feat(ipad): W1-W3 — adaptive split-view layout + finding fixes

T-iPad-2: AdaptiveRootView/LayoutPolicy (sole size-class decision), SplitRootView
(NavigationSplitView sidebar+detail), StackRootView (iPhone path verbatim, zero
regression); privacy shade hoisted to shared ZStack top for both branches
T-iPad-3: KeyBarVisibility predicate (hide when hardware keyboard present),
pointer context menu (copy/new-in-cwd/kill, all via existing channels)
T-iPad-4: Projects multi-column grid on iPad (idiom-gated), adaptive sheet detents
T-iPad-5 findings (4/4 fixed): kill onKillSession thread-through +
AppCoordinator.killCurrentSession; split route-gated to .sessions (iPad first-run
pairing); continue-last banner in split sidebar; iPad XCUITest deferred (covered
by SidebarSelectionTests)
Verified: iPhone 16 277 + iPad Pro 11 278 tests green; packages 261 + integration 10;
zero changes under ios/Packages, src/, public/

ios/App/WebTerm/Screens/ProjectsScreen.swift

@@ -11,14 +11,26 @@ struct ProjectsScreen: View {
     @Bindable var viewModel: ProjectsViewModel
     /// "在此仓库开新会话" 导航钩子（AppCoordinator.openProject 消费）。
     var onOpen: (ProjectOpenRequest) -> Void = { _ in }
+    /// T-iPad-4 · 设备 idiom 只在此读一次，交给 `ProjectsGridLayout`/
+    /// `ProjectsSheetSizing` 决策（视图里零散落条件）。iPhone → 现有单列 List
+    /// （字节级不变）；iPad → 多列网格 + 卡片式 sheet detents。idiom 是设备常量、
+    /// 运行期不变，故非 @Environment 即可。见 `ProjectsLayout` 注释解释为何用
+    /// idiom 而非 size class（iPad 表单 sheet 内部恒 compact）。
+    private var idiom: UIUserInterfaceIdiom { UIDevice.current.userInterfaceIdiom }
 
     private enum Metrics {
         static let rowSpacing: CGFloat = 2
         static let chipSpacing: CGFloat = 6
+        // T-iPad-4 · 多列网格专属度量 —— 只走 iPad（.pad）分支，iPhone 不受影响。
+        static let gridSectionSpacing: CGFloat = 12
+        static let gridPadding: CGFloat = 16
+        static let gridCardVerticalPadding: CGFloat = 8
+        static let gridCardHorizontalPadding: CGFloat = 10
+        static let gridCardCornerRadius: CGFloat = 10
     }
 
     var body: some View {
-        list
+        adaptiveContent
             .navigationTitle(ProjectsCopy.title)
             .navigationBarTitleDisplayMode(.inline)
             .searchable(text: $viewModel.searchText, prompt: ProjectsCopy.searchPrompt)
@@ -36,6 +48,22 @@ struct ProjectsScreen: View {
                     onOpenClaude: { viewModel.requestOpenClaude(cwd: $0) }
                 )
             }
+            // T-iPad-4 · iPhone 透传（现有全高 sheet 字节级不变）；iPad 套
+            // 卡片式 detents（不铺满大屏）。
+            .adaptiveProjectsSheetDetents(idiom: idiom)
+    }
+
+    // MARK: - 自适应容器（唯一 idiom 消费点，经 ProjectsGridLayout）
+
+    /// iPhone → 现有单列 `list`（原样复用，字节级零回归）；iPad → 多列
+    /// `gridList`。分组/折叠/收藏/prefs 往返全部是同一 `ProjectsViewModel`
+    /// 逻辑，两条路径只换视觉容器。
+    @ViewBuilder private var adaptiveContent: some View {
+        if ProjectsGridLayout.usesGrid(idiom: idiom) {
+            gridList
+        } else {
+            list
+        }
     }
 
     // MARK: - List
@@ -61,6 +89,75 @@ struct ProjectsScreen: View {
         }
     }
 
+    // MARK: - Grid（regular 宽度：多列网格）
+
+    /// iPad 分栏/大屏下的多列网格。列数由 `ProjectsGridLayout.columnCount` 按
+    /// **可用宽度**（GeometryReader）决定；分组头/折叠/收藏/行渲染全部复用 List
+    /// 路径的同名 builder（`groupHeader`/`projectRow`/`errorRows`）—— 只换外层
+    /// 容器，分组/收藏/prefs 往返逻辑零改。
+    private var gridList: some View {
+        GeometryReader { proxy in
+            let columns = ProjectsGridLayout.columnCount(
+                availableWidth: proxy.size.width,
+                idiom: idiom
+            )
+            ScrollView {
+                LazyVStack(alignment: .leading, spacing: Metrics.gridSectionSpacing) {
+                    errorRows
+                    if let message = viewModel.emptyStateMessage {
+                        Text(message)
+                            .foregroundStyle(.secondary)
+                            .frame(maxWidth: .infinity, alignment: .center)
+                    }
+                    ForEach(viewModel.groups) { group in
+                        gridSection(group, columns: columns)
+                    }
+                }
+                .padding(Metrics.gridPadding)
+            }
+            .overlay {
+                if !viewModel.hasLoadedOnce && viewModel.fetchErrorMessage == nil {
+                    ProgressView()
+                }
+            }
+        }
+    }
+
+    @ViewBuilder private func gridSection(_ group: ProjectGroup, columns: Int) -> some View {
+        let isCollapsed = viewModel.isCollapsed(group)
+        VStack(alignment: .leading, spacing: Metrics.rowSpacing) {
+            if group.kind != .flat {
+                groupHeader(group, isCollapsed: isCollapsed)
+                    .padding(.top, Metrics.gridSectionSpacing)
+            }
+            if !isCollapsed {
+                LazyVGrid(
+                    columns: gridColumns(columns),
+                    alignment: .leading,
+                    spacing: Metrics.chipSpacing
+                ) {
+                    ForEach(group.projects, id: \.path) { project in
+                        projectRow(project, group: group)
+                            .padding(.vertical, Metrics.gridCardVerticalPadding)
+                            .padding(.horizontal, Metrics.gridCardHorizontalPadding)
+                            .background(
+                                .quaternary,
+                                in: RoundedRectangle(cornerRadius: Metrics.gridCardCornerRadius)
+                            )
+                    }
+                }
+            }
+        }
+    }
+
+    /// 等宽弹性列（`columns >= 1` 由 `ProjectsGridLayout` 保证，绝不空网格）。
+    private func gridColumns(_ count: Int) -> [GridItem] {
+        Array(
+            repeating: GridItem(.flexible(), spacing: Metrics.chipSpacing),
+            count: max(count, ProjectsGridLayout.singleColumn)
+        )
+    }
+
     /// 显式错误行（刷新失败留旧列表、prefs 失败降级本地 —— 都要可见）。
     @ViewBuilder private var errorRows: some View {
         ForEach(