even when the fence carries a
correct language tag (` `ts , `js , `html , `tsx `).

The gray background hugs each line's text width rather than spanning the full block
width, which reads like inline-<code> styling being applied to a <pre> element.

By contrast, code shown in Edit / Write tool results in the same panel renders
with full syntax highlighting and diff coloring. So a highlighter is clearly present
in the webview — it just doesn't appear to be applied to markdown code fences in
message text.

Screenshot:

<img width="805" height="434" alt="Image" src="https://github.com/user-attachments/assets/0573332c-9cd9-4620-90e1-626555d9d8e2" />

What Should Happen?

Fenced code blocks in assistant messages get the same syntax highlighting as code in
tool results.

Error Messages/Logs

Steps to Reproduce

1. Open the Claude Code panel in VS Code.
2. Ask any question whose answer contains a multi-line fenced code block with a

language tag — e.g. "explain this PR with code examples", or simply
"show me a TypeScript function in a code block".

1. In the same conversation, have Claude edit a file so an Edit tool result appears.
2. Compare the two renderings: the tool-result code is highlighted; the code block in

the message text is not.

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.219

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Steps to reproduce

1. Open the Claude Code panel in VS Code.
2. Ask any question whose answer contains a multi-line fenced code block with a

language tag — e.g. "explain this PR with code examples", or simply
"show me a TypeScript function in a code block".

1. In the same conversation, have Claude edit a file so an Edit tool result appears.
2. Compare the two renderings: the tool-result code is highlighted; the code block in

the message text is not.

Impact

Long code-heavy explanations (PR walkthroughs, before/after diffs, design writeups)
are hard to read in the panel. The workaround is to have Claude write the explanation
to a .md file and open it in the editor, which defeats the point of explaining
in-chat.

Notes

• The webview-vs-native-renderer split above is inferred from the behavior difference,

not from reading the extension source — treat it as a hypothesis, not a diagnosis.

• If the flat style is deliberate rather than a bug, please read this as a feature

request for opt-in highlighting.