In Home Assistant a voice assistant is a combination of a speech-to-text, conversation and text-to-speech engines. A user can create as many combinations as they want. For a conversation agent, it's text command in, text response out. We already have the option to use OpenAI GPT 3.5, so it's possible in the future to hook it up to a large language model and allow it to control your house.

Fun fact: we supported Almond (later Genie), the IoT AI from Stanford which they released a couple of years ago. It would convert natural language into their ThingTalk language, which could do things like you mention. It was not popular at all and Stanford ended up shutting it down.