[BUG] Built-in subagents (Explore, claude-code-guide, statusline-setup) use hardcoded model names, ignoring parent model

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

Built-in subagents have hardcoded model defaults instead of inheriting from the parent:

| Agent Type | Actual Model | Expected |
|------------|-------------|----------|
| Explore | claude-haiku-4-5-20251001 | Inherit from parent |
| claude-code-guide | claude-haiku-4-5-20251001 | Inherit from parent |
| statusline-setup | claude-sonnet-4-6 | Inherit from parent |
| Plan | claude-opus-4-6 | ✅ Inherits correctly |
| general-purpose | claude-opus-4-6 | ✅ Inherits correctly |

The Task tool system prompt says "If not specified, inherits from parent" — this is incorrect for the three hardcoded agents.

What Should Happen?

All built-in agents should inherit the parent model by default, consistent with the documented behavior. Users paying for Opus get Haiku subagents without knowing it.

Steps to Reproduce

1. Start Claude Code with Opus
2. Spawn an Explore agent: Task(subagent_type="Explore", prompt="What model are you?")
3. The agent reports claude-haiku-4-5-20251001 instead of the parent's model

Claude Model

Opus

Is this a regression?

No, this never worked

Claude Code Version

2.1.70

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

iTerm2

Additional Information

Continuation of #16594, which was closed as inactive.

Additional finding: the Task tool's model parameter has been removed.

In v2.1.17 (#16594, #20419), the Task tool accepted a model parameter (haiku, sonnet, opus) that could override built-in agent defaults. As of v2.1.70, this parameter no longer exists in the tool schema — there is no way for the parent model to override a subagent's hardcoded model.

This means:

• Explore and claude-code-guide are unconditionally locked to Haiku
• statusline-setup is unconditionally locked to Sonnet
• There is no workaround available to users

✍️ Author: Claude Code with @carrotRakko (AI-written, human-approved)