- Mount xterm as an absolute inset-0 fill so it always has an explicit box and
fit() measures the real size when the dock expands (was collapsing via the
flex/percentage height chain).
- Acquire the pty slave as the child's controlling terminal (setsid + TIOCSCTTY)
so the kernel delivers SIGWINCH on a browser resize. Previously the initial
size was read once but live resizes were dropped, so the pane stayed at its
startup size — content never grew with the window.
- 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.
