extension/components/Terminal.tsx  →  WebSocket  →  backend/modules/pty-handler.js
         ↓                                                    ↓
    xterm.js render                                      tmux session

const term = new Terminal({ /* options */ });
const fitAddon = new FitAddon();
term.loadAddon(fitAddon);
term.open(containerRef.current);
fitAddon.fit();

// Debounce resize, sync xterm → PTY
fitAddon.fit();
ws.send(JSON.stringify({ type: 'resize', cols: term.cols, rows: term.rows }));

// Terminal → Backend
term.onData(data => ws.send(JSON.stringify({ type: 'input', data })));
// Backend → Terminal
ws.onmessage = (e) => term.write(JSON.parse(e.data).data);