VS Code Codex chat code blocks lose syntax highlighting / render monochrome on latest VS Code

Description

In the latest VS Code with the latest Codex extension, fenced code blocks in the Codex chat panel are no longer syntax-highlighted and render almost entirely in a single white/gray color.

The normal VS Code editor still has correct syntax highlighting, so the problem appears isolated to the Codex chat/webview renderer rather than VS Code's editor tokenization or the language extension.

Reproduction

1. Open the Codex extension in VS Code.
2. Ask: show me a sample java code.
3. Codex correctly detects the fenced block as Java (the Java language label is shown).
4. Observe that keywords, types, strings, methods, etc. are all rendered nearly the same white/gray color instead of normal syntax colors.
5. Compare with code in the normal VS Code editor: editor syntax highlighting works correctly.

Expected behavior

Codex chat code blocks should have syntax highlighting according to the detected language (for example, public, class, strings, types, and methods should receive differentiated token colors).

Actual behavior

The language is detected correctly, but the code inside the Codex chat code block is essentially monochrome.

Environment

• OS: Windows
• VS Code: latest version as of 2026-08-30
• Codex VS Code extension: latest version as of 2026-08-30
• Reproduced with Java code blocks
• Regular editor syntax highlighting: working
• Codex chat syntax highlighting: broken

Notes

This looks like a Codex webview / fenced-code syntax-highlighting regression. The issue is especially visible when comparing the Codex chat panel side-by-side with the editor: the editor has full token coloring while the Codex code block does not.

I can provide a screenshot showing the side-by-side behavior if needed.

Reproduce the issue in the Codex VS Code chat panel with a fenced Java code block, then inspect the extension's webview and fenced-code rendering path. Compare its language detection and highlighting behavior with the normal editor; done means Java keywords, types, strings, and methods render with differentiated syntax colors in chat.