TUI transcript scrolling can redraw above itself in long sessions

What version of Codex is running?

codex-cli 0.125.0

What subscription do you have?

_No response_

Which model were you using?

_No response_

What platform is your computer?

macOS (Darwin 25.1.0 arm64), terminal: iTerm.app 3.7.0beta1, TERM=xterm

What issue are you seeing?

In long interactive Codex TUI sessions, scrolling upward through earlier transcript/history is unstable. Instead of simply revealing older content, the transcript appears to redraw or "scroll above itself."

The result is that reviewing earlier messages in a long session becomes unreliable and hard to follow.

This seems related to, but not identical with:

• #18528 (iTerm2 cannot scroll up in interactive Codex session, including with --no-alt-screen)
• #10591 (TUI: Skill picker scrolls with main viewport during history insertion)

This report is about the main transcript/history area itself rather than popup corruption.

What steps can reproduce the bug?

1. Open iTerm on macOS.
2. Run codex.
3. Generate enough output to require significant scrolling.
4. Try to scroll upward through earlier transcript/history in the TUI.
5. Observe that the transcript scroll/redraw behavior is unstable and can appear to render above itself instead of just moving the viewport upward.

What is the expected behavior?

Scrolling upward through long transcript history should be stable and should simply reveal older content without redraw corruption, shifting, or self-overlap.

Additional information

• Reproduced in the Codex TUI on macOS in iTerm.
• If useful, I can provide a screen recording.