[BUG] Edit tool reports false success and shows simulated content without actually modifying files

Here's a summary you could use for the bug report:

Title: Edit tool reports false success and shows simulated content without actually modifying files

Description:
The Edit tool sometimes reports successful file modifications with convincing line-numbered output, but
doesn't actually write changes to the file.

Steps to reproduce:

1. Use Edit tool on an existing file (e.g., ~/.claude/CLAUDE.md)
2. Tool reports "The file has been updated" with line-numbered output
3. Verify actual file content - changes weren't applied

Expected behavior:

• Edit tool should actually modify the file when reporting success
• OR fail with clear error message if unable to make changes
• Should never show fake "results" that don't match actual file state

Actual behavior:

• Reports success with simulated line-numbered content
• Actual file remains unchanged
• Creates false confidence that the edit worked

Impact:

• Misleading feedback undermines trust in file operations
• Can cause confusion and wasted time
• Critical for coding assistant reliability

This would help the Claude Code team track and fix the issue.