React18 Batching Patterns

If you're migrating a class component codebase to React 18, this is your batching regression field guide. React 18 now batches setState calls inside setTimeout, promises, and async/await where React 17 didn't, which silently breaks code that reads this.state after an await to make decisions. The skill gives you a three category diagnostic tree and shows exactly when to use flushSync versus when to refactor. The real value is the flushSync discipline, it stops you from papering over batching issues with synchronous renders everywhere, which would kill the performance gains you upgraded for. Includes a comparison table and concrete before/after patterns for each scenario.