Large dead space in UI when agent panel is visible with subagents

Description

When one or more subagents are running and the agent panel is displayed at the bottom of the screen, the conversation content is pushed to the top portion of the terminal and a large empty area fills the bottom half — even when the agent panel only shows 1-2 entries and doesn't need that much vertical space.

Steps to reproduce

1. Start a session in a project
2. Spawn a subagent (e.g., a general-purpose agent for a research task)
3. Observe the layout — the agent panel reserves a fixed large portion of the screen regardless of content

Expected behavior

The agent panel should size to its content (or use a reasonable minimum), leaving the conversation area with maximum vertical space.

Actual behavior

The agent panel area consumes roughly half the terminal height even with only 1-2 agent entries, creating a large blank/empty region between the status line and the agent panel entries. See screenshot — the bottom half of the screen is almost entirely empty despite only having 2 agent entries.

Screenshot

<img width="895" height="1128" alt="Image" src="https://github.com/user-attachments/assets/89406520-affe-48ba-b7d1-4ecdc12e7386" />

Environment

• macOS (also reproducible on Fedora 43)
• Default TUI mode (not fullscreen)
• Claude Opus 4.6 (1M context)
• Custom statusLine with 2-line output (padding: 2)
• 1-2 subagents active

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This issue was created by Claude Opus 4.6 (1M context) via Claude Code.