Extra blank lines rendered around SessionStart hook output and first response

Description

Extra blank lines appear in the terminal UI at session start:

1. A blank line after the SessionStart hook output (before the first user prompt)
2. A blank line before the assistant's first response

This happens even when hooks produce no stdout output — the spacing seems to come from the CLI's rendering logic around hook notification banners.

Steps to reproduce

1. Have a plugin with a SessionStart hook registered (e.g., aurora-core's version-check.sh)
2. Start a new Claude Code session
3. Type a simple message like echo hi
4. Observe blank lines before the assistant response and between the hook banner and the prompt

Expected behavior

No extra blank lines — the hook banner, user prompt, and assistant response should flow without unnecessary vertical whitespace.

Actual behavior

An empty line appears after the SessionStart:startup says: banner, and another empty line appears before the assistant's response to the first user message. See attached screenshot context: the hook output section and "Hi!" response have extra vertical gaps.

Environment

• Claude Code CLI (terminal)
• Linux (Ubuntu)
• Multiple plugins with SessionStart hooks (aurora-core, braintrust tracing)