tui: allow forward navigation in backtrack preview

[slkzgm]

Fixes #9058

Summary

When the transcript backtrack preview is armed (press Esc), allow navigating to newer user messages with the → arrow, in addition to navigating backwards with Esc/←, before confirming with Enter.

Changes

• Backtrack preview navigation: Esc/← steps to older user messages, → steps to newer ones, Enter edits the selected message (clamped at bounds, no wrap-around).
• Transcript overlay footer hints updated to advertise esc/←, →, and enter when a message is highlighted.

Related

• WSL shortcut-overlay snapshot determinism: tui: stabilize shortcut overlay snapshots on WSL #9359

Testing

• just fmt
• just fix -p codex-tui
• just fix -p codex-tui2
• cargo test -p codex-tui app_backtrack::
• cargo test -p codex-tui pager_overlay::
• cargo test -p codex-tui2 app_backtrack::
• cargo test -p codex-tui2 pager_overlay::

[github-actions]

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[slkzgm]

I have read the CLA Document and I hereby sign the CLA

[etraut-openai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Hooray!

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[slkzgm]

Thanks @etraut for resolving conflicts, much appreciated.

I pushed a small follow-up commit on top to fix the forward-step highlight path and keep the WSL helper import gated under cfg(not(test)).

[joshka-oai]

Let’s split this PR into two parts.

The WSL-related issue is orthogonal to the Esc / backtrack behavior and would be better addressed in a separate change. Keeping them together makes the scope harder to reason about and review, and they likely have different root causes and fixes.

If we can isolate the backtrack navigation changes here and handle the WSL behavior independently, that will make both paths clearer and easier to validate.

[slkzgm]

Thanks! Split done as suggested: this PR now contains only the backtrack navigation + transcript overlay hints. The WSL snapshot determinism change is in #9359 (tracking issue: #9361).

[etraut-openai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

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[joshka-oai]

LGTM - thanks for the PR (resolved the merge conclict and will ship)