React 18 Legacy Context Migration

Legacy context (contextTypes, childContextTypes, getChildContext) was deprecated in React 16.3 and warns in React 18.3.1. It is removed in React 19.

This Is Always a Cross-File Migration

Unlike most other migrations that touch one file at a time, context migration requires coordinating:

1. Create the context object (usually a new file)
2. Update the provider component
3. Update every consumer component

Missing any consumer leaves the app broken - it will read from the wrong context or get undefined.

Migration Steps (Always Follow This Order)