Feature request: role-based styling for user messages in Codex app conversation view

What variant of Codex are you using?

app

What feature would you like to see?

Codex app conversations become hard to scan in long threads because user messages are not visually distinct enough from agent output and tool/progress items.

Please add first-class role-based styling for user messages in the Codex app conversation view:

• distinct user message background or left accent bar
• optional "jump to previous/next user message"
• Appearance setting for userMessage / agentMessage semantic colors
• preserve accessibility contrast in light and dark themes

This should be app-side only; app-server already exposes ThreadItem types such as userMessage and agentMessage.

Additional information

_No response_