On Windows, an alternate-screen TUI pane (Claude Code) could lose scroll-up
after being hidden (tab/worktree switch or app backgrounded) and shown again.
Root cause: on hidden->visible restore, applyMainBufferSnapshot
unconditionally wrote a destructive clear (\x1b[2J\x1b[3J\x1b[H) before
replaying the snapshot, wiping xterm's scrollback. The attach/reattach path
already guards this same clear behind !isAlternateScreen (pty-transport.ts);
the snapshot path did not.
Thread an alternateScreen flag from the backend headless serialization
through the pty:getMainBufferSnapshot IPC + preload types into
applyMainBufferSnapshot, and skip the destructive clear when restoring an
alternate-screen buffer. Add a regression test asserting the clear is NOT
emitted for an alt-screen restore (and the existing normal-buffer test still
asserts it IS).
Fixes#5723
brennanb2025
a0de430397