[BUG] PowerShell file write after non-terminating exception wiped source file (data loss)

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?

Claude used PowerShell to edit a C source file. A List<string>.AddRange() call failed with a type mismatch exception.
PowerShell treated this as a non-terminating error and continued executing. The subsequent
[System.IO.File]::WriteAllLines() call ran with an empty list, overwriting the file with 3 bytes and permanently
destroying its contents.
The project had no git history (Is a git repository: false). The file was only recoverable because the user happened
to have a manual backup.
Source file (SWG_ServerInterface.c, ~2731 lines) was reduced to 3 bytes. No warning was shown to the user before the destructive write occurred.

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Environment

• OS: Windows 11 Pro
• Shell: PowerShell 7+
• Git repository: No
• Claude Code version:2.1.173

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Severity

High — permanent data loss with no recovery path if user has no external backup. The failure mode is silent: the
script reports apparent success while the file is already destroyed.

What Should Happen?

Claude should either:

• Use the built-in Write/Edit tools for file modifications instead of PowerShell, or
• Validate that the output list is non-empty and matches expected line count before writing, or
• Treat any exception during file construction as fatal and abort before the write step

Error Messages/Logs

Steps to Reproduce

1. Open a project with no git repository
2. Claude attempts to edit a file using PowerShell with ReadAllLines → modify → WriteAllLines
3. An exception occurs mid-script (e.g. type mismatch on List<T>.AddRange)
4. PowerShell continues past the exception
5. WriteAllLines executes with an empty or partial result
6. File is overwritten and original content is lost

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.173

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

<img width="1110" height="678" alt="Image" src="https://github.com/user-attachments/assets/87e5e355-9c42-47c3-ae35-92a6d24272ea" />