Codex desktop: native source line numbers with syntax highlighting in chat code blocks and diffs

What variant of Codex are you using?

Codex desktop app on macOS.

What feature would you like to see?

Please support native line-number gutters alongside syntax highlighting for code snippets and diffs in assistant chat responses, including an explicit starting source-line number.

When reviewing a PR, the assistant referred to specific source lines but displayed a diff without visible line numbers. Asking for numbers led to a plain-text block that lost syntax highlighting. Asking for both led to fake line numbers embedded as TypeScript comments. Those comments are visually distracting, pollute copied code, and should not be necessary in a coding tool.

Desired behavior:

• Preserve language syntax highlighting while displaying source line numbers in a separate gutter.
• Allow snippets to start at their actual source line, rather than always at 1.
• Support old/new line numbers for diffs alongside addition/deletion highlighting.
• Keep line numbers and display annotations out of copied code.
• Let the assistant invoke this rendering directly so users do not need to open another view merely to follow a line-specific explanation.

Additional information

This is about code and diff excerpts in conversational answers, not just the standalone file editor or review panel. The current experience is frustrating during code review: users should not have to choose between readable syntax highlighting and usable line references. In my experience Claude Code handles this presentation better; Codex should offer an equally clear native display instead of plain-text or comment-based workarounds.

The issue names no files, tests, or entry points. Begin by locating the Codex desktop chat rendering paths for code blocks and diffs, then determine how copied content is produced. Done means syntax highlighting, configurable source-line starts, diff line numbers, and clean copied code all work in conversational responses.