Synchronized access to readQueue and isSendingReadAcks using the
existing concurrent DispatchQueue with barrier flags:
- sendReadReceipt(): wrap enqueue in barrier async
- processReadQueueIfNeeded(): extract item within barrier context
- scheduleNextReadAck(): wrap callback in barrier async
This fixes race conditions where concurrent calls could corrupt the
read queue or cause check-then-act bugs on isSendingReadAcks.
Also adds thread safety tests:
- concurrentReadReceiptEnqueue: 100 concurrent enqueue operations
- readQueueProcessingUnderLoad: concurrent enqueue during processing
- isPeerReachableThreadSafety: concurrent read access test
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
