swift-concurrency-expert

# Swift Concurrency Expert _Attribution: copied from @Dimillian’s `Dimillian/Skills` (2025-12-31)._ ## Overview Review and fix Swift Concurrency issues in Swift 6.2+ codebases by applying actor isolation, Sendable safety, and modern concurrency patterns with minimal behavior changes. ## Workflow ### 1. Triage the issue - Capture the exact compiler diagnostics and the offending symbol(s). - Identify the current actor context (`@MainActor`, `actor`, `nonisolated`) and whether a default actor isolation mode is enabled. - Confirm whether the code is UI-bound or intended to run off the main actor. ### 2. Apply the smallest safe fix Prefer edits that preserve existing behavior while satisfying data-race safety. Common fixes: - **UI-bound types**: annotate the type or relevant members with `@MainActor`. - **Protocol conformance on main actor types**: make the conformance isolated (e.g., `extension Foo: @MainActor SomeProtocol`). - **Global/static state**: protect with `@MainActor` or move into an actor. - **Background work**: move expensive work into a `@concurrent` async function on a `nonisolated` type or use an `actor` to guard mutable state. - **Sendable errors**: prefer immutable/value types; add `Sendable` conformance only when correct; avoid `@unchecked Sendable` unless you can prove thread safety. ## Reference material - See `references/swift-6-2-concurrency.md` for Swift 6.2 changes, patterns, and examples. - See `references/swiftui-concurrency-tour-wwdc.md` for SwiftUI-specific concurrency guidance.