[BUG] Interactive mode hangs when prompt follows --mcp-config (argument order)

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 using --mcp-config in interactive mode (no -p), placing the prompt after the flag causes claude to hang indefinitely with no output. Placing the prompt before the flags works fine.

This seems to contradict the documented usage: claude [options] [command] [prompt]

I saw some older closed issues about --mcp-config argument parsing (#5593, #16122) but those were about error messages, not hangs. And they were closed for inactivity rather than being fixed. This might be related or might be something different - not totally sure.

What Should Happen?

Based on the help text, this should work:

claude --mcp-config config.json "my prompt"

Steps to Reproduce

# This HANGS indefinitely (documented order):
claude --strict-mcp-config --mcp-config /path/to/config.json "say hello"

# This WORKS (undocumented order):
claude "say hello" --strict-mcp-config --mcp-config /path/to/config.json

The MCP config file is valid JSON with mcpServers defined. The hang happens before any UI appears - just a blank terminal.

Using -p (print mode) with the documented order works fine, so this seems specific to interactive mode.

Error Messages/Logs

No error messages - it just hangs with no output.

Claude Model

Opus

Is this a regression?

I don't know

Claude Code Version

2.1.29

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Workaround from the older issues (-- separator) might work here too, haven't tested it. For now I'm just putting the prompt first which does the job.