React context re-renders entire tree - how to optimize with useMemo and selectors?

The selector pattern you want is use-context-selector or the newer React.use() with a memoized slice. But honestly, for auth state specifically, the cleanest approach is to split your context into AuthStateContext (user object, rarely changes) and AuthTokenContext (token, refreshes often). Components that only need the user subscribe to AuthStateContext and never re-render on token refresh. Provider nesting is fine - wrap them in a single AuthProvider component that encapsulates both.