Output renders line-by-line from bottom, causing slow scroll and poor readability for long responses

Describe the bug

New output tokens render one line at a time, appearing from behind the input box area and scrolling upward. Instead of efficiently displaying large blocks of output, the terminal slowly streams each line from the bottom of the viewport, pushing content upward incrementally.

This creates several problems:

1. Painfully slow for long output — A response that could be read in seconds takes minutes to fully render because each line animates into view sequentially
2. Visual distraction — The constant upward scrolling motion makes it difficult to read content as it arrives
3. No way to skip ahead — You're forced to watch the scroll animation even when the content has already been generated
4. Looks unpolished — The line-by-line reveal from behind the input box feels like an unintended side effect rather than a deliberate design choice

Expected behavior

Output should render as fast as tokens arrive without an artificial line-by-line scroll animation. For large outputs, content should appear in chunks or snap into place — similar to how a normal terminal works or how previous versions of Claude Code handled it.

Environment

• OS: macOS (Darwin 25.3.0)