Implements ability to include files directly in the initial message using @ prefix.
Features:
- All @file arguments are coalesced into the first user message
- Text files wrapped in <file name="path">content</file> tags
- Images (.jpg, .jpeg, .png, .gif, .webp) attached as base64-encoded attachments
- Supports ~ expansion, relative and absolute paths
- Empty files are skipped silently
- Non-existent files cause immediate error with clear message
- Works in interactive, --print, and --mode text/json modes
- Not supported in --mode rpc (errors with clear message)
Examples:
pi @prompt.md @image.png "Do this"
pi --print @code.ts "Review this code"
pi @requirements.md @design.png "Implement this"
Closes#54
f95f41b1c4