fix(tui): preserve native scrollback on terminal resize

[joinmouse]

Related Issue

Related Issue

Fixes #3116

#3116

Problem

Resizing the terminal window could clear the native scrollback buffer and change the user's current scroll position.

This was especially noticeable when the user had scrolled away from the input area: resizing either the terminal width or height could unexpectedly move the
viewport to the top of the conversation.

What changed

• Preserve native terminal scrollback during terminal resize.
• Keep height changes on the differential rendering path instead of performing a full redraw.
• On width changes, clear and redraw only the active viewport rather than clearing scrollback or replaying the entire transcript.
• Preserve the existing full-redraw behavior for explicit render resets and Kitty image handling.
• Add regression tests covering:
  • Height changes without clearing scrollback.
  • Width changes without duplicating transcript history.
  • Width changes while the user is manually scrolled away from the prompt.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue (external PRs: the issue must have a maintainer's /approve).
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 3899079

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e91eef7dad

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".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[HelloWorldU]

We should not change current behaviors as it may lead to regression