Feature request: add an in-chat turn minimap with summaries and changed files

Summary

Please add an in-chat turn minimap / timeline to Codex VS Code and Codex Desktop chat views.

For long Codex sessions, it becomes hard to navigate previous turns, find where a file was changed, or jump back to a specific user request / assistant result. Codex Desktop appears to already have a compact left-side conversation marker/preview affordance in some surfaces, but Codex VS Code chat does not expose this in the main chat UI.

Proposed UX

Add a slim vertical timeline/minimap on the left side of the chat transcript:

• Each user turn is represented by a small marker aligned with its position in the transcript.
• Hovering a marker shows a compact preview card:
• user prompt summary
• assistant response summary
• changed files in that turn, shown as chips
• status such as running / completed / failed
• Clicking a marker scrolls the chat to that turn.
• Turns with file changes should be visually distinct.
• The feature should live inside the main chat UI, not only in a separate history viewer.

Why this matters

Codex conversations often become long because one task can include many tool calls, edits, test runs, and follow-ups. In a long chat, users need to answer questions like:

• Which turn changed this file?
• Where did Codex explain a decision?
• Where did the last successful test happen?
• Which user request started this branch of work?
• What happened before the current turn?

Today this requires manual scrolling and visual scanning, which is slow and error-prone.

Possible implementation

The app-server / thread history layer already has data that seems close to what is needed:

• Turn
• ThreadItem
• assistant/user messages
• FileChange / changed files
• turn status and timestamps

The UI could build a lightweight per-turn index from existing thread history and render it next to the transcript.

Related prior art

A third-party VS Code extension, Codex History Viewer, already advertises an opt-in Codex turn timeline with turn boundaries, summaries, running state, and file-change diffs. That suggests this is useful enough that users are building it outside the official Codex UI.

But the ideal experience is first-party and directly inside the active Codex chat view.