[BUG] Claude Code does not respect agent model definition, uses wrong model.

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?

I've setup agents like this:

---
name: code-implementer
description: ---- redacted ----- 
model: opus
color: red
---

but when claude calls this model it uses sonnet:

code-implementer(job) resuming af473b5 Sonnet 4.5

This bug greatly reduces code quality, reasoning quality and other tasks quality. (planning, reviewing, etc.)

What Should Happen?

Claude should use opus for subagent because it's defined as opus.

Error Messages/Logs

no error. it just uses other models, without any reason.

Steps to Reproduce

1. Create an agent as opus.
2. Tell claude to delegate work to said agent.
3. Agent uses other model.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.?

Claude Code Version

2.1.7

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_