fix: a closed terminal hangs its shell up instead of killing it, so the history is saved; idle shells end with their session, and on agent stop

cmd/agent/main.go

@@ -38,7 +38,11 @@ func main() {
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
 
-	if err := agent.New(cfg).Run(ctx); err != nil {
+	err := agent.New(cfg).Run(ctx)
+	// Stopping (an update, a restart): hang the terminals up, so their shells
+	// save their history instead of being killed.
+	agent.CloseTerminals()
+	if err != nil {
 		log.Fatalf("agent: %v", err)
 	}
 }