SessionStart hook additionalContext banner disappears on terminal resize

When a SessionStart hook outputs additionalContext via JSON on stdout, the banner text rendered in the terminal disappears when the terminal window is resized.

Repro

1. Configure a SessionStart hook that outputs additionalContext with multi-line text
2. Start a new Claude Code session — banner appears correctly
3. Resize the terminal window
4. Banner text disappears from visible terminal output

Expected

Banner text persists or reflows correctly after resize.

Actual

Banner clears visually. The context IS still injected into Claude's system message — purely a terminal rendering issue. Claude retains full access to the additionalContext data.

Environment

• Claude Code CLI (latest)
• Linux (Pop!_OS), GNOME Terminal / kitty
• Likely reproducible on macOS

Impact

Low / cosmetic. Context injection works fine — Claude retains the data.