Stop macOS crashes while opening and stepping through exercises.

Co-authored-by: Cursor <cursoragent@cursor.com>

ios/Graduately/AppModel.swift

@@ -10,7 +10,9 @@ final class AppModel: ObservableObject {
     @Published var mode: ColorMode
     @Published var lang: UiLang
     @Published var tab: AppTab = .practice
-    @Published var practicePath: [Route] = []
+    @Published var practicePath = NavigationPath()
+    /// Bumps whenever a full path replace is scheduled, so a queued push cannot land afterwards.
+    private var pathGeneration = 0
     @Published var searchQuery = ""
     @Published var tick = 0
     @Published var update = UpdateState()
@@ -48,13 +50,17 @@ final class AppModel: ObservableObject {
         case .stats:
             tab = .progress
         case .welcome, .subjects:
-            tab = .practice
-            practicePath = []
+            showPracticeRoot()
         default:
             applyPracticeRoute(r, replace: practicePath.isEmpty)
         }
     }
 
+    func showPracticeRoot() {
+        tab = .practice
+        schedulePracticePath(NavigationPath())
+    }
+
     func goPage(_ page: String?) {
         guard let page, let r = routeFromPage(page) else { return }
         go(r)
@@ -66,8 +72,7 @@ final class AppModel: ObservableObject {
         case .stats:
             tab = .progress
         case .welcome, .subjects:
-            tab = .practice
-            practicePath = []
+            showPracticeRoot()
         default:
             // Switching tabs and assigning a deep NavigationStack path in the
             // same turn crashes SwiftUI on macOS (boundPathChange / unexpectedError).
@@ -76,18 +81,31 @@ final class AppModel: ObservableObject {
     }
 
     /// Sets the practice tab path safely, especially when jumping from Search.
+    ///
+    /// The sidebar-style tab view keeps one navigation column for every tab.
+    /// A typed `[Route]` path does not match the other tabs, so the column
+    /// traps in `boundPathChange` while an exercise is being opened. The path
+    /// is therefore type-erased, and a push is applied on the next turn instead
+    /// of replacing the whole stack during the click.
     private func applyPracticeRoute(_ r: Route, replace: Bool) {
-        let stack = replace ? r.stack : (practicePath + [r])
-        if !replace, practicePath.last == r { return }
         let switching = tab != .practice
         tab = .practice
         if switching || replace {
-            practicePath = []
-            DispatchQueue.main.async { [weak self] in
-                self?.practicePath = stack
-            }
+            schedulePracticePath(NavigationPath(r.stack))
         } else {
-            practicePath = stack
+            let generation = pathGeneration
+            DispatchQueue.main.async { [weak self] in
+                guard let self, self.pathGeneration == generation else { return }
+                self.practicePath.append(r)
+            }
+        }
+    }
+
+    private func schedulePracticePath(_ path: NavigationPath) {
+        pathGeneration += 1
+        practicePath = NavigationPath()
+        DispatchQueue.main.async { [weak self] in
+            self?.practicePath = path
         }
     }
 

ios/Graduately/GraduatelyApp.swift

@@ -17,6 +17,9 @@ struct GraduatelyApp: App {
 
 struct NativeRoot: View {
     @ObservedObject var vm: AppModel
+    @State private var progressPath = NavigationPath()
+    @State private var settingsPath = NavigationPath()
+    @State private var searchPath = NavigationPath()
 
     var body: some View {
         Group {
@@ -49,17 +52,17 @@ struct NativeRoot: View {
                 }
             }
             Tab(vm.tr("stats"), systemImage: "chart.bar.fill", value: .progress) {
-                NavigationStack {
+                NavigationStack(path: $progressPath) {
                     StatsScreen(vm: vm)
                 }
             }
             Tab(vm.tr("settings"), systemImage: "gearshape.fill", value: .settings) {
-                NavigationStack {
+                NavigationStack(path: $settingsPath) {
                     SettingsScreen(vm: vm)
                 }
             }
             Tab(vm.tr("search"), systemImage: "magnifyingglass", value: .search) {
-                NavigationStack {
+                NavigationStack(path: $searchPath) {
                     SearchScreen(vm: vm)
                 }
             }

macos/Graduately/GraduatelyApp.swift

@@ -16,8 +16,7 @@ struct GraduatelyApp: App {
             CommandGroup(replacing: .newItem) {}
             CommandGroup(after: .sidebar) {
                 Button(vm.tr("search_home")) {
-                    vm.tab = .practice
-                    vm.practicePath = []
+                    vm.showPracticeRoot()
                 }
                 .keyboardShortcut("1", modifiers: [.command])
                 Button(vm.tr("stats")) {
@@ -47,6 +46,9 @@ struct GraduatelyApp: App {
 
 struct MacRoot: View {
     @ObservedObject var vm: AppModel
+    @State private var progressPath = NavigationPath()
+    @State private var settingsPath = NavigationPath()
+    @State private var searchPath = NavigationPath()
 
     var body: some View {
         tabs
@@ -77,17 +79,17 @@ struct MacRoot: View {
                 }
             }
             Tab(vm.tr("stats"), systemImage: "chart.bar.fill", value: AppTab.progress) {
-                NavigationStack {
+                NavigationStack(path: $progressPath) {
                     StatsScreen(vm: vm)
                 }
             }
             Tab(vm.tr("settings"), systemImage: "gearshape.fill", value: AppTab.settings) {
-                NavigationStack {
+                NavigationStack(path: $settingsPath) {
                     SettingsScreen(vm: vm)
                 }
             }
             Tab(vm.tr("search"), systemImage: "magnifyingglass", value: AppTab.search, role: .search) {
-                NavigationStack {
+                NavigationStack(path: $searchPath) {
                     SearchScreen(vm: vm)
                 }
             }