修复账号登录后应用直接退出

系统的登录窗口在后台队列上回调结果，而回调闭包写在主线程隔离的方法里，Swift 6 在闭包入口检查执行器，
不在主线程就中止进程：选完 GitHub / Google / Apple 账号应用立即闪退，令牌还没换到，重开也没有登录状态。
回调改为在非隔离的上下文里创建，收到结果后再回到主线程处理；补了在后台队列调用回调的回归测试。

Packages/OpenStatsKit/Package.swift

@@ -30,7 +30,7 @@ let package = Package(
         .testTarget(name: "HelperSharedTests", dependencies: ["HelperShared"]),
         .testTarget(name: "UpdatesTests", dependencies: ["Updates"]),
         .testTarget(name: "AccountSyncTests", dependencies: ["AccountSync"]),
-        .testTarget(name: "OpenStatsUITests", dependencies: ["OpenStatsUI", "Metrics"]),
+        .testTarget(name: "OpenStatsUITests", dependencies: ["OpenStatsUI", "Metrics", "AccountSync"]),
         .testTarget(name: "LocalizationTests", dependencies: ["Localization"]),
     ],
     swiftLanguageModes: [.v6]

Packages/OpenStatsKit/Sources/OpenStatsUI/State/SyncController.swift

@@ -116,9 +116,8 @@ public final class SyncController {
         let verifier = PKCE.verifier()
         let url = client.loginURL(provider: provider, challenge: PKCE.challenge(for: verifier))
         let anchor = AnchorProvider(anchor: presentationAnchor)
-        let session = ASWebAuthenticationSession(url: url, callbackURLScheme: SyncClient.callbackScheme) { [weak self] callback, error in
-            Task { @MainActor in self?.finishSignIn(callback: callback, error: error, verifier: verifier) }
-        }
+        let session = ASWebAuthenticationSession(url: url, callbackURLScheme: SyncClient.callbackScheme,
+                                                 completionHandler: Self.completionHandler(for: self, verifier: verifier))
         session.presentationContextProvider = anchor
         // 保留浏览器里已登录的第三方账号，用户不必再输一次密码
         session.prefersEphemeralWebBrowserSession = false
@@ -132,6 +131,15 @@ public final class SyncController {
         }
     }
 
+    /// 登录结束时系统在它自己的 XPC 队列上回调，不在主线程。这个闭包必须在非隔离的上下文里创建：
+    /// 直接写在 signIn 里会继承 @MainActor 隔离，Swift 6 在闭包入口检查执行器，发现不在主线程就中止进程
+    /// （选完账号应用直接退出，令牌还没换到，重开也没有登录状态）
+    nonisolated static func completionHandler(for controller: SyncController, verifier: String) -> @Sendable (URL?, Error?) -> Void {
+        { [weak controller] callback, error in
+            Task { @MainActor in controller?.finishSignIn(callback: callback, error: error, verifier: verifier) }
+        }
+    }
+
     public func cancelSignIn() {
         authSession?.cancel()
         authSession = nil

Packages/OpenStatsKit/Tests/OpenStatsUITests/OpenStatsUITests.swift

@@ -1,3 +1,4 @@
+import AccountSync
 import Foundation
 @testable import Metrics
 import Testing
@@ -387,3 +388,28 @@ private func isolatedDefaults() -> UserDefaults {
         #expect(ranking.ranked(limit: 2).map(\.id) == ["z", "x"])
     }
 }
+
+@MainActor
+@Suite struct SyncSignInTests {
+    /// 系统在后台的 XPC 队列上回调登录结果。回调闭包如果带着主线程隔离，Swift 6 会在入口处中止进程，
+    /// 表现为选完账号应用直接退出；这里在后台队列调用一次，能跑完并回到主线程处理就算通过
+    @Test func completionHandlerMayRunOffMainThread() async {
+        let controller = SyncController(settings: AppSettings(defaults: isolatedDefaults()), defaults: isolatedDefaults(),
+                                        tokens: MemoryTokenStore())
+        let handler = SyncController.completionHandler(for: controller, verifier: "verifier")
+        await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
+            DispatchQueue.global().async {
+                handler(nil, nil)
+                continuation.resume()
+            }
+        }
+        // 没有回调地址按失败处理；处理发生在主线程的下一个任务里，稍等一下
+        for _ in 0..<100 where controller.phase == .idle {
+            try? await Task.sleep(for: .milliseconds(10))
+        }
+        guard case .failed = controller.phase else {
+            Issue.record("回调之后 phase 应为 failed，实际是 \(controller.phase)")
+            return
+        }
+    }
+}