Closed subagent remains visible in Subagents panel

Summary

A subagent that was closed through Codex still remained visible in the Subagents panel.

Observed behavior

After requesting the subagent be closed, the UI still showed the subagent entry:

• Name: Kuhn
• Role: explorer
• Panel: Subagents

A follow-up close call returned a pending_init-style previous status, but the UI still appeared to show the subagent as present.

Expected behavior

When a subagent is closed, the Subagents panel should either remove it, mark it clearly as closed, or refresh to show the correct state.

Why this matters

Users may think a subagent is still running or consuming resources after it has been closed. This is especially confusing when using subagents for verification or sandbox testing.

Repro outline

1. Spawn a subagent from a Codex thread.
2. Wait for or receive its completed result.
3. Close the subagent.
4. Check the Subagents panel.
5. The closed subagent may still appear as active/listed.