How to use a nested navigation graph for a login flow?

This tests your ability to modularize UI flows using Android's Navigation Component. A great answer outlines creating a separate `login_nav_graph.xml`, using `<include>` in the main graph to add it, and then navigating to the nested graph's ID to initiate the flow. The key benefits are encapsulation—the main graph is unaware of the login flow's internal screens—and reusability. The biggest red flag is navigating from outside directly to a screen *inside* the nested graph, which completely defeats the purpose of encapsulation.