[BUG] Enlarging terminal window causes duplicate Claude UI instances to stack vertically

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Body:

## Description

When resizing (enlarging) the terminal window while Claude Code is running, the TUI does not redraw in place — instead it
renders a new copy of the UI below the existing one, causing multiple stacked instances to appear on screen.

## Expected Behavior

The UI should redraw in place when the terminal is resized, replacing the old layout cleanly.

Enlarging the window causes duplicate copies of the Claude Code UI to stack vertically on screen. Each resize adds another copy
underneath the previous one.

## Observations

• Only occurs when enlarging the window (not confirmed on shrink)
• Terminal correctly forwards the resize signal — stty size reports updated dimensions immediately after resize, confirming

SIGWINCH propagates

• The issue is on Claude Code's side: it does not redraw in place after receiving the signal
• Functionally the session still works, but the visual stacking makes the interface confusing

## Steps to Reproduce

1. Open Terminal.app on macOS
2. Start claude CLI
3. While Claude Code is running, enlarge the terminal window
4. Observe duplicate UI instances stacked vertically

## Environment

• OS: macOS (Darwin 25.3.0)
• Terminal: Terminal.app
• Shell: zsh
• Claude Code: latest

## Related

• #16578 — similar ANSI cursor movement / redraw issue in long conversations (closed as not planned)

What Should Happen?

Expected Behavior

The UI should redraw in place when the terminal is resized, replacing the old layout cleanly.

Error Messages/Logs

Steps to Reproduce

## Steps to Reproduce

1. Open Terminal.app on macOS
2. Start claude CLI
3. While Claude Code is running, enlarge the terminal window
4. Observe duplicate UI instances stacked vertically

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

latest

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_