The names vary with the office suite (Copilot in Microsoft's, Gemini in Google's, Claude turning up inside more and more apps), but under every sparkle icon sits the machine you met in Module 1: a prediction engine with a context window.
What's changed is the plumbing. In a chat tab, you fill the window by pasting. Embedded in a document, the app fills it for you, with the page you have open. Which raises the question that matters: what exactly does it get to see?