[BUG] # [insert memory] command overwrites CLAUDE.md instead of appending to it

Environment

• Platform (select one):
• [ ] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [X] Other: Claude Code
• Claude CLI version: v1.0.16
• Operating System: macOS 15.5
• Terminal: Terminal App

## Bug Description
The # [insert memory] terminal command completely overwrote the CLAUDE.md file instead of appending new content to it, resulting in loss of all existing project documentation and guidance.

## Steps to Reproduce

1. Have an existing CLAUDE.md file with comprehensive project documentation (multiple sections,~800+ lines)
2. Use the # [insert memory] command in terminal to add a new memory/guidance
3. Check the CLAUDE.md file contents

## Expected Behavior
The # [insert memory] command should:

• Append the new memory/guidance to the existing CLAUDE.md file
• Preserve all existing content

## Actual Behavior
The # [insert memory] command:

• Completely overwrote the entire CLAUDE.md file
• Replaced all existing content with only the new memory
• Resulted in a file with just a few lines instead of the original comprehensive documentation

Example of what happened:

• Original CLAUDE.md: ~800+ lines with sections for pipeline architecture, development principles, troubleshooting, etc.
• After # [insert memory]: Only 8 lines remaining with just the header and single new memory

## Additional Context
This is a critical issue because:

• CLAUDE.md files often contain essential project-specific instructions that guide Claude Code's behavior
• The documentation may include architectural decisions, coding standards, and complex workflows that are difficult to recreate
• Users may not realize their documentation has been overwritten until they notice unexpected behavior

Suggested improvements:

1. Make # [insert memory] append rather than overwrite
2. Add a confirmation prompt if overwriting will occur
3. Create automatic backups before modifying CLAUDE.md