#31922 made embedded terminals automatically grow to fit the content. We
since found some issues with large output which this PR addresses by:
- Only shaping / laying out lines that are visible in the viewport
(based on `window.content_mask`)
- Falling back to embedded scrolling after 1K lines. The perf fix above
actually makes it possible to handle a lot of lines, but:
- Alacrity uses a `u16` for rows internally, so we needed a limit to
prevent overflow.
- Scrolling through thousands of lines to get to the other side of a
terminal tool call isn't great UX, so we might as well set the limit
low.
- We can consider raising the limit when we make card headers sticky.
Release Notes:
- Agent: Improve handling of large terminal output
b103d7621b