Background session UI: 'describe a task for a new session' input stuck in conversation view with large blank space

Bug Description

When using Claude Code in background session mode, the UI layout breaks:

• Large blank/black area occupies the top portion of the screen
• The ❯ describe a task for a new session input line is stuck in the middle of the view
• Conversation messages are pushed below that input line instead of filling the main area
• Sessions list UI and conversation view appear overlapped/mixed

Expected Behavior

The conversation should fill the main area normally with input at the bottom — same as a regular interactive session.

Actual Behavior

The sessions list UI (describe a task for a new session input) is rendered inside/over the conversation view. Large blank space at top, sessions input in middle, conversation messages crammed below.

Steps to Reproduce

1. Start or receive a background session in Claude Code desktop app
2. View the session while it is active
3. Observe: large blank space at top, describe a task for a new session input in middle, conversation messages below

Environment

• Platform: macOS (Darwin 24.6.0)
• Claude Code desktop app