[BUG] Slash command with additional arguments not recognized

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?

Slash commands that include additional arguments are not being recognized
as commands. Only the bare command (e.g. /mcp) works — as soon as
arguments are appended (e.g. /mcp something), it is treated as plain text.

Actual Behavior

/mcp something is submitted as a plain text message instead of being
parsed as a command with arguments.

Environment

• Claude Code version: 2.1.146 (Claude Code)
• OS: Ubuntu 22.04.5

What Should Happen?

/mcp something should execute the /mcp command and pass something
as an argument.

Error Messages/Logs

Steps to Reproduce

1. Have a slash command defined (e.g. /mcp)
2. Type /mcp → works correctly ✓
3. Type /mcp something (with arguments) → not recognized ✗

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.146 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Cursor

Additional Information

_No response_