TUI: add a right-side user prompt navigator for long conversations

What variant of Codex are you using?

Codex CLI / TUI

What feature would you like to see?

Add an optional right-side conversation navigator that lists the user prompts in the current session and lets users jump directly to any prompt/response turn.

A possible wide-terminal layout:

┌──────────── Conversation ────────────┬──── Prompt navigator ────┐
│ Codex output, code, tool logs...      │ 01 Initialize project    │
│                                      │ 02 Analyze data delay     │
│                                      │ 03 Fix gripper handling   │
│                                      │ 04 Check causal leakage ← │
│                                      │ 05 Adjust replan          │
└──────────────────────────────────────┴───────────────────────────┘

Suggested behavior:

• Show a numbered, one-line preview of every user prompt in the current transcript.
• Highlight the turn currently visible in the main transcript.
• Allow mouse click or keyboard selection to jump to a turn.
• Provide search/filter over user prompts.
• Keep navigation read-only by default: jumping should not roll back, edit, or fork the conversation.
• Use a distinct action, such as e, to edit/backtrack from a selected historical prompt.
• Preserve the selected turn after resizing or reopening a resumed session.
• Allow the panel to be toggled, for example with /navigator or a shortcut.

For narrow terminals, the same feature could appear as a searchable overlay similar to the transcript view instead of consuming a permanent side panel.

Why is this useful?

Long Codex sessions often contain extensive command output, code patches, logs, and explanations. The user prompts are the natural section headings of the session, but today reviewing an earlier section requires manual scrollback, terminal text search, or repeated prompt-by-prompt backtracking.

A visible prompt index would make long sessions much easier to scan and would provide clearer boundaries between tasks. It would be especially useful for debugging, robotics/software development, and other workflows where a single session may contain many large tool outputs.

Related issues

• #21732 proposes keyboard shortcuts to jump between user prompts in the CLI transcript.
• #20651 proposes a conversation turn navigator for Codex Desktop.
• #17879 requests clearer visual distinction between user and assistant messages in the TUI.

This request focuses specifically on a persistent or toggleable visual prompt navigator for the CLI/TUI, complementing keyboard-only navigation.