[BUG] Input box collapses to zero height when typing on Termux (regression in 2.1.23)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

On Termux (Android terminal emulator), the input prompt has multiple rendering issues starting with version 2.1.23:

1. The input prompt bracket (>) is missing
2. The horizontal bars above and below the input area are collapsed together (no space between them)
3. Slash commands partially work initially, but when pressing space, the typed text disappears and the border lines collapse
4. Typed text is invisible until Enter is pressed

What Should Happen?

The input box should:

• Display the > prompt character
• Maintain proper height between the border lines
• Show typed text in real-time, including when spaces are typed

Steps to Reproduce

1. Install Claude Code 2.1.23 or later on Termux (Android)
2. Run claude
3. Observe: The > prompt is missing, the input area appears collapsed
4. Type /help - observe this partially renders
5. Press space after the slash command
6. Observe: text disappears, the two horizontal border bars collapse together
7. Press Enter - text reappears and is processed correctly

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.22

Claude Code Version

2.1.23+

Platform

Anthropic API

Operating System

Other Linux (Android/Termux)

Terminal/Shell

Other (Termux - Android terminal emulator)

Additional Information

• TERM=xterm-256color
• COLORTERM=truecolor
• Terminal reports proper dimensions via stty size and tput cols

Likely cause: The changelog for 2.1.23 mentions "Improved terminal rendering performance with optimized screen data layout" - this optimization appears to have issues with Termux's terminal emulator.

The Ink rendering engine's differential output system (lastOutput, lastOutputHeight) and the yoga layout calculations may be making assumptions about terminal behavior that don't hold on Termux.

The symptom pattern (works with slash commands, breaks on space) suggests the text measurement or height calculation returns incorrect values when the input contains space characters.