Concurrency Review

It reviews thread safety issues, race conditions, and deadlocks across synchronized blocks, CompletableFuture chains, and Spring's @Async annotations. The skill covers modern patterns too: Virtual Threads, ScopedValue over ThreadLocal, and Java 25's structured concurrency. It's especially useful for catching Spring @Async gotchas like calling async methods from the same class or forgetting to configure a proper thread pool. Run it when you're touching anything with shared state or multiple threads. Concurrency bugs are timing dependent and hard to reproduce, so having an extra set of eyes before merge saves you from debugging race conditions at 2am.