[BUG] Background agent panel no longer visible in v2.1.122+

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?

## Description

In v2.1.121, when a background subagent is running, the bottom of the
terminal shows a real-time agent panel listing each agent with its
current action and token usage:

● main
○ test-author Writing app-shell.test.tsx file 1m 10s · ↓ 52.3k tokens

After upgrading to v2.1.126, this panel no longer appears. Only a
brief status text is shown inline:

• Churned for 3m 1s · 1 local agent still running

## Steps to reproduce

1. Launch any subagent (e.g. via the Agent tool)
2. While the subagent is running, observe the bottom of the terminal

## Expected behavior

Agent panel visible at the bottom, showing each agent's name, current
action, elapsed time, and token usage — as in v2.1.121.

## Actual behavior

Panel is absent. Only inline text N local agent still running shown.

## Environment

• Claude Code: 2.1.126
• OS: macOS 26.0.1 (arm64)
• Shell: zsh
• statusLine custom command configured in settings.json

## Notes

This change is not mentioned in the changelog. It may be an
unintentional regression. The subagentStatusLine setting is
documented but adding it does not restore the panel visibility.

What Should Happen?

When a background subagent is running, a real-time agent panel should appear at the
bottom of the terminal showing each agent's name, current action, elapsed time,
and token usage — as it did in v2.1.121:

● main
○ test-author Writing app-shell.test.tsx file 1m 10s · ↓ 52.3k tokens

Error Messages/Logs

Steps to Reproduce

1. Configure a statusLine custom command in settings.json
2. Launch any subagent via the Agent tool
3. Observe the bottom of the terminal while the subagent is running

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

v2.1.121

Claude Code Version

v2.1.126

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_