[BUG] --agent option does not work with -p

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?

claude --agent Plan -p "what agent are you?" does not successfully engage the Plan agent, but launching the CLI with claude --agent Plan does succeed.

What Should Happen?

claude --agent Plan -p "what agent are you?" should use the Plan agent.

Error Messages/Logs

Steps to Reproduce

❯ claude -p "what agent are you?"        
I am **Claude Code**, an interactive CLI tool built on Anthropic's Claude Agent SDK. I'm powered by the **Claude Opus 4.5** model (model ID: `claude-opus-4-5-20251101`).
[...]

❯ claude --agent Plan -p "what agent are you?"
I am **Claude Code**, an interactive CLI tool built on Anthropic's Claude Agent SDK. I'm powered by the **Claude Opus 4.5** model (model ID: `claude-opus-4-5-20251101`).
[...]

❯ claude --agent Plan                         

╭─── Claude Code v2.0.76 ────────────────────────────────────────────────────────────────────────────────────────────────╮
│                                                    │ Tips for getting started                                          │
│                 Welcome back Tyler!                │ Run /init to create a CLAUDE.md file with instructions for Claude │
│                                                    │ ───────────────────────────────────────────────────────────────── │
│                    * ▗ ▗   ▖ ▖ *                   │ Recent activity                                                   │
│                   *             *                  │ No recent activity                                                │
│                    *   ▘▘ ▝▝   *                   │                                                                   │
│                                                    │                                                                   │
│ Opus 4.5 · API Usage Billing · My Company │                                                                   │
│                   Plan · ~/test                   │                                                                   │
╰────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

  Your bash commands will be sandboxed. Disable with /sandbox.

  Welcome to Opus 4.5

> what agent are you? 

⏺ I am a software architect and planning specialist for Claude Code. My role is specifically focused on:

  [...]

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.76

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_