[BUG] macOS Terminal.app faulty in-place updates when "Unicode East Asian Ambiguous characters are wide" theme setting is enabled

Environment

• Platform (select one):
• [x] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.83 (Claude Code)
• Operating System: macOS 15.6
• Terminal: Terminal.app

Bug Description

When "Unicode East Asian Ambiguous characters are wide" is enabled, Terminal.app fails to properly display the claude code CLI. Instead of repainting the text in-place, it will continuously append the contents to the terminal.

The theme I was using had this property checked by default and it caused to CLI to be almost unusable.

Steps to Reproduce

1. Open Terminal.app
2. Enable Unicode East Asian Ambiguous characters are wide for your current theme.
3. Settings -> Advanced -> "Unicode East Asian Ambiguous characters are wide" (at the bottom)
4. Relaunch your Terminal window
5. Run claude

Expected Behavior

The CLI updates are in place

<img width="842" height="542" alt="Image" src="https://github.com/user-attachments/assets/aec35f0a-bc33-4b5c-b5e4-8477d5b2e8ed" />

Actual Behavior

<img width="842" height="542" alt="Image" src="https://github.com/user-attachments/assets/a4de81f1-03f3-4c7e-9325-427c10a0859d" />

(every keystroke a new dashed line is appended)

Additional Context

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