[BUG] Edit tool settings. json validator fails with "Unterminated string" when old string spans a line with backslash sequences

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?

When using the Edit tool to modify ~/.claude/settings.json, the post-edit validator throws Invalid JSON: JSON Parse error: Unterminated string if old_string spans a line containing a permission rule with backslash sequences. The file on disk is valid JSON - the validator accepted it when originally written. The error fires before any write occurs, so the file is never actually corrupted.

What Should Happen?

Expected behavior
Edit succeeds; Bash(jq *) is added to the allow list.

Error Messages/Logs

Invalid JSON: JSON Parse error: Unterminated string

Steps to Reproduce

1. Add "Bash(grep -E '\\.md$')" to permissions.allow in ~/claude/settings.json:

{
    "permissions": {
        "allow": [
            "Bash(grep -E '\\.md$')",
            "Bash(git *)"
        ]
    }
}

1. Use the Edit tool with an old_string that includes that line:

old_string: "Bash(grep -E '\\.md$')",\n    "Bash(git *)"
new_string: "Bash(grep -E '\\.md$')",\n    "Bash(git *)",\n    "Bash(jq *)"

1. Observe: Invalid JSON: JSON Parse error: Unterminated string

Workaround
Target a line that doesn't contain backslashes in old_string:

old_string: "Bash(git *)"
new_string: "Bash(git *)",\n    "Bash(jq *)"

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.128

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Warp

Additional Information

_No response_