- Run agent sessions under an isolated tmux server (its own systemd scope, with a
keepalive session) so they survive a castle-api restart and stay rediscoverable;
each WebSocket is a tmux attach client. Falls back to the in-memory pty backend
when tmux is absent or CASTLE_API_AGENT_BACKEND=memory.
- Refactor the session layer behind one Attachment interface (create/list/attach/
close), keeping resume-by-id, agent-native history, and continue modes.
- Fix the terminal not refilling when the dock is maximized (explicit refit signal
+ instant size transition so xterm measures the final box).
- On narrow screens, go full-bleed and strip chrome (header/border/padding) when
maximized.
