I don't know how they've specifically done it, either, but this is an area where Google has a ridiculous advantage over pure play AI shops. It's highly likely they have architected it for use cases like this from the outset, since the primary application of Gemini will be within Google's own products. They'll publish APIs, of course, and embed within Vertex AI on Google Cloud, but since the primary utility of Gemini will be to improve Search, Maps, Travel, Youtube, etc, I'd imagine they had a first class business requirement from the beginning along the lines of "must be easy to plug into existing Google data sources & products."