[BUG] in text rendering/measurement code that doesn't properly handle edge cases in string segmentation

Environment

• Platform (select one):
• [x] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.98
• Operating System: Windows 11, WSL2, Ubuntu 22.04 24.04.3 LTS
• Terminal: Bash 5.2.21(1)-release

Bug Description

Environment:

Tool: @anthropic-ai/claude-code CLI
Node versions tested: v22.18.0 and v20.19.4
OS: Linux (based on file paths)
Frequency: Multiple crashes per day

Error Description:

Consistent TypeError when the CLI attempts to render text in the terminal. The error occurs in the string width measurement function during text layout calculations.
Error Message:
ERROR Cannot read properties of undefined (reading 'codePointAt')
file:///.../node_modules/@anthropic-ai/claude-code/cli.js:809:28790
Stack Trace Pattern:
The error consistently occurs in:

B3 function (string width measurement)
SP2.stringIndexToDisplayWidth
SP2.getPositionFromOffset
During text rendering/wrapping operations

Key Details:

Error persists across Node.js versions (20 and 22)
Occurs during normal usage and when trying to use /bug command
The text segmentation appears to produce undefined values that the width measurement function cannot handle
Clean reinstall did not resolve the issue

Impact:

Tool is unusable due to frequent crashes
Cannot submit bugs through the /bug command as it triggers the same error
Blocking normal development workflow

Reproduction:
Crashes occur during regular usage. Even attempting to submit a bug report via /bug triggers the crash.
Attempted Solutions (all unsuccessful):

Downgraded from Node 22 to Node 20
Clean npm cache and reinstall
Fresh installation of claude-code

Steps to Reproduce

1. Install claude-code CLI: npm install -g @anthropic-ai/claude-code
2. Run claude-code in terminal with any command or prompt
3. During normal interaction, the CLI crashes (occurs multiple times per day)
4. Alternative: Try to submit a bug using /bug command - this also triggers the crash

Expected Behavior

• The CLI should render text properly in the terminal and allow normal interaction
• The /bug command should open a bug submission interface
• Text rendering should handle all unicode/special characters gracefully

Actual Behavior

• CLI crashes with TypeError: Cannot read properties of undefined (reading 'codePointAt')
• Crash occurs in the string width measurement function (B3) at line 809:28790
• The error happens during text layout/wrapping calculations
• Unable to use the tool for any meaningful work due to frequent crashes
• Cannot even submit bugs through the built-in /bug command

Additional Context

Environment Details:

• OS: Linux (Ubuntu/Debian based on paths)
• Node.js versions tested: v22.18.0 and v20.19.4
• Installation path: ~/.nvm/versions/node/vXX/lib/node_modules/@anthropic-ai/claude-code/
• Frequency: Multiple crashes per day during regular usage

Full Stack Trace (Node v20.19.4):

ERROR  Cannot read properties of undefined (reading 'codePointAt')
 file:///home/user/.nvm/versions/node/v20.19.4/lib/node_modules/@anthropic-ai/claude-code/cli.js:809:28790
 - B3 (file:///home/user/.nvm/versions/node/v20.19.4/lib/node_modules/@anthropic-ai/claude-code/cli.js:809:28790)
 - SP2.stringIndexToDisplayWidth (file:///home/user/.nvm/versions/node/v20.19.4/lib/node_modules/@anthropic-ai/claude-code/cli.js:853:959)
 - SP2.getPositionFromOffset (file:///home/user/.nvm/versions/node/v20.19.4/lib/node_modules/@anthropic-ai/claude-code/cli.js:857:1040)
 - *5.getPosition (file:///home/user/.nvm/versions/node/v20.19.4/lib/node*modules/@anthropic-ai/claude-code/cli.js:853:208)
 - *5.render (file:///home/user/.nvm/versions/node/v20.19.4/lib/node*modules/@anthropic-ai/claude-code/cli.js:847:2255)
 - WT1 (file:///home/user/.nvm/versions/node/v20.19.4/lib/node_modules/@anthropic-ai/claude-code/cli.js:878:434)

Troubleshooting Already Attempted:

• ✗ Downgraded Node.js from v22 to v20
• ✗ Clean npm cache (npm cache clean --force)
• ✗ Complete reinstall of claude-code
• ✗ Fresh installation after removing all npm global packages

Analysis:
The issue appears to be in the text segmentation/measurement code where Intl.Segmenter or similar functionality produces undefined segments that the width calculation function cannot handle. The B3 function attempts to call codePointAt() on an undefined value during terminal text rendering.