review-concurrency-state

Review Apache Pinot diffs for concurrency, state management, visibility, atomic state transitions, lock changes, Helix IdealState updates, upsert metadata safety, consumer/stream ingestion races, and shared-observer correctness. Trigger keywords — synchronized, volatile, AtomicReference, ConcurrentHashMap, ReentrantLock, StampedLock, Helix, IdealState, ZkClient, version-checked write, upsert metadata, consumer coordinator, stream partition.