Additional Protection Mode for API Requests

What: Added support for an experimental additional protection mode that can be enabled via environment variable.

How to use:

# Enable additional protection for API requests
export CLAUDE_CODE_ADDITIONAL_PROTECTION=true
claude --prompt "your prompt here"

Details:

• When enabled, sets the x-anthropic-additional-protection header on API requests
• This is an experimental security feature that may provide enhanced request validation
• Only affects requests to Anthropic's API (not Bedrock or Vertex)
• Evidence: Added at bU() at line 203031-203032 in the API client initialization function