Terminal scrollback jumps/flickers when output is being generated

Description

When scrolling up through terminal history while Claude is actively generating text output, the viewport jumps unpredictably - typically snapping to the very top of the scrollback buffer. This makes it impossible to read previous content during streaming.

Steps to reproduce

1. Ask Claude a question that produces a long response
2. While the response is being streamed, try to scroll up in the terminal to review earlier content
3. The viewport jumps unpredictably, usually snapping to the very top of the scrollback history

Expected behavior

Scroll position should be preserved while reviewing history, even during active text generation. The user should be able to freely scroll through previous output without interruption.

Actual behavior

The terminal viewport jumps erratically during output generation, typically snapping to the very top of the scrollback buffer, making it impossible to navigate history while Claude is streaming a response.