fix(concurrency): clear 4 Swift 6 warnings under default MainActor isolation

- ModelStore/FileVault: drop nonisolated(unsafe) on shared, mark all instance
  methods nonisolated (they only read filesystem); ModelKind enum also nonisolated
- AIRuntime ↔ ModelStore cross-actor call resolved by the above
- LLMSession: replace deprecated Device.setDefault(device:) with task-scoped
  Device.withDefaultDevice(.cpu, body:); wrap both load and generate so the
  TaskLocal propagates through ModelContainer.perform

康康/AI/LLMSession.swift

@@ -12,18 +12,27 @@ actor LLMSession {
         self.container = container
     }
 
+    /// 在 simulator 把默认设备强切为 CPU(MLX 的 Metal backend 在部分 Sim 路径会 abort)。
+    /// 真机走 body 默认设备(GPU/ANE)。
+    /// 用 task-scoped `withDefaultDevice`,TaskLocal 会传递到 child Task / actor 调用。
+    private static func withDeviceOverride<R>(
+        _ body: () async throws -> R
+    ) async rethrows -> R {
+        #if targetEnvironment(simulator)
+        return try await Device.withDefaultDevice(.cpu, body)
+        #else
+        return try await body()
+        #endif
+    }
+
     /// 从本地目录加载模型(包含 config.json + weights + tokenizer)。
     static func load(folderURL: URL) async throws -> LLMSession {
-        #if targetEnvironment(simulator)
-        // MLX 的 iOS Simulator GPU stream 初始化会在部分 Metal backend 路径中 abort。
-        // 模拟器只用于功能调试,强制走 CPU;真机仍保留默认 GPU/ANE 相关路径。
-        Device.setDefault(device: .cpu)
-        #endif
-
         let configuration = ModelConfiguration(directory: folderURL)
-        let container = try await LLMModelFactory.shared.loadContainer(
+        let container = try await withDeviceOverride {
+            try await LLMModelFactory.shared.loadContainer(
                 configuration: configuration
             )
+        }
         return LLMSession(container: container)
     }
 
@@ -35,6 +44,7 @@ actor LLMSession {
         AsyncThrowingStream { continuation in
             let task = Task {
                 do {
+                    try await Self.withDeviceOverride {
                         let parameters = GenerateParameters(
                             maxTokens: maxTokens,
                             temperature: Float(0.6),
@@ -76,6 +86,7 @@ actor LLMSession {
                             // 文字,GPU 是否完全空闲不影响数据正确性。去掉此调用同时省
                             // 一份 transitive import MLX 的依赖,简化 SPM 链接。
                         }
+                    }
                     continuation.finish()
                 } catch {
                     continuation.finish(throwing: error)

康康/AI/ModelStore.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-enum ModelKind: String, CaseIterable {
+nonisolated enum ModelKind: String, CaseIterable {
     /// 与 HuggingFace mlx-community 仓库名一一对应,也是沙盒 Models/ 下的子目录名。
     case llm = "Qwen3-1.7B-4bit"
     case vl  = "Qwen2.5-VL-3B-Instruct-4bit"
@@ -21,10 +21,10 @@ enum ModelKind: String, CaseIterable {
 
 /// `@unchecked Sendable`:rootURL 是 let,方法只读 filesystem(线程安全),
 /// 可被任意 actor / Task 跨边界访问。
-/// `nonisolated(unsafe) shared`:项目开启 `-default-isolation=MainActor` 后
-/// static 默认 MainActor 隔离,跨 actor 访问需要 await。这里手动 opt-out。
+/// 实例方法显式 `nonisolated`:项目开了 `SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor`,
+/// 默认会把方法推到 MainActor,导致从 `AIRuntime` 等 actor 调用报错。
 final class ModelStore: @unchecked Sendable {
-    nonisolated(unsafe) static let shared: ModelStore = {
+    nonisolated static let shared: ModelStore = {
         do {
             let appSupport = try FileManager.default.url(
                 for: .applicationSupportDirectory,
@@ -46,16 +46,16 @@ final class ModelStore: @unchecked Sendable {
         try FileManager.default.createDirectory(at: rootURL, withIntermediateDirectories: true)
     }
 
-    func localURL(for kind: ModelKind) -> URL {
+    nonisolated func localURL(for kind: ModelKind) -> URL {
         rootURL.appendingPathComponent(kind.rawValue, isDirectory: true)
     }
 
-    func isReady(_ kind: ModelKind) -> Bool {
+    nonisolated func isReady(_ kind: ModelKind) -> Bool {
         let sentinel = localURL(for: kind).appendingPathComponent(kind.sentinelFilename)
         return FileManager.default.fileExists(atPath: sentinel.path)
     }
 
-    func totalBytes(for kind: ModelKind) -> Int {
+    nonisolated func totalBytes(for kind: ModelKind) -> Int {
         let folder = localURL(for: kind)
         guard let enumerator = FileManager.default.enumerator(
             at: folder,
@@ -71,7 +71,7 @@ final class ModelStore: @unchecked Sendable {
     }
 
     /// Demo 现场旁路:从 Bundle 拷贝预装模型(W6 才真正使用,本周占位)
-    func seedFromBundle(_ kind: ModelKind) throws {
+    nonisolated func seedFromBundle(_ kind: ModelKind) throws {
         guard let bundleURL = Bundle.main.url(forResource: kind.rawValue, withExtension: nil) else {
             #if DEBUG
             assertionFailure("Bundle 缺少 \(kind.rawValue),检查资源是否加入 target")

康康/Persistence/FileVault.swift

@@ -9,10 +9,9 @@ enum FileVaultError: Error {
 }
 
 /// `@unchecked Sendable`:rootURL 是 let,方法只 I/O 到沙盒目录(线程安全),
-/// 可被任意 actor / Task 跨边界访问。
-/// `nonisolated(unsafe) shared`:见 ModelStore 同款注释。
+/// 可被任意 actor / Task 跨边界访问。实例方法显式 `nonisolated`,见 ModelStore 同款注释。
 final class FileVault: @unchecked Sendable {
-    nonisolated(unsafe) static let shared: FileVault = {
+    nonisolated static let shared: FileVault = {
         do {
             let appSupport = try FileManager.default.url(
                 for: .applicationSupportDirectory,
@@ -45,7 +44,7 @@ final class FileVault: @unchecked Sendable {
 
     // MARK: - Path Safety
 
-    private func resolveSafePath(_ relativePath: String) throws -> URL {
+    nonisolated private func resolveSafePath(_ relativePath: String) throws -> URL {
         guard !relativePath.contains("/"),
               !relativePath.contains(".."),
               !relativePath.isEmpty else {
@@ -60,7 +59,7 @@ final class FileVault: @unchecked Sendable {
 
     // MARK: - Public API
 
-    func writeJPEG(_ image: UIImage, quality: CGFloat = 0.85) throws -> SavedAsset {
+    nonisolated func writeJPEG(_ image: UIImage, quality: CGFloat = 0.85) throws -> SavedAsset {
         guard let data = image.jpegData(compressionQuality: quality) else {
             throw FileVaultError.writeFailed
         }
@@ -70,7 +69,7 @@ final class FileVault: @unchecked Sendable {
         return SavedAsset(relativePath: filename, bytes: data.count)
     }
 
-    func loadImage(relativePath: String) throws -> UIImage {
+    nonisolated func loadImage(relativePath: String) throws -> UIImage {
         let url = try resolveSafePath(relativePath)
         let data: Data
         do {
@@ -82,7 +81,7 @@ final class FileVault: @unchecked Sendable {
         return image
     }
 
-    func remove(relativePath: String) throws {
+    nonisolated func remove(relativePath: String) throws {
         let url = try resolveSafePath(relativePath)
         do {
             try FileManager.default.removeItem(at: url)
@@ -91,7 +90,7 @@ final class FileVault: @unchecked Sendable {
         }
     }
 
-    func wipe() throws {
+    nonisolated func wipe() throws {
         let fm = FileManager.default
         let contents = try fm.contentsOfDirectory(at: rootURL, includingPropertiesForKeys: nil)
         for url in contents {