Swift Concurrency Review, fix, and write concurrent Swift code targeting Swift 6.3+. Gate Swift 6.4 / Xcode 27 beta cleanup APIs behind explicit toolchain and availability checks. Apply actor isolation, Sendable safety, and modern concurrency patterns with minimal behavior changes. Contents - Triage Workflow - Swift 6.2 Language Changes - Actor Isolation Rules - Sendable Rules - Structured Concurrency Patterns - Task Cancellation - Actor Reentrancy - AsyncSequence and AsyncStream - - Synchronization Primitives - Common Mistakes - Review Checklist - References Triage Workflow When diagnosing a…