Pane B's SplitTerminalPane.connect() only opened a WebSocket and waited for
live output — ws-routes.ts's terminal socket sends nothing on connect, only
future 'terminal' events — so it stayed blank until the target session
happened to produce new output. It looked intermittent rather than
always-broken because a resize sent by _sendResize() often nudges the
session's real tmux window to a new size, and tmux repaints its current
screen on resize; that incidental repaint was what usually populated the
pane. When Pane B's computed dimensions already matched the session's
last-known size, Session.resize() skipped the resize as a no-op and the
pane stayed empty. Fetch the existing scrollback (?full=1) before opening
the socket, same as the primary pane does.
Pane A never told its own session's PTY/tmux about a size change at all,
relying purely on the passive 300ms-debounced ResizeObserver in
terminal-ui.js. openSplitPane() now force-resizes Pane A immediately on
entering split (mirroring closeSplitPane()'s existing symmetric call), and
the divider-drag handler force-resizes it once at drag end (matching the
codebase's established trailing-edge debounce convention rather than
flooding a resize per mousemove).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
