[BUG] Bug: "Bad substitution" crash on `!` character in code/responses (Windows)

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?

Bug: "Bad substitution" crash on ! character in code/responses

Environment

• Claude Code version: 2.1.7
• VS Code version: 2.1.7
• OS: Windows 11
• Shell: Git Bash (C:\Program Files\Git\bin\bash.exe)

Description

Claude Code crashes with "Bad substitution" error whenever it encounters a ! character in project code or AI-generated responses. This appears to be caused by bash history expansion (!command) being incorrectly triggered by the internal parser.

Steps to Reproduce

1. Open any project containing JavaScript/TypeScript code with ! operators (e.g., !isEnabled, !card.enabled, !==)
2. Start a conversation in Claude Code
3. Claude Code crashes when processing the code or generating a response containing !

Error Log

2026-01-15T09:18:38.582Z [ERROR] "Error: Error: Bad substitution: card.enabled
    at F (B:/~BUN/root/claude.exe:76:2562)
    at <anonymous> (B:/~BUN/root/claude.exe:76:3213)
    at map (native:1:11)
    at QRf (B:/~BUN/root/claude.exe:76:2302)
    at <anonymous> (B:/~BUN/root/claude.exe:76:3367)
    at dW (B:/~BUN/root/claude.exe:76:3817)
    at jRH (B:/~BUN/root/claude.exe:4314:1755)
    at u4 (B:/~BUN/root/claude.exe:4320:195)
    at i7$ (B:/~BUN/root/claude.exe:4320:1714)
    at isReadOnly (B:/~BUN/root/claude.exe:2894:1961)"

Also crashes on:

[ERROR] "Error: Error: Bad substitution: !isEnabled

Expected Behavior

Claude Code should handle ! characters in code without crashing. The bash history expansion should be disabled or properly escaped in the internal parser.

Additional Context

• The crash occurs even with a clean settings.local.json (no problematic allowed commands)
• Disabling bash history expansion (set +H in .bashrc) does not fix the issue
• The bug makes Claude Code unusable for any project containing negation operators or !== comparisons

Workaround

Currently no workaround available. Downgrading to an earlier version may help.

What Should Happen?

Claude Code should handle ! characters in code without crashing. The bash history expansion should be disabled or properly escaped in the internal parser.
Additional Context

The crash occurs even with a clean settings.local.json (no problematic allowed commands)
Disabling bash history expansion (set +H in .bashrc) does not fix the issue
The bug makes Claude Code unusable for any project containing negation operators or !== comparisons

Error Messages/Logs

2026-01-15T09:18:38.582Z [ERROR] "Error: Error: Bad substitution: card.enabled
    at F (B:/~BUN/root/claude.exe:76:2562)
    at <anonymous> (B:/~BUN/root/claude.exe:76:3213)
    at map (native:1:11)
    at QRf (B:/~BUN/root/claude.exe:76:2302)
    at <anonymous> (B:/~BUN/root/claude.exe:76:3367)
    at dW (B:/~BUN/root/claude.exe:76:3817)
    at jRH (B:/~BUN/root/claude.exe:4314:1755)
    at u4 (B:/~BUN/root/claude.exe:4320:195)
    at i7$ (B:/~BUN/root/claude.exe:4320:1714)
    at isReadOnly (B:/~BUN/root/claude.exe:2894:1961)"

Steps to Reproduce

Open any project containing JavaScript/TypeScript code with ! operators (e.g., !isEnabled, !card.enabled, !==)
Start a conversation in Claude Code
Claude Code crashes when processing the code or generating a response containing !

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.6

Claude Code Version

2.1.7

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_