[BUG] 2.1.283: no place in the UI shows a subagent's model (/tasks rows lost it, transcript view shows the parent's)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet (closest: #73572, #86489, #87605, all closed; #89133 covers parallel launches only)
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

On 2.1.283 there is no place in the terminal UI that shows which model a running subagent uses.

• The /tasks list rows show a status icon, the agent name, the description and the status, but no model or effort. The 2.1.243 changelog entry says "Added the model (and effort level) each subagent ran on to /tasks and the agent detail dialogs", and the 2.1.283 entry "Improved /tasks: rows show a status icon, the name and whole facts..." appears to have dropped it.
• The subagent transcript view ("Viewing @name · esc to return") shows the header "<parent model> with <effort> · <plan>" and the status line still reports the parent session's model. The JSON piped to a custom statusLine command while viewing a subagent carries only the session's model; there is no field for the viewed agent.

The model override itself works: the subagent's transcript JSONL records every API response with "model":"claude-sonnet-5", and the .meta.json next to it records "model":"sonnet". This is display only, but it is the same problem as #73572 / #86489 / #87605: users enforcing a cheaper model for subagents cannot verify it from the UI without stopping the agent and grepping transcripts.

What Should Happen?

/tasks rows and the subagent transcript view (header and/or status line payload) show the model and effort the subagent actually runs on, as 2.1.243 introduced. Ideally the statusLine stdin JSON gains a field for the viewed agent (name, model, effort) so custom status lines can render it.

Error Messages/Logs

(none; no error, the information is simply absent)

Steps to Reproduce

1. Start a session on a top-tier model (Fable 5.1 here).
2. Ask Claude to spawn a background subagent with an explicit override: Agent tool, subagent_type: "general-purpose", model: "sonnet", prompt "Reply with one line and stop".
3. Run /tasks: the row shows name, description and status only, no model.
4. Open the agent's transcript view: header and status line show the parent model (Fable 5.1).
5. Ground truth: grep -o '"model":"[^"]*"' ~/.claude/projects/<project>/<session>/subagents/agent-*.jsonl | sort | uniq -c shows only claude-sonnet-5.

Claude Model

Other: main session Fable 5.1, subagents Sonnet 5

Is this a regression?

Yes, this worked in a previous version (per the 2.1.243 changelog entry; not bisected between 2.1.243 and 2.1.282)

Last Working Version

Unknown, 2.1.243 or later per changelog

Claude Code Version

2.1.283 (Claude Code)

Platform

Anthropic API (Claude Max subscription)

Operating System

macOS 15.7.9

Terminal/Shell

Orca, zsh

Additional Information

Workaround that restores the information: the documented subagentStatusLine setting receives each task's resolved model and effort and can print them on the agent panel rows, which are visible in the transcript view too. It would be good if the default rows did this again.