[BUG] @ File Reference Feature Not Working on macOS

Environment

• Platform (select one):
• [x] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.21 (Claude Code)
• Operating System: macOS 15.5
• Terminal: Terminal App (also tested in VS Code and VS Code Insiders)

## Bug Description
The @ symbol file reference feature does not work in any environment - it doesn't show the file picker/autocomplete list
when typing @ in chat messages.

## Steps to Reproduce

1. Open Claude Code in terminal, VS Code, or VS Code Insiders
2. Start typing a message to Claude
3. Type the @ symbol
4. Wait for file picker/autocomplete to appear

## Expected Behavior
After typing @, a file picker or autocomplete list should appear showing available files in the workspace/directory that
can be referenced.

## Actual Behavior
Nothing happens when typing @. No file picker, no autocomplete, no visual indication that file referencing is available.

## Additional Context

• Tested across multiple environments: Terminal, VS Code, VS Code Insiders
• Performed complete uninstall/reinstall of Claude Code extension
• Manually removed all Claude Code related files from macOS
• Issue persists across all clean installations
• Have active workspace/folder open in VS Code when testing