Car UIs have strict distraction guidelines. This article turns that observation into a small implementation model you can test, measure, and keep boring when the app grows. The problem in one sentence What belongs on the car screen and what does not. The useful question is not whether the API or pattern looks elegant in isolation. It is where state lives, which boundary owns failure, and how a user recovers when the happy path disappears. A practical model Glanceable actions only; no text entry while driving. Start with one explicit owner for the behavior. Keep widgets responsible for rendering and user intent; keep IO, persistence, permissions, and retries behind a small interface. That gives you a seam for a fake in tests and a place to record the facts that matter in production. For a Flutter app, the boundary usually looks like this: The widget emits an intent such as load, submit, refresh, or retry. A controller or use case validates the intent and calls the boundary. T...