Session/agent switcher renders at half screen size, ignoring terminal dimensions

When switching between sessions/agent tabs (e.g. via left/right arrow at an empty input line), the resulting view doesn't respect the terminal's actual screen size — it renders using only about half the screen, which looks broken/truncated.

Steps to reproduce:

1. Have multiple Claude Code sessions/jobs running.
2. With the input line empty, press left or right arrow to cycle to a different session.
3. Observe the switched-to session's UI only occupies roughly half the terminal width/height instead of the full window.

Environment:

• OS: Windows 11 Enterprise 10.0.26100
• Shell: PowerShell (primary)
• Terminal: Windows Terminal, version 1.24.11321.0

Resizing the terminal window after switching sometimes forces a redraw, suggesting the layout isn't recalculating against current terminal dimensions on switch.