Ark0N's PR #453 review: fit() was only ever called from the divider
drag, and the trailing-edge ResizeObserver callback in terminal-ui.js
(throttledResize) only ever measured Pane A's own container. Split at
a wide viewport, shrink the window (or toggle the Alt+B sidebar, or
drag the tab rail), and Pane A's cols changed while Pane B silently
kept its stale PTY size in both xterm and the real pane.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>