Navigation params typing

The param list type is the single source of truth for every route contract in the app. Once RootStackParamList exists, three things become compile errors instead of runtime crashes: navigating to a screen that doesn't exist, forgetting a required param (navigate('Profile') without userId), and reading a param that was never declared. On a team, this type is the navigation documentation — a new screen isn't done until it's in the param list.

The conventions worth naming: undefined for param-less screens isn't a placeholder — it's what makes navigate('Home') legal with no second argument while navigate('Profile', { userId }) requires one. NativeStackScreenProps<ParamList, 'Profile'> derives both route.params and a navigation prop that knows every valid destination. Passing the generic to createNativeStackNavigator<RootStackParamList>() types the navigator itself, and declaring the list on React Navigation's RootParamList global interface makes bare useNavigation() typed everywhere without per-call generics.

Red flag: typing useNavigation<any> or scattering local type Params = ... next to each screen. Duplicated route contracts drift, and any silently converts every navigation typo into a runtime crash — the exact bug class this type exists to delete.

Say it: "One central param list makes every route and param a compile-time contract — undefined means no params required, and the screens derive their props from it instead of redeclaring them."