Swift Concurrency

{
  "skill_name": "swift-concurrency",
  "evals": [
    {
      "id": 0,
      "prompt": "Review this Swift 6.3/Xcode 26 concurrency build-settings plan: the team says Approachable Concurrency alone makes the whole module MainActor, strict concurrency should start at Targeted in Swift 6 mode, and CPU-heavy image decoding can stay on MainActor because nonisolated async functions now hop to a background executor. Correct the plan and give the smallest build-setting and code-level recommendations.",
      "expected_output": "A source-grounded settings review that separates Approachable Concurrency from Default Actor Isolation, states that Swift 6 mode uses complete strict concurrency with errors, and recommends @concurrent/nonisolated offloading for CPU-heavy work instead of blocking MainActor.",
      "files": [],
      "assertions": [
        "Separates Xcode's Approachable Concurrency setting from Default Actor Isolation and says MainActor-by-default requires Default Actor Isolation = MainActor.",
        "States that Swift 6 / 6.3 language mode uses complete strict concurrency and emits errors, while Targeted or Minimal are Swift 5 migration settings.",
        "Explains that nonisolated async functions stay on the caller's actor with nonisolated(nonsending) behavior unless @concurrent is used.",
        "Recommends offloading CPU-heavy work with @concurrent and a nonisolated context rather than leaving it on MainActor.",
        "Avoids broad architecture or SwiftUI state-management redesign beyond the concurrency settings and code-level fix."
      ]
    },
    {
      "id": 1,
      "prompt": "A SwiftUI app with Default Actor Isolation set to MainActor has errors around a @Observable StickerModel conforming to Exportable, a PhotoProcessor async method, and a legacy SDK imported with @preconcurrency. Give a diagnostic remediation plan that preserves behavior, avoids unchecked Sendable unless truly justified, and explains which fixes belong in swift-concurrency rather than architecture or navigation skills.",
      "expected_output": "A diagnostic remediation plan that uses @MainActor or isolated conformances for UI-bound state, explains nonisolated(nonsending) and @concurrent tradeoffs for PhotoProcessor work, treats @preconcurrency as temporary, and keeps architecture/navigation details as sibling handoffs.",
      "files": [],
      "assertions": [
        "Uses @MainActor isolation or an isolated conformance such as extension StickerModel: @MainActor Exportable for UI-bound protocol conformance errors.",
        "Explains when PhotoProcessor can stay on the caller's actor and when CPU-heavy work should move to @concurrent/nonisolated async code.",
        "Prefers value immutability, actor isolation, or synchronization over adding @unchecked Sendable by default.",
        "Treats @preconcurrency import as a temporary bridge for third-party modules with a documented removal plan.",
        "Routes module architecture, navigation implementation, and detailed SwiftUI state ownership to sibling skills instead of expanding this skill's scope."
      ]
    },
    {
      "id": 2,
      "prompt": "Review this synchronization plan for a Swift 6.3 app: use an actor for a synchronous metrics counter called from C callbacks, put NSLock inside an actor for cache mutation, hold a Mutex while awaiting a network fetch, and ban NSLock because it is not Sendable. Replace it with a modern concurrency-safe plan for iOS 16 through iOS 26.",
      "expected_output": "A synchronization review that chooses actors for async shared state, Mutex or OSAllocatedUnfairLock for synchronous state depending on deployment target, Atomic for simple counters or flags, avoids locks inside actors or across await, and corrects the NSLock Sendable claim without recommending it first.",
      "files": [],
      "assertions": [
        "Uses an actor for shared mutable state when asynchronous access and actor hops are acceptable.",
        "Uses Mutex for new c