Update it as the walk moves

Starting the activity

Activity<WalkActivityAttributes>.request(attributes:content:pushType:) starts a new Live Activity: pass the static WalkActivityAttributes, an ActivityContent wrapping the initial ContentState, and a pushType (.token if you want to push updates remotely, nil if updates only ever come from the app while it's foreground/background-active). It returns the running Activity — hang onto it, you'll need it to push updates.