Sessions

A session is one program’s terminal: the program (your shell, Claude Code, a dev server), its pseudo-terminal (ConPTY on Windows), and a full copy of the terminal’s state in libghostty: the screen, the scrollback, the modes, even half-received escape sequences.

Each session is its own process. A small background server starts sessions and finds them again; windows, alto attach and other computers are clients that attach to them.

Why it outlives the window

Because the window doesn’t own anything. Quit the app, update it, or let it crash, and every session carries on. Open it again and the window remembers its tabs, their splits, which pane had focus, each pane’s profile and which tab was in front, and attaches to them all again.

A crash in one session takes down that session, not the others. The server holds nothing it can’t rebuild from small records on disk, so it can restart or be replaced without touching a running session.

The background service

The server starts at login, so sessions are there before you open the app: a LaunchAgent on macOS, a systemd user unit on Linux, a Run key on Windows. The app sets this up; without the app:

alto service install   # start the server at login
alto service status
alto server status     # is it running now

Several clients, one session

Any client can show a session and any can type. The session’s size follows whoever typed last; the others draw it at that size with a note, Sized for another window, and Resize to fit takes it back. alto attach asks whether to fit, resize or just watch, or takes --fit or --watch.

Ended sessions

A session that was killed or stopped (the computer restarting), rather than its program exiting, saved its screen as it went. Its pane shows that last screen, scrollback included, and takes no typing; scrolling, selecting, copying and finding still work.

Its note says This session has ended, when its screen was saved, and offers one button: Resume Claude, Run vim again, New shell. Enter does the same. It starts the command again in the folder it was last in, in the same place in the tab; an agent picks up its own conversation if its hooks are installed.

Closing an ended tab forgets its save. A program that exits on its own leaves nothing behind, and its pane closes.

alto capture ID prints an ended session’s screen and scrollback, as it last saved them.