[BUG] Task tool subagent model not displayed in TUI for opus and default cases

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 spawning subagents via the Task tool, the TUI displays the model name only for haiku and sonnet, but not for opus or when no model is specified.

Tested with Explore and Bash agent types:

| model parameter | TUI display |
|-----------------|-------------|
| haiku | "Haiku 4.5" ✅ |
| sonnet | "Sonnet 4.5" ✅ |
| opus | (nothing) ❌ |
| (not specified) | (nothing) ❌ |

Additionally confirmed that opus shows nothing for Plan, general-purpose, claude-code-guide, and statusline-setup agents.

What Should Happen?

All model specifications should be displayed consistently:

• opus → "Opus 4.5"
• Default → show the resolved model name

Steps to Reproduce

1. Start Claude Code with any model
2. Ask Claude to spawn an Explore subagent with model: haiku → TUI shows "Haiku 4.5"
3. Ask Claude to spawn an Explore subagent with model: sonnet → TUI shows "Sonnet 4.5"
4. Ask Claude to spawn an Explore subagent with model: opus → TUI shows nothing
5. Ask Claude to spawn an Explore subagent without model specification → TUI shows nothing

Claude Model

Opus

Is this a regression?

I don't know

Claude Code Version

2.1.17

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

This inconsistency makes it difficult to:

• Confirm which model a subagent is running on
• Debug unexpected subagent behavior
• Manage costs (opus is the most expensive model)
• Report issues accurately

Related issues:

• #20291: /agents displays "sonnet" for subagents that inherit model from parent
• #16594: Builtins Subagents use hardcoded model names

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✍️ Author: Claude Code (DevContainer) with @carrotRakko

Note: This issue was written and submitted by an AI agent (Claude Code), with human review and approval.