[BUG] @ autocomplete menu requires additional character - does not trigger on @ alone (incorrectly closed as duplicate)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When typing @ in the Claude Code input field, the autocomplete menu does NOT appear immediately. The dropdown only shows up after typing at least one character following the @.

• Current behavior: @ → nothing happens → @f → dropdown appears
• Expected behavior: @ → dropdown appears immediately

This is a regression from previous behavior where the dropdown would appear instantly upon pressing @, allowing users to browse all available files and MCP servers before typing.

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⚠️ Important: Previous Reports Incorrectly Closed

This issue was previously reported in #13883 but was incorrectly closed as a duplicate of #13807. These are completely different bugs:

| Issue | Problem |
|-------------------|----------------------------------------------------------------------------------|
| #13883 (this bug) | @ autocomplete menu doesn't trigger until you type additional characters after @ |
| #13807 | Text typed before @ is cleared after selecting from the dropdown |

#13807 was about input text preservation after using the dropdown. #13883 (and this report) is about the dropdown not appearing at all when only @ is typed.

Please do not close this as a duplicate of #13807 - they address fundamentally different behaviors.

What Should Happen?

When pressing @, a dropdown/autocomplete menu should appear IMMEDIATELY (without needing to type additional characters), showing:

1. Available files in the current project that can be mentioned
2. Configured MCP servers that can be enabled/disabled

Previously, pressing @ alone would trigger the menu, allowing users to browse options before narrowing down with typed characters.

Error Messages/Logs

No error messages displayed. The @ character is typed but the expected autocomplete/mention popup simply does not appear.

Steps to Reproduce

1. Open PowerShell on Windows 11
2. Navigate to any directory (e.g., cd C:\Users\user)
3. Run claude to start Claude Code CLI
4. In the input field, type ONLY the @ character (don't type anything after)
5. Expected: A dropdown menu should appear immediately with files and MCP options
6. Actual: Nothing happens - the dropdown does NOT appear
7. Now type one more character (e.g., @f)
8. Actual: NOW the dropdown appears and starts filtering

The issue is that @ alone no longer triggers the menu - you must type @<character> for it to show.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.71

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Technical hypothesis: This is likely a debounce/trigger threshold change in the autocomplete logic. Previously the trigger was "on @ keypress", now it seems to be "on @ + minimum 1 character". This could be:

• An intentional change that broke UX expectations
• A regression in input event handling
• A race condition where the menu checks for content length before rendering

Duplicate closure chain (for maintainers):

• My original report → closed as duplicate of #13883 ✅ (correct)
• #13883 → closed as duplicate of #13807 ❌ (incorrect - different bugs)

Both the original reports in #13883 and this submission describe the same autocomplete trigger issue, which is unrelated to the text-clearing bug in #13807. Please reopen #13883 or track this separately.