[Bug] Background subagents sometimes missing from terminal bottom status area

Bug Description
Sometimes when multiple subagents are running in the background, the main session
does not show them in the status area at the bottom of the terminal.

The tasks themselves run fine — completion notifications still arrive and their
outputs are written correctly. This appears to be a display-only issue.

Steps to Reproduce

1. In a single assistant turn, launch several background agents at once

(e.g., 3 Agent tool calls in one message).

1. Watch the status area at the bottom of the terminal while they run.

Expected Behavior
All running background agents are listed at the bottom of the terminal.

Actual Behavior
Sometimes none (or only some) of them are shown.

Environment

• Platform: macOS (darwin)
• Terminal: Apple_Terminal
• Claude Code version: 2.1.220
• Feedback ID: 97b6b226-fae5-4dd5-977a-a7b7fb73d033