When an edit grew the line count by a digit (999 -> 1000), the patched
editor dropped every measured wrapped-row height, so offscreen rows fell
back to one line and the viewport jumped thousands of pixels above the
caret. Keep heights above the edit, as other line-count changes already
do; rows the wider gutter rewraps are remeasured when rendered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>