sendMessage method
Send a message to the embedded session.
Implementation
Future<Message> sendMessage(String text) async {
if (!_isActive) {
throw StateError('Embedded session is not active');
}
final msg = Message.user(text);
_messageController.add(msg);
// Placeholder for actual API interaction.
final response = Message.assistant('');
_messageController.add(response);
return response;
}