From 4e9fef02a574f16bb6fe3f7cef4f967e009d2a5d Mon Sep 17 00:00:00 2001
From: Ariver <shanghai3168@gmail.com>
Date: Thu, 18 Jun 2026 20:48:55 +0800
Subject: [PATCH] Add App Shelf index markers

---
 C1.source/Sources/Aligner/QuickSwitchRootView.swift | 2671 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
 1 files changed, 2,375 insertions(+), 296 deletions(-)

diff --git a/C1.source/Sources/Aligner/QuickSwitchRootView.swift b/C1.source/Sources/Aligner/QuickSwitchRootView.swift
index 7c3bd30..f127082 100644
--- a/C1.source/Sources/Aligner/QuickSwitchRootView.swift
+++ b/C1.source/Sources/Aligner/QuickSwitchRootView.swift
@@ -22,11 +22,16 @@
     private let waterfallLayer = CALayer()
     private let waterfallContentLayer = CALayer()
     private lazy var closeConfirmationLayers = makeCloseConfirmationLayers()
+    private let closeFeedbackLayer = CALayer()
+    private let closeFeedbackTextLayer = CATextLayer()
+    private let viewModeToggleButtonLayer = CALayer()
+    private let viewModeToggleIconLayer = CALayer()
     private let appIconProvider: any AppIconProviderProtocol = WorkspaceAppIconProvider()
     private let skeletonThumbnailProvider = NativeSkeletonThumbnailProvider(size: NSSize(width: 160, height: 96))
     private var screenshotSourcesByWindowID: [UInt32: ScreenshotResolutionSource] = [:]
     private var screenshotSkippedReasonsByWindowID: [UInt32: String] = [:]
     private var currentViewModel: QuickSwitchViewModel?
+    private var spaceLaneDisplayGroups: [SpaceLaneDisplayGroupLayers] = []
     private var spaceLaneSegments: [SpaceLaneSegmentLayers] = []
     private var spaceLaneContentWidth: CGFloat = 0
     private var spaceLaneScrollOffset: CGFloat = 0
@@ -40,16 +45,26 @@
     private var hoveredSpaceID: UInt64?
     private var hoveredCloseTarget: CloseTarget?
     private var pendingCloseTarget: CloseTarget?
+    private var pendingCloseRequest: QuickSwitchCloseRequest?
     private var pendingCloseOptOut = false
     private var closeConfirmationArrowEdge: CloseConfirmationArrowEdge?
     private var closeConfirmationRequired = true
+    private var closeFeedback: CloseFeedback?
+    private var closeFeedbackHideTask: Task<Void, Never>?
+    private var isViewModeToggleButtonHovered = false
+    private var suppressViewModeToggleHoverPreview = false
+    private var hoverTarget: HoverTarget = .none
+    private var hoverTargetSource: HoverTargetSource = .event
     private var hoveredSpaceLaneID: UInt64?
     private var focusedSpaceID: UInt64?
     private var debugHoveredAppGroupIndex: Int?
     private var waterfallColumns: [WaterfallColumnLayers] = []
+    private var waterfallViewMode: QuickSwitchWaterfallViewMode = .verticalColumns
     private var waterfallContentWidth: CGFloat = 0
     private var waterfallScrollOffset: CGFloat = 0
     private var waterfallColumnScrollOffsets: [Int: CGFloat] = [:]
+    private var horizontalMasonryContentHeight: CGFloat = 0
+    private var horizontalMasonryScrollOffset: CGFloat = 0
     private var currentSelection: QuickSwitchSelection?
     private var columnSelectionHistory: [Int: Int] = [:]
     private var keyboardCommandsApplied: [String] = []
@@ -70,8 +85,17 @@
     private var keyboardResponseLatencyMilliseconds: [Double] = []
     private var mouseResponseLatencyMilliseconds: [Double] = []
     private var hoverResponseLatencyMilliseconds: [Double] = []
+    private var lastProjectionTransitionMovedLayerCount = 0
+    private var lastProjectionTransitionFadeInLayerCount = 0
+    private var lastProjectionTransitionFadeOutLayerCount = 0
+    private var lastProjectionTransitionDurationMilliseconds: Double = 0
+    private var suppressEventInput = false
+    private var suppressEventBackgroundClicks = false
     var onEscape: (() -> Void)?
     var onCommitSelection: ((QuickSwitchSelection, QuickSwitchCommitSource) -> Void)?
+    var onSpaceLaneClick: ((UInt64, Int) -> Void)?
+    var onBackgroundClick: (() -> Bool)?
+    var onToggleWaterfallViewMode: (() -> Void)?
     var onRequestClose: ((QuickSwitchCloseRequest) -> Void)?
     var onCloseConfirmationDisabled: (() -> Void)?
 
@@ -108,9 +132,92 @@
         let cancelButtonTextLayer: CATextLayer
     }
 
+    private struct CloseFeedback: Equatable, Sendable {
+        enum Kind: String, Sendable {
+            case progress
+            case failure
+        }
+
+        let kind: Kind
+        let message: String
+        let targetKind: String
+        let appGroupIndex: Int
+        let windowID: UInt32?
+    }
+
     private enum CloseConfirmationArrowEdge: String {
         case left
         case right
+    }
+
+    private enum HoverTarget: Equatable {
+        case none
+        case space(UInt64)
+        case app(Int)
+        case window(appGroupIndex: Int, windowID: UInt32, spaceID: UInt64?)
+
+        var kindDescription: String {
+            switch self {
+            case .none:
+                return "none"
+            case .space:
+                return "space"
+            case .app:
+                return "app"
+            case .window:
+                return "window"
+            }
+        }
+
+        var appGroupIndex: Int? {
+            switch self {
+            case .app(let appGroupIndex):
+                return appGroupIndex
+            case .window(let appGroupIndex, _, _):
+                return appGroupIndex
+            case .none, .space:
+                return nil
+            }
+        }
+
+        var windowID: UInt32? {
+            switch self {
+            case .window(_, let windowID, _):
+                return windowID
+            case .none, .space, .app:
+                return nil
+            }
+        }
+
+        var spaceID: UInt64? {
+            switch self {
+            case .space(let spaceID):
+                return spaceID
+            case .window(_, _, let spaceID):
+                return spaceID
+            case .none, .app:
+                return nil
+            }
+        }
+
+        var spaceLaneID: UInt64? {
+            guard case .space(let spaceID) = self else { return nil }
+            return spaceID
+        }
+
+        var shouldAlignWaterfallWithAppShelf: Bool {
+            switch self {
+            case .app:
+                return true
+            case .none, .space, .window:
+                return false
+            }
+        }
+    }
+
+    private enum HoverTargetSource: String {
+        case event
+        case debug
     }
 
     private struct SpaceLaneSegmentLayers {
@@ -119,14 +226,22 @@
         let labelLayer: CATextLayer
         let countLayer: CATextLayer
         let appLayer: CATextLayer
+        let splitAppLayers: [CATextLayer]
         let windowBlocks: [CALayer]
         let fullscreenMarkerLayer: CALayer?
+    }
+
+    private struct SpaceLaneDisplayGroupLayers {
+        let display: QuickSwitchDisplayViewModel
+        let containerLayer: CALayer
+        let segments: [SpaceLaneSegmentLayers]
     }
 
     private struct AppShelfItemLayers {
         let item: QuickSwitchAppShelfItemViewModel
         let containerLayer: CALayer
         let backgroundLayer: CALayer
+        let indexLayer: CATextLayer
         let iconLayer: CALayer
         let labelLayer: CATextLayer
         let badgeLayer: CATextLayer
@@ -161,6 +276,22 @@
         let closeButton: CloseButtonLayers
     }
 
+    private struct ProjectionLayerSnapshot {
+        let layer: CALayer
+        let frame: CGRect
+    }
+
+    private struct ProjectionColumnSnapshot {
+        let layer: CALayer
+        let frame: CGRect
+        let cardsByWindowID: [UInt32: ProjectionLayerSnapshot]
+    }
+
+    private struct ProjectionTransitionSnapshot {
+        let appShelfItemsByAppGroupIndex: [Int: ProjectionLayerSnapshot]
+        let waterfallColumnsByAppGroupIndex: [Int: ProjectionColumnSnapshot]
+    }
+
     private enum AppShelfMetrics {
         static let normalIconSize: CGFloat = 56
         static let hoverIconSize: CGFloat = 68
@@ -169,6 +300,10 @@
         static let normalGap: CGFloat = 16
         static let minGap: CGFloat = 8
         static let maxRows = 2
+        static let indexFontSize: CGFloat = 15
+        static let compressedIndexFontSize: CGFloat = 13
+        static let indexWidth: CGFloat = 16
+        static let indexHeight: CGFloat = 18
     }
 
     private enum RootLayoutMetrics {
@@ -179,16 +314,48 @@
         static let bottomMargin: CGFloat = 34
     }
 
+    private enum ViewModeToggleMetrics {
+        static let hitSize: CGFloat = 34
+        static let visualSize: CGFloat = 30
+        static let cornerRadius: CGFloat = 9
+        static let iconInset: CGFloat = 7
+        static let glyphLineWidth: CGFloat = 1.65
+        static let glyphCornerRadius: CGFloat = 2.1
+        static let selectedShadowRadius: CGFloat = 10
+        static let idleShadowRadius: CGFloat = 5
+    }
+
+    private enum ViewModeToggleVisualState: String {
+        case horizontalAvailable = "H1"
+        case horizontalSelected = "H2"
+        case verticalAvailable = "Z1"
+        case verticalSelected = "Z2"
+    }
+
     private enum WaterfallMetrics {
         static let gap: CGFloat = 16
         static let columnWidth: CGFloat = 252
         static let columnMinWidth: CGFloat = 220
         static let columnMaxWidth: CGFloat = 292
-        static let columnPadding: CGFloat = 12
+        static let contentHorizontalPadding: CGFloat = 0
+        static let columnHorizontalPadding: CGFloat = 0
+        static let columnVerticalPadding: CGFloat = 0
+        static let columnHeaderTextInset: CGFloat = 12
         static let headerHeight: CGFloat = 34
         static let cardHeight: CGFloat = 138
         static let cardGap: CGFloat = 12
         static let revealPadding: CGFloat = 24
+        static let horizontalRevealPadding: CGFloat = 0
+    }
+
+    private enum HorizontalMasonryMetrics {
+        static let horizontalPadding: CGFloat = 12
+        static let verticalPadding: CGFloat = 0
+        static let horizontalGap: CGFloat = 16
+        static let verticalGap: CGFloat = WaterfallMetrics.cardGap
+        static let cardMinWidth: CGFloat = 220
+        static let cardMaxWidth: CGFloat = 320
+        static let cardHeight: CGFloat = WaterfallMetrics.cardHeight
     }
 
     private enum WaterfallHorizontalIntent {
@@ -200,6 +367,16 @@
         static let tolerance: CGFloat = 1
         static let animationDuration: CFTimeInterval = 0.18
         static let animationTimingName = CAMediaTimingFunctionName.easeOut
+    }
+
+    private enum SpaceLaneMetrics {
+        static let horizontalPadding: CGFloat = 0
+        static let groupGap: CGFloat = 36
+        static let groupHorizontalPadding: CGFloat = 24
+        static let groupVerticalPadding: CGFloat = 6
+        static let segmentGap: CGFloat = 12
+        static let segmentMinWidth: CGFloat = 96
+        static let segmentMaxWidth: CGFloat = 150
     }
 
     override init(frame frameRect: NSRect) {
@@ -231,7 +408,7 @@
 
         let trackingArea = NSTrackingArea(
             rect: bounds,
-            options: [.activeInKeyWindow, .mouseMoved, .mouseEnteredAndExited, .inVisibleRect],
+            options: [.activeAlways, .mouseMoved, .mouseEnteredAndExited, .inVisibleRect],
             owner: self,
             userInfo: nil
         )
@@ -247,6 +424,13 @@
     }
 
     override func keyDown(with event: NSEvent) {
+        if suppressEventInput {
+            DevelopmentDiagnostics.log("quickSwitch.view.keyDown.ignoredForDebugSequence", [
+                "keyCode": event.keyCode
+            ])
+            return
+        }
+
         switch event.keyCode {
         case TriggerKeyCode.escape where Self.shouldDismissOnEscape(event):
             onEscape?()
@@ -268,6 +452,8 @@
     }
 
     override func scrollWheel(with event: NSEvent) {
+        refreshHoverTarget(at: event.locationInWindow)
+
         let dominantDelta = abs(event.scrollingDeltaX) >= abs(event.scrollingDeltaY)
             ? event.scrollingDeltaX
             : event.scrollingDeltaY
@@ -287,6 +473,15 @@
         }
 
         if shouldScrollWaterfall(for: event) {
+            if isHorizontalMasonryMode {
+                let currentOffset = horizontalMasonryScrollOffset
+                horizontalMasonryScrollOffset = clampedHorizontalMasonryOffset(
+                    currentOffset - event.scrollingDeltaY
+                )
+                needsLayout = true
+                return
+            }
+
             if abs(event.scrollingDeltaX) >= abs(event.scrollingDeltaY), waterfallAlignmentScrollable {
                 waterfallScrollOffset = clampedWaterfallAlignmentOffset(waterfallScrollOffset - event.scrollingDeltaX)
                 needsLayout = true
@@ -313,52 +508,53 @@
     override func mouseMoved(with event: NSEvent) {
         guard debugHoveredAppGroupIndex == nil else { return }
 
+        let toggleHovered = viewModeToggleButtonContains(windowLocation: event.locationInWindow)
+        if !toggleHovered {
+            suppressViewModeToggleHoverPreview = false
+        }
+        let shouldShowToggleHoverPreview = toggleHovered && !suppressViewModeToggleHoverPreview
+        if isViewModeToggleButtonHovered != shouldShowToggleHoverPreview {
+            isViewModeToggleButtonHovered = shouldShowToggleHoverPreview
+            needsLayout = true
+        }
+        if toggleHovered {
+            hoveredCloseTarget = nil
+            setHoverTarget(.none)
+            return
+        }
+
         let closeTarget = closeButtonTarget(at: event.locationInWindow)
         if hoveredCloseTarget != closeTarget {
             hoveredCloseTarget = closeTarget
             needsLayout = true
         }
-
-        if let segment = spaceLaneSegment(at: event.locationInWindow) {
-            hoverSpaceLaneSegment(segment)
-            return
-        }
-
-        if let card = waterfallCard(at: event.locationInWindow) {
-            hoveredSpaceLaneID = nil
-            updateHoverState(
-                appGroupIndex: card.item.appGroupIndex,
-                windowID: card.item.window.id,
-                spaceID: card.item.primarySpaceID
-            )
-            return
-        }
-
-        if let item = appShelfItem(at: event.locationInWindow) {
-            hoveredSpaceLaneID = nil
-            updateHoverState(
-                appGroupIndex: item.item.appGroupIndex,
-                windowID: nil,
-                spaceID: nil,
-                alignsWaterfallWithAppShelf: true
-            )
-            return
-        }
-
-        hoveredSpaceLaneID = nil
-        hoveredCloseTarget = nil
-        updateHoverState(appGroupIndex: nil, windowID: nil, spaceID: nil)
+        refreshHoverTarget(at: event.locationInWindow)
     }
 
     override func mouseExited(with event: NSEvent) {
         guard debugHoveredAppGroupIndex == nil else { return }
-        hoveredSpaceLaneID = nil
+        isViewModeToggleButtonHovered = false
+        suppressViewModeToggleHoverPreview = false
         hoveredCloseTarget = nil
-        updateHoverState(appGroupIndex: nil, windowID: nil, spaceID: nil)
+        setHoverTarget(.none)
     }
 
     override func mouseDown(with event: NSEvent) {
+        if suppressEventInput {
+            DevelopmentDiagnostics.log("quickSwitch.view.mouseDown.ignoredForDebugSequence", [
+                "x": event.locationInWindow.x,
+                "y": event.locationInWindow.y,
+                "bounds": NSStringFromRect(bounds)
+            ])
+            return
+        }
+
         if handleCloseConfirmationMouseDown(at: event.locationInWindow) {
+            return
+        }
+
+        if viewModeToggleButtonContains(windowLocation: event.locationInWindow) {
+            clickViewModeToggleButton(source: "mouse")
             return
         }
 
@@ -373,7 +569,7 @@
         }
 
         if let segment = spaceLaneSegment(at: event.locationInWindow) {
-            clickSpaceLaneSegment(segment)
+            clickSpaceLaneSegment(segment, clickCount: max(1, event.clickCount))
             return
         }
 
@@ -387,15 +583,16 @@
             "y": event.locationInWindow.y,
             "bounds": NSStringFromRect(bounds)
         ])
+        if !suppressEventBackgroundClicks, onBackgroundClick?() == true {
+            return
+        }
         super.mouseDown(with: event)
     }
 
     func setDebugHoveredAppGroupIndex(_ index: Int?) {
         debugHoveredAppGroupIndex = index
+        setHoverTarget(.none, source: .debug)
         hoveredAppGroupIndex = index
-        hoveredWindowID = nil
-        hoveredSpaceID = nil
-        hoveredSpaceLaneID = nil
         needsLayout = true
     }
 
@@ -432,6 +629,15 @@
         }
     }
 
+    func setSuppressEventBackgroundClicks(_ suppressed: Bool) {
+        suppressEventBackgroundClicks = suppressed
+    }
+
+    func setSuppressEventInput(_ suppressed: Bool) {
+        suppressEventInput = suppressed
+        suppressEventBackgroundClicks = suppressed
+    }
+
     func beginPerformanceFirstFrameMeasurement() {
         firstFrameMeasurementStart = CACurrentMediaTime()
     }
@@ -457,10 +663,58 @@
         closeConfirmationRequired = required
         if !required {
             pendingCloseTarget = nil
+            pendingCloseRequest = nil
             pendingCloseOptOut = false
             closeConfirmationLayers.containerLayer.isHidden = true
             closeConfirmationArrowEdge = nil
         }
+        needsLayout = true
+    }
+
+    func setWaterfallViewMode(_ mode: QuickSwitchWaterfallViewMode) {
+        guard waterfallViewMode != mode else { return }
+
+        waterfallViewMode = mode
+        waterfallScrollOffset = 0
+        waterfallColumnScrollOffsets = [:]
+        horizontalMasonryScrollOffset = 0
+        horizontalMasonryContentHeight = 0
+        needsLayout = true
+    }
+
+    func showCloseProgress(for request: QuickSwitchCloseRequest) {
+        setCloseFeedback(
+            CloseFeedback(
+                kind: .progress,
+                message: "正在关闭...",
+                targetKind: request.kindDescription,
+                appGroupIndex: request.appGroupIndex,
+                windowID: request.windowID
+            ),
+            autoHideAfter: nil
+        )
+    }
+
+    func showCloseFailure(message: String, for request: QuickSwitchCloseRequest) {
+        setCloseFeedback(
+            CloseFeedback(
+                kind: .failure,
+                message: message,
+                targetKind: request.kindDescription,
+                appGroupIndex: request.appGroupIndex,
+                windowID: request.windowID
+            ),
+            autoHideAfter: 2.75
+        )
+    }
+
+    func clearCloseFeedback() {
+        closeFeedbackHideTask?.cancel()
+        closeFeedbackHideTask = nil
+        closeFeedback = nil
+        closeFeedbackLayer.isHidden = true
+        closeFeedbackLayer.opacity = 0
+        closeFeedbackTextLayer.string = ""
         needsLayout = true
     }
 
@@ -471,7 +725,9 @@
         guard let card = waterfallCardsByWindowID()[windowID] else { return }
         card.thumbnailLayer.contents = resolution.image
         if case .realScreenshot = resolution.source {
-            card.shineLayer.opacity = card.item.window.id == effectiveSelection?.windowID ? 1 : 0
+            let isSelected = card.item.window.id == effectiveSelection?.windowID
+            let isHovered = card.item.window.id == hoveredWindowID
+            card.shineLayer.opacity = shouldShowSelectedVisual(isSelected: isSelected, isHovered: isHovered) ? 1 : 0
         }
         needsLayout = true
     }
@@ -488,48 +744,380 @@
         }
     }
 
+    func effectiveSelectionForProjection() -> QuickSwitchSelection? {
+        effectiveSelection
+    }
+
     func apply(viewModel: QuickSwitchViewModel?) {
+        apply(viewModel: viewModel, preservingInteractionState: false, animatedProjection: false)
+    }
+
+    func applyProjected(viewModel: QuickSwitchViewModel?) {
+        apply(viewModel: viewModel, preservingInteractionState: true, animatedProjection: true)
+    }
+
+    func hoverNextAppGroupIndex(cycleForward: Bool = true) -> Bool {
+        guard !appShelfItems.isEmpty else {
+            return false
+        }
+
+        let orderedIndexes = appShelfItems.map(\.item.appGroupIndex)
+        let sortedIndexes = orderedIndexes
+
+        var currentIndexPosition: Int?
+        if let currentHovered = effectiveHoveredAppGroupIndex {
+            currentIndexPosition = sortedIndexes.firstIndex(of: currentHovered)
+        }
+
+        let nextPosition = currentIndexPosition.map { current in
+            if cycleForward {
+                (current + 1) % sortedIndexes.count
+            } else {
+                (current - 1 + sortedIndexes.count) % sortedIndexes.count
+            }
+        } ?? 0
+
+        let nextAppGroupIndex = sortedIndexes[nextPosition]
+        hoverAppGroup(nextAppGroupIndex)
+        return true
+    }
+
+    private func apply(
+        viewModel: QuickSwitchViewModel?,
+        preservingInteractionState: Bool,
+        animatedProjection: Bool
+    ) {
+        let preservedWindowThumbnails = preservingInteractionState ? cachedThumbnailsByWindowID() : [:]
+        let transitionSnapshot = animatedProjection ? captureProjectionTransitionSnapshot() : nil
+        if !animatedProjection {
+            resetProjectionTransitionReport()
+        }
         currentViewModel = viewModel
-        screenshotSourcesByWindowID = [:]
-        screenshotSkippedReasonsByWindowID = [:]
-        currentSelection = viewModel?.initialSelection
-        columnSelectionHistory = [:]
-        keyboardCommandsApplied = []
-        lastKeyboardCommand = nil
-        tabIgnoredCount = 0
-        lastCommittedSelection = nil
-        lastCommitSource = nil
-        mouseCommandsApplied = []
-        lastMouseCommand = nil
-        lastClickedAppGroupIndex = nil
-        lastAppShelfClickChangedSelection = nil
-        lastClickedWindowID = nil
-        lastSpaceFocusedAppGroupIndex = nil
-        lastSpaceLaneClickSpaceID = nil
-        lastAppShelfScrollSyncedAppGroupIndex = nil
-        hoveredWindowID = nil
-        hoveredSpaceID = nil
-        hoveredCloseTarget = nil
-        pendingCloseTarget = nil
-        pendingCloseOptOut = false
-        closeConfirmationLayers.containerLayer.isHidden = true
-        closeConfirmationArrowEdge = nil
-        hoveredSpaceLaneID = nil
-        focusedSpaceID = nil
-        if debugHoveredAppGroupIndex == nil {
-            hoveredAppGroupIndex = nil
+
+        if preservingInteractionState {
+            currentSelection = validSelection(currentSelection, in: viewModel) ?? viewModel?.initialSelection
+            columnSelectionHistory = columnSelectionHistory.filter { appGroupIndex, _ in
+                viewModel?.waterfallColumns.contains { $0.appGroupIndex == appGroupIndex } == true
+            }
+            if let currentSelection {
+                columnSelectionHistory[currentSelection.appGroupIndex] = currentSelection.windowIndex
+            }
+            hoveredCloseTarget = nil
+            pendingCloseTarget = nil
+            pendingCloseRequest = nil
+            pendingCloseOptOut = false
+            closeConfirmationLayers.containerLayer.isHidden = true
+            closeConfirmationArrowEdge = nil
         } else {
+            screenshotSourcesByWindowID = [:]
+            screenshotSkippedReasonsByWindowID = [:]
+            currentSelection = viewModel?.initialSelection
+            columnSelectionHistory = [:]
+            keyboardCommandsApplied = []
+            lastKeyboardCommand = nil
+            tabIgnoredCount = 0
+            lastCommittedSelection = nil
+            lastCommitSource = nil
+            mouseCommandsApplied = []
+            lastMouseCommand = nil
+            lastClickedAppGroupIndex = nil
+            lastAppShelfClickChangedSelection = nil
+            lastClickedWindowID = nil
+            lastSpaceFocusedAppGroupIndex = nil
+            lastSpaceLaneClickSpaceID = nil
+            lastAppShelfScrollSyncedAppGroupIndex = nil
+            waterfallScrollOffset = 0
+            waterfallColumnScrollOffsets = [:]
+            horizontalMasonryScrollOffset = 0
+            horizontalMasonryContentHeight = 0
+            focusedSpaceID = nil
+            hoveredCloseTarget = nil
+            pendingCloseTarget = nil
+            pendingCloseRequest = nil
+            pendingCloseOptOut = false
+            closeConfirmationLayers.containerLayer.isHidden = true
+            closeConfirmationArrowEdge = nil
+            clearCloseFeedback()
+            setHoverTarget(.none)
             hoveredAppGroupIndex = debugHoveredAppGroupIndex
         }
+
         if let currentSelection {
             columnSelectionHistory[currentSelection.appGroupIndex] = currentSelection.windowIndex
         }
         rebuildSpaceLaneSegments()
         rebuildAppShelfItems()
         rebuildWaterfallColumns()
+
+        if preservingInteractionState {
+            restoreThumbnailsFromCache(preservedWindowThumbnails)
+        }
+
         needsLayout = true
         ensureCurrentSelectionVisible(horizontalIntent: .alignWithAppShelf(animated: false))
         needsLayout = true
+        if animatedProjection, let transitionSnapshot {
+            layoutSubtreeIfNeeded()
+            applyProjectionTransitionAnimations(from: transitionSnapshot)
+        }
+    }
+
+    private func cachedThumbnailsByWindowID() -> [UInt32: Any] {
+        var snapshots: [UInt32: Any] = [:]
+
+        for card in waterfallCardsByWindowID().values {
+            snapshots[card.item.window.id] = card.thumbnailLayer.contents
+        }
+
+        return snapshots
+    }
+
+    private func restoreThumbnailsFromCache(_ cachedThumbnails: [UInt32: Any]) {
+        for card in waterfallCardsByWindowID().values {
+            if let thumbnail = cachedThumbnails[card.item.window.id] {
+                card.thumbnailLayer.contents = thumbnail
+            }
+        }
+    }
+
+    private func validSelection(
+        _ selection: QuickSwitchSelection?,
+        in viewModel: QuickSwitchViewModel?
+    ) -> QuickSwitchSelection? {
+        guard let selection, let viewModel else { return nil }
+
+        for column in viewModel.waterfallColumns {
+            if let card = column.windows.first(where: { $0.window.id == selection.windowID }) {
+                return QuickSwitchSelection(
+                    appGroupIndex: card.appGroupIndex,
+                    windowIndex: card.windowIndex,
+                    windowID: card.window.id
+                )
+            }
+        }
+
+        return nil
+    }
+
+    private func captureProjectionTransitionSnapshot() -> ProjectionTransitionSnapshot {
+        ProjectionTransitionSnapshot(
+            appShelfItemsByAppGroupIndex: Dictionary(
+                uniqueKeysWithValues: appShelfItems.map { item in
+                    (
+                        item.item.appGroupIndex,
+                        ProjectionLayerSnapshot(
+                            layer: item.containerLayer,
+                            frame: item.containerLayer.frame
+                        )
+                    )
+                }
+            ),
+            waterfallColumnsByAppGroupIndex: Dictionary(
+                uniqueKeysWithValues: waterfallColumns.map { column in
+                    (
+                        column.column.appGroupIndex,
+                        ProjectionColumnSnapshot(
+                            layer: column.containerLayer,
+                            frame: column.containerLayer.frame,
+                            cardsByWindowID: Dictionary(
+                                uniqueKeysWithValues: column.cards.map { card in
+                                    (
+                                        card.item.window.id,
+                                        ProjectionLayerSnapshot(
+                                            layer: card.containerLayer,
+                                            frame: card.containerLayer.frame
+                                        )
+                                    )
+                                }
+                            )
+                        )
+                    )
+                }
+            )
+        )
+    }
+
+    private func applyProjectionTransitionAnimations(from snapshot: ProjectionTransitionSnapshot) {
+        let reduceMotion = NSWorkspace.shared.accessibilityDisplayShouldReduceMotion
+        let duration: CFTimeInterval = reduceMotion ? 0.12 : 0.21
+        let timing = CAMediaTimingFunction(name: reduceMotion ? .linear : .easeOut)
+        var movedLayerCount = 0
+        var fadeInLayerCount = 0
+        var fadeOutLayerCount = 0
+
+        for item in appShelfItems {
+            guard let oldSnapshot = snapshot.appShelfItemsByAppGroupIndex[item.item.appGroupIndex] else {
+                if addFadeInAnimation(to: item.containerLayer, duration: duration, timing: timing) {
+                    fadeInLayerCount += 1
+                }
+                continue
+            }
+            if addPositionAnimation(to: item.containerLayer, from: oldSnapshot.frame, duration: duration, timing: timing) {
+                movedLayerCount += 1
+            }
+        }
+
+        let visibleAppGroupIndexes = Set(appShelfItems.map(\.item.appGroupIndex))
+        for (appGroupIndex, oldSnapshot) in snapshot.appShelfItemsByAppGroupIndex
+            where !visibleAppGroupIndexes.contains(appGroupIndex) {
+            if addFadeOutSnapshot(
+                oldSnapshot,
+                to: appShelfContentLayer,
+                frame: oldSnapshot.frame,
+                duration: duration,
+                timing: timing
+            ) {
+                fadeOutLayerCount += 1
+            }
+        }
+
+        for column in waterfallColumns {
+            guard let oldSnapshot = snapshot.waterfallColumnsByAppGroupIndex[column.column.appGroupIndex] else {
+                if addFadeInAnimation(to: column.containerLayer, duration: duration, timing: timing) {
+                    fadeInLayerCount += 1
+                }
+                continue
+            }
+            if addPositionAnimation(to: column.containerLayer, from: oldSnapshot.frame, duration: duration, timing: timing) {
+                movedLayerCount += 1
+            }
+
+            for card in column.cards {
+                guard let oldCardSnapshot = oldSnapshot.cardsByWindowID[card.item.window.id] else {
+                    if addFadeInAnimation(to: card.containerLayer, duration: duration, timing: timing) {
+                        fadeInLayerCount += 1
+                    }
+                    continue
+                }
+                if addPositionAnimation(to: card.containerLayer, from: oldCardSnapshot.frame, duration: duration, timing: timing) {
+                    movedLayerCount += 1
+                }
+            }
+        }
+
+        let visibleColumnsByAppGroupIndex = Dictionary(
+            uniqueKeysWithValues: waterfallColumns.map { ($0.column.appGroupIndex, $0) }
+        )
+        for (appGroupIndex, oldSnapshot) in snapshot.waterfallColumnsByAppGroupIndex {
+            guard let visibleColumn = visibleColumnsByAppGroupIndex[appGroupIndex] else {
+                if addFadeOutSnapshot(
+                    ProjectionLayerSnapshot(layer: oldSnapshot.layer, frame: oldSnapshot.frame),
+                    to: waterfallContentLayer,
+                    frame: oldSnapshot.frame,
+                    duration: duration,
+                    timing: timing
+                ) {
+                    fadeOutLayerCount += 1
+                }
+                continue
+            }
+
+            let visibleWindowIDs = Set(visibleColumn.cards.map(\.item.window.id))
+            for (windowID, oldCardSnapshot) in oldSnapshot.cardsByWindowID
+                where !visibleWindowIDs.contains(windowID) {
+                let absoluteFrame = oldCardSnapshot.frame.offsetBy(
+                    dx: oldSnapshot.frame.minX,
+                    dy: oldSnapshot.frame.minY
+                )
+                if addFadeOutSnapshot(
+                    oldCardSnapshot,
+                    to: waterfallContentLayer,
+                    frame: absoluteFrame,
+                    duration: duration,
+                    timing: timing
+                ) {
+                    fadeOutLayerCount += 1
+                }
+            }
+        }
+
+        lastProjectionTransitionMovedLayerCount = movedLayerCount
+        lastProjectionTransitionFadeInLayerCount = fadeInLayerCount
+        lastProjectionTransitionFadeOutLayerCount = fadeOutLayerCount
+        lastProjectionTransitionDurationMilliseconds = duration * 1_000
+    }
+
+    private func resetProjectionTransitionReport() {
+        lastProjectionTransitionMovedLayerCount = 0
+        lastProjectionTransitionFadeInLayerCount = 0
+        lastProjectionTransitionFadeOutLayerCount = 0
+        lastProjectionTransitionDurationMilliseconds = 0
+    }
+
+    @discardableResult
+    private func addPositionAnimation(
+        to layer: CALayer,
+        from oldFrame: CGRect,
+        duration: CFTimeInterval,
+        timing: CAMediaTimingFunction
+    ) -> Bool {
+        let oldPosition = CGPoint(x: oldFrame.midX, y: oldFrame.midY)
+        let newPosition = layer.position
+        guard abs(oldPosition.x - newPosition.x) > 0.5 || abs(oldPosition.y - newPosition.y) > 0.5 else {
+            return false
+        }
+
+        let animation = CABasicAnimation(keyPath: "position")
+        animation.fromValue = oldPosition
+        animation.toValue = newPosition
+        animation.duration = duration
+        animation.timingFunction = timing
+        animation.isRemovedOnCompletion = true
+        layer.add(animation, forKey: "quickSwitchProjectionPosition")
+        return true
+    }
+
+    @discardableResult
+    private func addFadeInAnimation(
+        to layer: CALayer,
+        duration: CFTimeInterval,
+        timing: CAMediaTimingFunction
+    ) -> Bool {
+        let animation = CABasicAnimation(keyPath: "opacity")
+        animation.fromValue = 0
+        animation.toValue = layer.opacity
+        animation.duration = duration
+        animation.timingFunction = timing
+        animation.isRemovedOnCompletion = true
+        layer.add(animation, forKey: "quickSwitchProjectionFadeIn")
+        return true
+    }
+
+    @discardableResult
+    private func addFadeOutSnapshot(
+        _ snapshot: ProjectionLayerSnapshot,
+        to parentLayer: CALayer,
+        frame: CGRect,
+        duration: CFTimeInterval,
+        timing: CAMediaTimingFunction
+    ) -> Bool {
+        let layer = snapshot.layer
+        layer.removeAllAnimations()
+        layer.removeFromSuperlayer()
+        CATransaction.begin()
+        CATransaction.setDisableActions(true)
+        layer.frame = frame
+        layer.opacity = max(layer.opacity, 0.01)
+        layer.zPosition = max(layer.zPosition, 240)
+        parentLayer.addSublayer(layer)
+        CATransaction.commit()
+
+        let animation = CABasicAnimation(keyPath: "opacity")
+        animation.fromValue = layer.opacity
+        animation.toValue = 0
+        animation.duration = duration
+        animation.timingFunction = timing
+        animation.isRemovedOnCompletion = true
+        CATransaction.begin()
+        CATransaction.setDisableActions(true)
+        layer.opacity = 0
+        CATransaction.commit()
+        layer.add(animation, forKey: "quickSwitchProjectionFadeOut")
+
+        DispatchQueue.main.asyncAfter(deadline: .now() + duration + 0.05) { [weak layer] in
+            layer?.removeFromSuperlayer()
+        }
+        return true
     }
 
     func reportDictionary() -> [String: Any] {
@@ -553,17 +1141,42 @@
             "glassBorderWidth": Double(glassLayer.borderWidth),
             "glassShadowOpacity": Double(glassLayer.shadowOpacity),
             "spaceLaneFrame": dictionary(from: laneLayer.frame),
+            "spaceLaneBackgroundColor": colorDictionary(from: laneLayer.backgroundColor),
+            "spaceLaneCornerRadius": Double(laneLayer.cornerRadius),
             "spaceLaneContentWidth": Double(spaceLaneContentWidth),
             "spaceLaneVisibleWidth": Double(laneLayer.bounds.width),
             "spaceLaneMaxScrollOffset": Double(spaceLaneMaxScrollOffset),
             "spaceLaneScrollable": spaceLaneMaxScrollOffset > 0,
+            "spaceLaneDisplayGroupCount": spaceLaneDisplayGroups.count,
+            "spaceLaneDisplayGroups": spaceLaneDisplayGroupReports(),
             "spaceLaneSegmentCount": spaceLaneSegments.count,
             "spaceLaneLabels": currentViewModel?.displays.flatMap { $0.spaces.map(\.label) } ?? [],
             "spaceLaneSegments": spaceLaneSegmentReports(),
+            "hoverTargetKind": hoverTarget.kindDescription,
+            "hoverTargetSource": hoverTargetSource.rawValue,
             "spaceLaneHoveredSpaceID": hoveredSpaceLaneID ?? NSNull(),
             "spaceLaneFocusedSpaceID": focusedSpaceID ?? NSNull(),
             "activeSpaceFocusID": activeSpaceFocusID ?? NSNull(),
+            "spaceFilterLockedSpaceID": currentViewModel?.lockedSpaceID ?? NSNull(),
+            "spaceFilterActive": currentViewModel?.lockedSpaceID != nil,
+            "viewModeToggleButtonVisible": !viewModeToggleButtonLayer.isHidden,
+            "viewModeToggleButtonHovered": isViewModeToggleButtonHovered,
+            "viewModeToggleHoverPreviewSuppressed": suppressViewModeToggleHoverPreview,
+            "viewModeToggleButtonFrame": dictionary(from: viewModeToggleButtonLayer.frame),
+            "viewModeToggleHitSize": Double(ViewModeToggleMetrics.hitSize),
+            "viewModeToggleVisualSize": Double(ViewModeToggleMetrics.visualSize),
+            "viewModeToggleCurrentMode": waterfallViewMode.rawValue,
+            "viewModeToggleTargetMode": nextWaterfallViewMode.rawValue,
+            "viewModeToggleIconKind": viewModeToggleIconKind,
+            "viewModeToggleVisualState": viewModeToggleVisualState.rawValue,
+            "viewModeToggleStandardBlueColor": colorDictionary(from: viewModeToggleBlueColor.cgColor),
+            "viewModeToggleGlyphLineWidth": Double(ViewModeToggleMetrics.glyphLineWidth),
+            "viewModeToggleAccessibilityLabel": viewModeToggleAccessibilityLabel,
+            "settingsButtonVisible": false,
             "spaceFocusAppGroupIndexes": spaceFocusedAppGroupIndexes(),
+            "appHoverAssociatedSpaceIDs": appHoverAssociatedSpaceIDs.sorted(),
+            "appHoverAssociatedSpaceLabels": appHoverAssociatedSpaceLabels,
+            "windowHoverAssociatedSpaceID": windowHoverAssociatedSpaceID ?? NSNull(),
             "lastSpaceFocusedAppGroupIndex": lastSpaceFocusedAppGroupIndex ?? NSNull(),
             "lastSpaceLaneClickSpaceID": lastSpaceLaneClickSpaceID ?? NSNull(),
             "lastAppShelfScrollSyncedAppGroupIndex": lastAppShelfScrollSyncedAppGroupIndex ?? NSNull(),
@@ -591,13 +1204,19 @@
             "appShelfMinIconSize": Double(AppShelfMetrics.minIconSize),
             "appShelfItems": appShelfItemReports(),
             "waterfallFrame": dictionary(from: waterfallLayer.frame),
+            "waterfallViewMode": waterfallViewMode.rawValue,
             "waterfallContentWidth": Double(waterfallContentWidth),
             "waterfallVisibleWidth": Double(waterfallLayer.bounds.width),
             "waterfallScrollOffset": Double(waterfallScrollOffset),
             "waterfallMaxScrollOffset": Double(waterfallMaxScrollOffset),
+            "horizontalMasonryContentHeight": Double(horizontalMasonryContentHeight),
+            "horizontalMasonryScrollOffset": Double(horizontalMasonryScrollOffset),
+            "horizontalMasonryMaxScrollOffset": Double(horizontalMasonryMaxScrollOffset),
+            "horizontalMasonryScrollable": horizontalMasonryMaxScrollOffset > 0,
             "waterfallAlignmentMinScrollOffset": Double(waterfallAlignmentScrollRange.lowerBound),
             "waterfallAlignmentMaxScrollOffset": Double(waterfallAlignmentScrollRange.upperBound),
-            "waterfallScrollable": waterfallAlignmentScrollable,
+            "waterfallScrollable": waterfallMaxScrollOffset > 0,
+            "waterfallAlignmentScrollable": waterfallAlignmentScrollable,
             "waterfallColumnCount": waterfallColumns.count,
             "waterfallColumnNames": waterfallColumns.map(\.column.app.name),
             "waterfallClipsToBounds": waterfallLayer.masksToBounds,
@@ -606,6 +1225,10 @@
             "waterfallAlignmentTolerance": Double(WaterfallAlignmentMetrics.tolerance),
             "waterfallAlignmentAnimationDurationMilliseconds": Double(WaterfallAlignmentMetrics.animationDuration * 1_000),
             "waterfallAlignmentAnimationTimingName": "easeOut",
+            "projectionTransitionMovedLayerCount": lastProjectionTransitionMovedLayerCount,
+            "projectionTransitionFadeInLayerCount": lastProjectionTransitionFadeInLayerCount,
+            "projectionTransitionFadeOutLayerCount": lastProjectionTransitionFadeOutLayerCount,
+            "projectionTransitionDurationMilliseconds": lastProjectionTransitionDurationMilliseconds,
             "reduceMotionEffective": NSWorkspace.shared.accessibilityDisplayShouldReduceMotion,
             "selectedAppGroupIndex": effectiveSelection?.appGroupIndex ?? NSNull(),
             "selectedWindowIndex": effectiveSelection?.windowIndex ?? NSNull(),
@@ -627,6 +1250,13 @@
             "closeConfirmationVisible": !closeConfirmationLayers.containerLayer.isHidden,
             "closeConfirmationFrame": dictionary(from: closeConfirmationLayers.containerLayer.frame),
             "closeConfirmationArrowEdge": closeConfirmationArrowEdge?.rawValue ?? NSNull(),
+            "closeFeedbackVisible": closeFeedback != nil && !closeFeedbackLayer.isHidden,
+            "closeFeedbackKind": closeFeedback?.kind.rawValue ?? NSNull(),
+            "closeFeedbackMessage": closeFeedback?.message ?? NSNull(),
+            "closeFeedbackTargetKind": closeFeedback?.targetKind ?? NSNull(),
+            "closeFeedbackAppGroupIndex": closeFeedback?.appGroupIndex ?? NSNull(),
+            "closeFeedbackWindowID": closeFeedback?.windowID ?? NSNull(),
+            "closeFeedbackFrame": dictionary(from: closeFeedbackLayer.frame),
             "mouseCommandsApplied": mouseCommandsApplied,
             "lastMouseCommand": lastMouseCommand ?? NSNull(),
             "lastClickedAppGroupIndex": lastClickedAppGroupIndex ?? NSNull(),
@@ -694,8 +1324,13 @@
             recordKeyboardCommand("enter")
             commitCurrentSelection()
         case "tab":
-            tabIgnoredCount += 1
-            recordKeyboardCommand("tabIgnored")
+            if isHorizontalMasonryMode {
+                recordKeyboardCommand("tab")
+                moveSelection(.right)
+            } else {
+                tabIgnoredCount += 1
+                recordKeyboardCommand("tabIgnored")
+            }
         default:
             recordKeyboardCommand("unknown:\(command)")
         }
@@ -756,7 +1391,7 @@
             }
             recordMouseCommand("hover-space:\(spaceID)")
             if let segment = spaceLaneSegment(spaceID: spaceID) {
-                hoverSpaceLaneSegment(segment)
+                hoverSpaceLaneSegment(segment, source: .debug)
             }
         case "click-space" where parts.count == 2:
             guard let spaceID = UInt64(parts[1]) else {
@@ -765,8 +1400,30 @@
             }
             recordMouseCommand("click-space:\(spaceID)")
             if let segment = spaceLaneSegment(spaceID: spaceID) {
-                clickSpaceLaneSegment(segment)
+                clickSpaceLaneSegment(segment, clickCount: 1)
             }
+        case "double-click-space" where parts.count == 2:
+            guard let spaceID = UInt64(parts[1]) else {
+                recordMouseCommand("invalid:\(command)")
+                return
+            }
+            recordMouseCommand("double-click-space:\(spaceID)")
+            if let segment = spaceLaneSegment(spaceID: spaceID) {
+                clickSpaceLaneSegment(segment, clickCount: 1)
+                clickSpaceLaneSegment(segment, clickCount: 2)
+            }
+        case "click-background":
+            recordMouseCommand("click-background")
+            _ = onBackgroundClick?()
+        case "hover-view-toggle":
+            recordMouseCommand("hover-view-toggle")
+            suppressViewModeToggleHoverPreview = false
+            isViewModeToggleButtonHovered = true
+            hoveredCloseTarget = nil
+            setHoverTarget(.none, source: .debug)
+        case "click-view-toggle", "click-settings":
+            recordMouseCommand("click-view-toggle")
+            clickViewModeToggleButton(source: "debug")
         case "hover-card" where parts.count == 3:
             guard let appGroupIndex = Int(parts[1]), let windowIndex = Int(parts[2]) else {
                 recordMouseCommand("invalid:\(command)")
@@ -774,7 +1431,7 @@
             }
             recordMouseCommand("hover-card:\(appGroupIndex):\(windowIndex)")
             if let card = waterfallCard(appGroupIndex: appGroupIndex, windowIndex: windowIndex) {
-                hoverWindowCard(card)
+                hoverWindowCard(card, source: .debug)
             }
         case "click-card" where parts.count == 3:
             guard let appGroupIndex = Int(parts[1]), let windowIndex = Int(parts[2]) else {
@@ -783,6 +1440,15 @@
             }
             recordMouseCommand("click-card:\(appGroupIndex):\(windowIndex)")
             if let card = waterfallCard(appGroupIndex: appGroupIndex, windowIndex: windowIndex) {
+                clickWindowCard(card)
+            }
+        case "click-card-id" where parts.count == 2:
+            guard let windowID = UInt32(parts[1]) else {
+                recordMouseCommand("invalid:\(command)")
+                return
+            }
+            recordMouseCommand("click-card-id:\(windowID)")
+            if let card = waterfallCard(windowID: windowID) {
                 clickWindowCard(card)
             }
         case "hover-card-close" where parts.count == 3:
@@ -826,13 +1492,12 @@
     }
 
     private func hoverAppGroup(_ appGroupIndex: Int) {
-        hoveredSpaceLaneID = nil
-        hoveredCloseTarget = nil
         updateHoverState(
             appGroupIndex: appGroupIndex,
             windowID: nil,
             spaceID: nil,
-            alignsWaterfallWithAppShelf: true
+            alignsWaterfallWithAppShelf: true,
+            source: .debug
         )
     }
 
@@ -847,19 +1512,18 @@
         beginCloseConfirmation(for: .app(appGroupIndex: appGroupIndex))
     }
 
-    private func hoverWindowCard(_ card: WaterfallCardLayers) {
-        hoveredSpaceLaneID = nil
-        hoveredCloseTarget = nil
+    private func hoverWindowCard(_ card: WaterfallCardLayers, source: HoverTargetSource = .event) {
         updateHoverState(
             appGroupIndex: card.item.appGroupIndex,
             windowID: card.item.window.id,
-            spaceID: card.item.primarySpaceID
+            spaceID: card.item.primarySpaceID,
+            source: source
         )
     }
 
     private func hoverCardCloseButton(appGroupIndex: Int, windowIndex: Int) {
         guard let card = waterfallCard(appGroupIndex: appGroupIndex, windowIndex: windowIndex) else { return }
-        hoverWindowCard(card)
+        hoverWindowCard(card, source: .debug)
         hoveredCloseTarget = .window(
             appGroupIndex: appGroupIndex,
             windowIndex: windowIndex,
@@ -880,33 +1544,23 @@
         )
     }
 
-    private func hoverSpaceLaneSegment(_ segment: SpaceLaneSegmentLayers) {
-        focusSpace(segment.space.id, persistent: false)
+    private func hoverSpaceLaneSegment(_ segment: SpaceLaneSegmentLayers, source: HoverTargetSource = .event) {
+        focusSpace(segment.space.id, persistent: false, source: source)
     }
 
-    private func clickSpaceLaneSegment(_ segment: SpaceLaneSegmentLayers) {
+    private func clickSpaceLaneSegment(_ segment: SpaceLaneSegmentLayers, clickCount: Int = 1) {
         DevelopmentDiagnostics.log("quickSwitch.view.clickSpaceLane", [
             "spaceID": segment.space.id,
-            "label": segment.space.label
+            "label": segment.space.label,
+            "clickCount": clickCount
         ])
         lastSpaceLaneClickSpaceID = segment.space.id
-
-        guard let firstCard = firstWaterfallCard(inSpaceID: segment.space.id) else {
-            DevelopmentDiagnostics.log("quickSwitch.view.clickSpaceLane.emptySpaceUnsupported", [
-                "spaceID": segment.space.id,
-                "label": segment.space.label
-            ])
-            return
-        }
-
-        commitWindowCard(firstCard, trigger: "spaceLane")
+        onSpaceLaneClick?(segment.space.id, clickCount)
+        lastSpaceLaneClickSpaceID = segment.space.id
     }
 
-    private func focusSpace(_ spaceID: UInt64, persistent: Bool) {
-        hoveredAppGroupIndex = nil
-        hoveredWindowID = nil
-        hoveredSpaceID = spaceID
-        hoveredSpaceLaneID = spaceID
+    private func focusSpace(_ spaceID: UInt64, persistent: Bool, source: HoverTargetSource = .event) {
+        setHoverTarget(.space(spaceID), source: source)
         if persistent {
             focusedSpaceID = spaceID
             lastSpaceLaneClickSpaceID = spaceID
@@ -1035,28 +1689,76 @@
         appGroupIndex: Int?,
         windowID: UInt32?,
         spaceID: UInt64?,
-        alignsWaterfallWithAppShelf: Bool = false
+        alignsWaterfallWithAppShelf: Bool = false,
+        source: HoverTargetSource = .event
     ) {
-        guard hoveredAppGroupIndex != appGroupIndex
-            || hoveredWindowID != windowID
-            || hoveredSpaceID != spaceID
-        else {
-            if alignsWaterfallWithAppShelf, let appGroupIndex {
-                alignWaterfallColumnWithAppShelfIcon(appGroupIndex: appGroupIndex, animated: true)
-            }
-            return
+        let target: HoverTarget
+        if let appGroupIndex, let windowID {
+            target = .window(appGroupIndex: appGroupIndex, windowID: windowID, spaceID: spaceID)
+        } else if let appGroupIndex {
+            target = .app(appGroupIndex)
+        } else {
+            target = .none
         }
 
-        hoveredAppGroupIndex = appGroupIndex
-        hoveredWindowID = windowID
-        hoveredSpaceID = spaceID
-        if alignsWaterfallWithAppShelf, let appGroupIndex {
+        setHoverTarget(target, source: source, alignsWaterfallWithAppShelf: alignsWaterfallWithAppShelf)
+    }
+
+    private func refreshHoverTarget(at windowLocation: CGPoint) {
+        guard debugHoveredAppGroupIndex == nil else { return }
+        let target = resolveHoverTarget(at: windowLocation)
+        setHoverTarget(target, alignsWaterfallWithAppShelf: target.shouldAlignWaterfallWithAppShelf)
+    }
+
+    private func resolveHoverTarget(at windowLocation: CGPoint) -> HoverTarget {
+        if let segment = spaceLaneSegment(at: windowLocation) {
+            return .space(segment.space.id)
+        }
+
+        if let card = waterfallCard(at: windowLocation) {
+            return .window(
+                appGroupIndex: card.item.appGroupIndex,
+                windowID: card.item.window.id,
+                spaceID: card.item.primarySpaceID
+            )
+        }
+
+        if let item = appShelfItem(at: windowLocation) {
+            return .app(item.item.appGroupIndex)
+        }
+
+        return .none
+    }
+
+    private func setHoverTarget(
+        _ target: HoverTarget,
+        source: HoverTargetSource = .event,
+        alignsWaterfallWithAppShelf: Bool = false
+    ) {
+        let previousTarget = hoverTarget
+        let previousSource = hoverTargetSource
+        hoverTarget = target
+        hoverTargetSource = source
+
+        hoveredAppGroupIndex = target.appGroupIndex
+        hoveredWindowID = target.windowID
+        hoveredSpaceID = target.spaceID
+        hoveredSpaceLaneID = target.spaceLaneID
+
+        if alignsWaterfallWithAppShelf, let appGroupIndex = target.appGroupIndex {
             alignWaterfallColumnWithAppShelfIcon(appGroupIndex: appGroupIndex, animated: true)
         }
+
+        guard previousTarget != target || previousSource != source else { return }
         needsLayout = true
     }
 
     private func moveSelection(_ direction: QuickSwitchKeyboardDirection) {
+        if isHorizontalMasonryMode {
+            moveHorizontalMasonrySelection(direction)
+            return
+        }
+
         guard let currentViewModel,
               let snapshot = snapshotForFocus(from: currentViewModel),
               let current = currentSelection ?? currentViewModel.initialSelection,
@@ -1086,6 +1788,113 @@
             "windowID": next.windowID
         ])
         needsLayout = true
+    }
+
+    private func moveHorizontalMasonrySelection(_ direction: QuickSwitchKeyboardDirection) {
+        guard let current = currentSelection ?? currentViewModel?.initialSelection,
+              let next = nextHorizontalMasonrySelection(from: current, direction: direction)
+        else {
+            DevelopmentDiagnostics.log("quickSwitch.view.moveHorizontalMasonrySelection.blocked", [
+                "direction": String(describing: direction),
+                "hasSelection": (currentSelection ?? currentViewModel?.initialSelection) != nil
+            ])
+            return
+        }
+
+        columnSelectionHistory[current.appGroupIndex] = current.windowIndex
+        currentSelection = next
+        columnSelectionHistory[next.appGroupIndex] = next.windowIndex
+        ensureCurrentSelectionVisible(horizontalIntent: .alignWithAppShelf(animated: true))
+        DevelopmentDiagnostics.log("quickSwitch.view.moveHorizontalMasonrySelection", [
+            "direction": String(describing: direction),
+            "appGroupIndex": next.appGroupIndex,
+            "windowIndex": next.windowIndex,
+            "windowID": next.windowID
+        ])
+        needsLayout = true
+    }
+
+    private func nextHorizontalMasonrySelection(
+        from current: QuickSwitchSelection,
+        direction: QuickSwitchKeyboardDirection
+    ) -> QuickSwitchSelection? {
+        layoutSubtreeIfNeeded()
+
+        let cards = horizontalMasonryCardsInPlacementOrder()
+        guard let currentIndex = cards.firstIndex(where: { $0.item.window.id == current.windowID }) else {
+            return cards.first.map(selectionForCard)
+        }
+
+        switch direction {
+        case .right:
+            return selectionForCard(cards[(currentIndex + 1) % cards.count])
+        case .left:
+            return selectionForCard(cards[(currentIndex - 1 + cards.count) % cards.count])
+        case .up:
+            return nearestHorizontalMasonrySelection(from: cards[currentIndex], direction: .up)
+                ?? selectionForCard(cards.first ?? cards[currentIndex])
+        case .down:
+            return nearestHorizontalMasonrySelection(from: cards[currentIndex], direction: .down)
+                ?? selectionForCard(cards.last ?? cards[currentIndex])
+        }
+    }
+
+    private func nearestHorizontalMasonrySelection(
+        from currentCard: WaterfallCardLayers,
+        direction: QuickSwitchKeyboardDirection
+    ) -> QuickSwitchSelection? {
+        let currentFrame = currentCard.containerLayer.frame
+        let candidates = horizontalMasonryCardsInPlacementOrder().filter { card in
+            guard card.item.window.id != currentCard.item.window.id else { return false }
+            switch direction {
+            case .up:
+                return card.containerLayer.frame.minY >= currentFrame.maxY - 0.5
+            case .down:
+                return card.containerLayer.frame.maxY <= currentFrame.minY + 0.5
+            case .left, .right:
+                return false
+            }
+        }
+
+        let best = candidates.min { lhs, rhs in
+            let lhsFrame = lhs.containerLayer.frame
+            let rhsFrame = rhs.containerLayer.frame
+            let lhsPrimaryDistance = direction == .up
+                ? lhsFrame.minY - currentFrame.maxY
+                : currentFrame.minY - lhsFrame.maxY
+            let rhsPrimaryDistance = direction == .up
+                ? rhsFrame.minY - currentFrame.maxY
+                : currentFrame.minY - rhsFrame.maxY
+            if abs(lhsPrimaryDistance - rhsPrimaryDistance) > 0.5 {
+                return lhsPrimaryDistance < rhsPrimaryDistance
+            }
+
+            let lhsHorizontalDistance = abs(lhsFrame.midX - currentFrame.midX)
+            let rhsHorizontalDistance = abs(rhsFrame.midX - currentFrame.midX)
+            if abs(lhsHorizontalDistance - rhsHorizontalDistance) > 0.5 {
+                return lhsHorizontalDistance < rhsHorizontalDistance
+            }
+
+            return lhs.item.globalIndex < rhs.item.globalIndex
+        }
+
+        return best.map(selectionForCard)
+    }
+
+    private func horizontalMasonryCardsInPlacementOrder() -> [WaterfallCardLayers] {
+        waterfallColumns
+            .sorted { $0.column.appGroupIndex < $1.column.appGroupIndex }
+            .flatMap { column in
+                column.cards.sorted { $0.item.windowIndex < $1.item.windowIndex }
+            }
+    }
+
+    private func selectionForCard(_ card: WaterfallCardLayers) -> QuickSwitchSelection {
+        QuickSwitchSelection(
+            appGroupIndex: card.item.appGroupIndex,
+            windowIndex: card.item.windowIndex,
+            windowID: card.item.window.id
+        )
     }
 
     private func commitCurrentSelection() {
@@ -1145,9 +1954,24 @@
         _ selection: QuickSwitchSelection,
         horizontalIntent: WaterfallHorizontalIntent = .reveal
     ) {
+        if isHorizontalMasonryMode {
+            switch horizontalIntent {
+            case .reveal:
+                ensureHorizontalMasonrySelectionVisible(selection, animated: false)
+            case .alignWithAppShelf(let animated):
+                ensureHorizontalMasonrySelectionVisible(selection, animated: animated)
+            }
+            return
+        }
+
         guard
             let column = waterfallColumns.first(where: { $0.column.appGroupIndex == selection.appGroupIndex })
         else {
+            return
+        }
+
+        if waterfallShouldKeepFilteredColumnsCentered {
+            ensureWaterfallCardVisibleVertically(selection)
             return
         }
 
@@ -1161,11 +1985,16 @@
     }
 
     private func ensureWaterfallCardVisibleVertically(_ selection: QuickSwitchSelection) {
+        guard !isHorizontalMasonryMode else {
+            ensureHorizontalMasonrySelectionVisible(selection, animated: false)
+            return
+        }
+
         let visibleHeight = max(
             1,
             waterfallLayer.bounds.height
                 - WaterfallMetrics.headerHeight
-                - WaterfallMetrics.columnPadding * 2
+                - WaterfallMetrics.columnVerticalPadding * 2
         )
         let cardStride = WaterfallMetrics.cardHeight + WaterfallMetrics.cardGap
         let cardStart = CGFloat(selection.windowIndex) * cardStride
@@ -1188,6 +2017,11 @@
     }
 
     private func alignWaterfallColumnWithAppShelfIcon(appGroupIndex: Int, animated: Bool) {
+        if isHorizontalMasonryMode {
+            ensureHorizontalMasonryAppVisible(appGroupIndex, animated: animated)
+            return
+        }
+
         guard
             let item = appShelfItems.first(where: { $0.item.appGroupIndex == appGroupIndex }),
             let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex })
@@ -1214,6 +2048,11 @@
     }
 
     private func ensureWaterfallColumnVisible(_ appGroupIndex: Int) {
+        if isHorizontalMasonryMode {
+            ensureHorizontalMasonryAppVisible(appGroupIndex, animated: false)
+            return
+        }
+
         guard let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex }) else {
             return
         }
@@ -1222,18 +2061,31 @@
     }
 
     private func ensureWaterfallColumnVisible(_ column: WaterfallColumnLayers) {
+        if isHorizontalMasonryMode {
+            ensureHorizontalMasonryAppVisible(column.column.appGroupIndex, animated: false)
+            return
+        }
+
         waterfallScrollOffset = clampedWaterfallOffset(
             scrollOffset(
                 makingVisible: column.containerLayer.frame,
                 currentOffset: waterfallScrollOffset,
                 visibleWidth: waterfallLayer.bounds.width,
                 maxOffset: waterfallMaxScrollOffset,
-                inset: WaterfallMetrics.revealPadding
+                inset: WaterfallMetrics.horizontalRevealPadding
             )
         )
     }
 
     private var waterfallAlignmentScrollRange: ClosedRange<CGFloat> {
+        if isHorizontalMasonryMode {
+            return 0...0
+        }
+
+        if waterfallShouldKeepFilteredColumnsCentered {
+            return 0...0
+        }
+
         var minimumOffset: CGFloat = 0
         var maximumOffset = waterfallMaxScrollOffset
 
@@ -1258,6 +2110,10 @@
     private func clampedWaterfallAlignmentOffset(_ offset: CGFloat) -> CGFloat {
         let range = waterfallAlignmentScrollRange
         return min(max(range.lowerBound, offset), range.upperBound)
+    }
+
+    private var waterfallShouldKeepFilteredColumnsCentered: Bool {
+        currentViewModel?.lockedSpaceID != nil && waterfallMaxScrollOffset <= 0.5
     }
 
     private func setWaterfallScrollOffset(_ offset: CGFloat, animated: Bool) {
@@ -1292,6 +2148,80 @@
         animation.timingFunction = CAMediaTimingFunction(name: WaterfallAlignmentMetrics.animationTimingName)
         animation.isRemovedOnCompletion = true
         waterfallContentLayer.add(animation, forKey: "waterfallColumnAlignment")
+    }
+
+    private func ensureHorizontalMasonrySelectionVisible(
+        _ selection: QuickSwitchSelection,
+        animated: Bool
+    ) {
+        guard let card = waterfallCard(
+            appGroupIndex: selection.appGroupIndex,
+            windowIndex: selection.windowIndex
+        ) else {
+            return
+        }
+
+        let visibleFrame = card.containerLayer.frame.offsetBy(
+            dx: 0,
+            dy: waterfallContentLayer.frame.minY
+        )
+        let visibleHeight = waterfallLayer.bounds.height
+        let padding = WaterfallMetrics.revealPadding
+        var nextOffset = horizontalMasonryScrollOffset
+
+        if visibleFrame.maxY > visibleHeight - padding {
+            nextOffset -= visibleFrame.maxY - (visibleHeight - padding)
+        } else if visibleFrame.minY < padding {
+            nextOffset += padding - visibleFrame.minY
+        }
+
+        setHorizontalMasonryScrollOffset(nextOffset, animated: animated)
+    }
+
+    private func ensureHorizontalMasonryAppVisible(_ appGroupIndex: Int, animated: Bool) {
+        guard let firstCard = waterfallColumns
+            .first(where: { $0.column.appGroupIndex == appGroupIndex })?
+            .cards
+            .sorted(by: { $0.item.windowIndex < $1.item.windowIndex })
+            .first
+        else {
+            return
+        }
+
+        let cardTopDistance = horizontalMasonryContentHeight - firstCard.containerLayer.frame.maxY
+        setHorizontalMasonryScrollOffset(
+            cardTopDistance - WaterfallMetrics.revealPadding,
+            animated: animated
+        )
+    }
+
+    private func setHorizontalMasonryScrollOffset(_ offset: CGFloat, animated: Bool) {
+        let nextOffset = clampedHorizontalMasonryOffset(offset)
+        let previousPositionY = waterfallContentLayer.presentation()?.position.y
+            ?? waterfallContentLayer.position.y
+
+        horizontalMasonryScrollOffset = nextOffset
+        CATransaction.begin()
+        CATransaction.setDisableActions(true)
+        waterfallContentLayer.frame = horizontalMasonryContentFrame()
+        CATransaction.commit()
+
+        let nextPositionY = waterfallContentLayer.position.y
+        guard animated,
+              !NSWorkspace.shared.accessibilityDisplayShouldReduceMotion,
+              abs(previousPositionY - nextPositionY) > 0.5
+        else {
+            waterfallContentLayer.removeAnimation(forKey: "horizontalMasonryAlignment")
+            return
+        }
+
+        let animation = CABasicAnimation(keyPath: "position.y")
+        animation.fromValue = previousPositionY
+        animation.toValue = nextPositionY
+        animation.duration = WaterfallAlignmentMetrics.animationDuration
+        animation.timingFunction = CAMediaTimingFunction(name: WaterfallAlignmentMetrics.animationTimingName)
+        animation.isRemovedOnCompletion = true
+        waterfallContentLayer.add(animation, forKey: "horizontalMasonryAlignment")
     }
 
     private func scrollOffset(
@@ -1408,8 +2338,8 @@
         glassLayer.shadowOpacity = 0
         rootLayer.addSublayer(glassLayer)
 
-        laneLayer.backgroundColor = NSColor.controlBackgroundColor.withAlphaComponent(0.68).cgColor
-        laneLayer.cornerRadius = 16
+        laneLayer.backgroundColor = NSColor.clear.cgColor
+        laneLayer.cornerRadius = 0
         laneLayer.masksToBounds = true
         glassLayer.addSublayer(laneLayer)
         laneLayer.addSublayer(spaceLaneContentLayer)
@@ -1427,6 +2357,34 @@
 
         closeConfirmationLayers.containerLayer.isHidden = true
         glassLayer.addSublayer(closeConfirmationLayers.containerLayer)
+
+        closeFeedbackLayer.isHidden = true
+        closeFeedbackLayer.opacity = 0
+        closeFeedbackLayer.cornerRadius = 11
+        closeFeedbackLayer.borderWidth = 1
+        closeFeedbackLayer.masksToBounds = false
+        closeFeedbackLayer.shadowColor = NSColor.black.cgColor
+        closeFeedbackLayer.shadowOpacity = 0.14
+        closeFeedbackLayer.shadowRadius = 16
+        closeFeedbackLayer.shadowOffset = CGSize(width: 0, height: -5)
+        closeFeedbackLayer.zPosition = 190
+        closeFeedbackTextLayer.contentsScale = backingScaleFactor
+        closeFeedbackTextLayer.font = NSFont.systemFont(ofSize: 13, weight: .medium)
+        closeFeedbackTextLayer.fontSize = 13
+        closeFeedbackTextLayer.alignmentMode = .center
+        closeFeedbackTextLayer.truncationMode = .end
+        closeFeedbackLayer.addSublayer(closeFeedbackTextLayer)
+        glassLayer.addSublayer(closeFeedbackLayer)
+
+        viewModeToggleButtonLayer.cornerRadius = 10
+        viewModeToggleButtonLayer.masksToBounds = false
+        viewModeToggleButtonLayer.borderWidth = 1
+        viewModeToggleButtonLayer.shadowColor = NSColor.black.cgColor
+        viewModeToggleButtonLayer.shadowOffset = CGSize(width: 0, height: -2)
+        viewModeToggleButtonLayer.zPosition = 170
+        viewModeToggleIconLayer.contentsScale = backingScaleFactor
+        viewModeToggleButtonLayer.addSublayer(viewModeToggleIconLayer)
+        glassLayer.addSublayer(viewModeToggleButtonLayer)
     }
 
     private func rebuildAppShelfItems() {
@@ -1434,22 +2392,15 @@
             item.containerLayer.removeFromSuperlayer()
         }
 
-        let selectedAppGroupIndex = effectiveSelection?.appGroupIndex
-        appShelfItems = (currentViewModel?.appShelf ?? []).map { item in
+        appShelfItems = (currentViewModel?.appShelf ?? []).enumerated().map { ordinal, item in
             let container = CALayer()
             container.name = item.app.name
 
             let background = CALayer()
             background.cornerRadius = 10
-            background.backgroundColor = (item.appGroupIndex == selectedAppGroupIndex
-                ? NSColor.systemFill.withAlphaComponent(0.16)
-                : NSColor.clear
-            ).cgColor
-            background.borderColor = (item.appGroupIndex == selectedAppGroupIndex
-                ? NSColor.separatorColor.withAlphaComponent(0.36)
-                : NSColor.clear
-            ).cgColor
-            background.borderWidth = item.appGroupIndex == selectedAppGroupIndex ? 1 : 0
+            background.backgroundColor = NSColor.clear.cgColor
+            background.borderColor = NSColor.clear.cgColor
+            background.borderWidth = 0
 
             let icon = CALayer()
             icon.contentsGravity = .resizeAspect
@@ -1457,6 +2408,18 @@
             icon.contents = appIconProvider.icon(for: item.app)
             icon.cornerRadius = 12
             icon.masksToBounds = false
+
+            let indexLabel = makeTextLayer(
+                string: appShelfIndexText(forOrdinal: ordinal),
+                fontSize: AppShelfMetrics.indexFontSize,
+                weight: .regular,
+                color: appShelfIndexColor,
+                alignment: .center
+            )
+            indexLabel.font = appShelfIndexFont(size: AppShelfMetrics.indexFontSize)
+            indexLabel.fontSize = AppShelfMetrics.indexFontSize
+            indexLabel.truncationMode = .end
+            indexLabel.zPosition = 14
 
             let label = makeTextLayer(
                 string: item.app.name,
@@ -1482,6 +2445,7 @@
             let closeButton = makeCloseButtonLayers()
 
             container.addSublayer(background)
+            container.addSublayer(indexLabel)
             container.addSublayer(icon)
             container.addSublayer(label)
             container.addSublayer(badge)
@@ -1492,6 +2456,7 @@
                 item: item,
                 containerLayer: container,
                 backgroundLayer: background,
+                indexLayer: indexLabel,
                 iconLayer: icon,
                 labelLayer: label,
                 badgeLayer: badge,
@@ -1523,7 +2488,8 @@
                 string: column.app.name,
                 fontSize: 13,
                 weight: .semibold,
-                color: .labelColor
+                color: .labelColor,
+                alignment: .center
             )
             let count = makeTextLayer(
                 string: "\(column.windows.count)",
@@ -1632,66 +2598,108 @@
     }
 
     private func rebuildSpaceLaneSegments() {
-        for segment in spaceLaneSegments {
-            segment.containerLayer.removeFromSuperlayer()
+        for group in spaceLaneDisplayGroups {
+            group.containerLayer.removeFromSuperlayer()
         }
 
-        let spaces = currentViewModel?.displays.flatMap(\.spaces) ?? []
-        spaceLaneSegments = spaces.map { space in
-            let container = CALayer()
-            container.name = space.label
-            container.cornerRadius = 10
-            container.borderWidth = 1
-            container.borderColor = NSColor.separatorColor.withAlphaComponent(0.34).cgColor
-            container.backgroundColor = spaceColor(for: space).cgColor
-            container.shadowColor = NSColor.black.cgColor
+        var groups: [SpaceLaneDisplayGroupLayers] = []
+        var allSegments: [SpaceLaneSegmentLayers] = []
 
-            let labelLayer = makeTextLayer(
-                string: space.label,
-                fontSize: 15,
-                weight: .semibold,
-                color: .labelColor
-            )
-            let countLayer = makeTextLayer(
-                string: "\(space.windowCount)",
-                fontSize: 12,
-                weight: .medium,
-                color: .secondaryLabelColor,
-                alignment: .center
-            )
-            let appLayer = makeTextLayer(
-                string: appIdentifierText(for: space),
-                fontSize: 12,
-                weight: space.type == .fullscreen ? .medium : .regular,
-                color: space.type == .fullscreen ? .labelColor : .secondaryLabelColor,
-                alignment: space.type == .fullscreen ? .center : .left
-            )
-            let windowBlocks = space.type == .fullscreen
-                ? []
-                : makeWindowBlocks(count: min(space.windowCount, 5), space: space)
-            let fullscreenMarkerLayer = makeFullscreenMarkerLayer(for: space)
+        for display in currentViewModel?.displays ?? [] {
+            let groupContainer = CALayer()
+            groupContainer.name = display.displayLabel
+            groupContainer.cornerRadius = 14
+            groupContainer.masksToBounds = false
+            groupContainer.borderWidth = 0
+            groupContainer.borderColor = NSColor.clear.cgColor
+            groupContainer.backgroundColor = NSColor.windowBackgroundColor.cgColor
+            groupContainer.shadowColor = NSColor.black.cgColor
+            groupContainer.shadowOpacity = 0
+            groupContainer.shadowRadius = 0
+            groupContainer.shadowOffset = .zero
 
-            container.addSublayer(labelLayer)
-            container.addSublayer(countLayer)
-            container.addSublayer(appLayer)
-            if let fullscreenMarkerLayer {
-                container.addSublayer(fullscreenMarkerLayer)
+            let segments = display.spaces.map { space in
+                let container = CAGradientLayer()
+                container.name = space.label
+                container.cornerRadius = 10
+                container.borderWidth = 1
+                container.borderColor = NSColor.separatorColor.withAlphaComponent(0.34).cgColor
+                container.backgroundColor = NSColor.clear.cgColor
+                container.startPoint = CGPoint(x: 0.5, y: 1.0)
+                container.endPoint = CGPoint(x: 0.5, y: 0.0)
+                container.shadowColor = NSColor.black.cgColor
+
+                let labelLayer = makeTextLayer(
+                    string: space.label,
+                    fontSize: 15,
+                    weight: .semibold,
+                    color: .labelColor
+                )
+                let countLayer = makeTextLayer(
+                    string: "\(space.windowCount)",
+                    fontSize: 12,
+                    weight: .medium,
+                    color: .secondaryLabelColor,
+                    alignment: .center
+                )
+                let appLayer = makeTextLayer(
+                    string: appIdentifierText(for: space),
+                    fontSize: 12,
+                    weight: space.type == .fullscreen ? .medium : .regular,
+                    color: space.type == .fullscreen ? .labelColor : .secondaryLabelColor,
+                    alignment: space.type == .fullscreen ? .center : .left
+                )
+                let splitAppLayers = splitViewAppNames(for: space).map { name in
+                    makeTextLayer(
+                        string: name,
+                        fontSize: 12,
+                        weight: .medium,
+                        color: .labelColor,
+                        alignment: .center
+                    )
+                }
+                let windowBlocks = space.type == .fullscreen
+                    ? []
+                    : makeWindowBlocks(count: min(space.windowCount, 5), space: space)
+                let fullscreenMarkerLayer = makeFullscreenMarkerLayer(for: space)
+
+                container.addSublayer(labelLayer)
+                container.addSublayer(countLayer)
+                container.addSublayer(appLayer)
+                if let fullscreenMarkerLayer {
+                    container.addSublayer(fullscreenMarkerLayer)
+                }
+                for splitAppLayer in splitAppLayers {
+                    container.addSublayer(splitAppLayer)
+                }
+                for block in windowBlocks {
+                    container.addSublayer(block)
+                }
+                groupContainer.addSublayer(container)
+
+                return SpaceLaneSegmentLayers(
+                    space: space,
+                    containerLayer: container,
+                    labelLayer: labelLayer,
+                    countLayer: countLayer,
+                    appLayer: appLayer,
+                    splitAppLayers: splitAppLayers,
+                    windowBlocks: windowBlocks,
+                    fullscreenMarkerLayer: fullscreenMarkerLayer
+                )
             }
-            for block in windowBlocks {
-                container.addSublayer(block)
-            }
-            spaceLaneContentLayer.addSublayer(container)
 
-            return SpaceLaneSegmentLayers(
-                space: space,
-                containerLayer: container,
-                labelLayer: labelLayer,
-                countLayer: countLayer,
-                appLayer: appLayer,
-                windowBlocks: windowBlocks,
-                fullscreenMarkerLayer: fullscreenMarkerLayer
-            )
+            spaceLaneContentLayer.addSublayer(groupContainer)
+            groups.append(SpaceLaneDisplayGroupLayers(
+                display: display,
+                containerLayer: groupContainer,
+                segments: segments
+            ))
+            allSegments.append(contentsOf: segments)
         }
+
+        spaceLaneDisplayGroups = groups
+        spaceLaneSegments = allSegments
     }
 
     private func layoutLayers() {
@@ -1740,8 +2748,161 @@
         layoutAppShelfItems()
         layoutWaterfallColumns()
         layoutCloseConfirmation()
+        layoutCloseFeedback()
+        layoutViewModeToggleButton()
 
         CATransaction.commit()
+    }
+
+    private func layoutViewModeToggleButton() {
+        let size = ViewModeToggleMetrics.visualSize
+        let topMargin = topSafeAreaInset + RootLayoutMetrics.topContentMargin
+        let x = max(
+            RootLayoutMetrics.horizontalMargin,
+            glassLayer.bounds.width - RootLayoutMetrics.horizontalMargin - size
+        )
+        let y = max(
+            RootLayoutMetrics.bottomMargin,
+            glassLayer.bounds.height - topMargin - size
+        )
+        viewModeToggleButtonLayer.frame = CGRect(x: x, y: y, width: size, height: size)
+        viewModeToggleButtonLayer.cornerRadius = ViewModeToggleMetrics.cornerRadius
+        let visualState = viewModeToggleVisualState
+        let isSelectedState = viewModeToggleVisualStateIsSelected(visualState)
+        viewModeToggleButtonLayer.backgroundColor = (isSelectedState
+            ? viewModeToggleBlueColor
+            : NSColor.windowBackgroundColor.withAlphaComponent(isViewModeToggleButtonHovered ? 0.76 : 0.58)
+        ).cgColor
+        viewModeToggleButtonLayer.borderColor = (isSelectedState
+            ? viewModeToggleBlueColor.withAlphaComponent(0.96)
+            : viewModeToggleBlueColor.withAlphaComponent(isViewModeToggleButtonHovered ? 0.72 : 0.34)
+        ).cgColor
+        viewModeToggleButtonLayer.shadowOpacity = isSelectedState ? 0.16 : (isViewModeToggleButtonHovered ? 0.11 : 0.06)
+        viewModeToggleButtonLayer.shadowRadius = isSelectedState
+            ? ViewModeToggleMetrics.selectedShadowRadius
+            : ViewModeToggleMetrics.idleShadowRadius
+        viewModeToggleIconLayer.contentsScale = backingScaleFactor
+        let iconInset = ViewModeToggleMetrics.iconInset
+        viewModeToggleIconLayer.frame = viewModeToggleButtonLayer.bounds.insetBy(dx: iconInset, dy: iconInset)
+        layoutViewModeToggleIcon()
+    }
+
+    private func layoutViewModeToggleIcon() {
+        CATransaction.begin()
+        CATransaction.setDisableActions(true)
+        viewModeToggleIconLayer.sublayers?.forEach { $0.removeFromSuperlayer() }
+
+        let bounds = viewModeToggleIconLayer.bounds
+        guard bounds.width > 0, bounds.height > 0 else {
+            CATransaction.commit()
+            return
+        }
+
+        let visualState = viewModeToggleVisualState
+        let isSelectedState = viewModeToggleVisualStateIsSelected(visualState)
+        let strokeColor = isSelectedState
+            ? NSColor.white.withAlphaComponent(0.98)
+            : viewModeToggleBlueColor.withAlphaComponent(0.96)
+        let fillColor = isSelectedState
+            ? NSColor.white.withAlphaComponent(0.22)
+            : viewModeToggleBlueColor.withAlphaComponent(0.06)
+        let glyphRect = centeredSquare(in: bounds)
+
+        switch visualState {
+        case .verticalAvailable, .verticalSelected:
+            addVerticalColumnsToggleGlyph(
+                in: glyphRect,
+                strokeColor: strokeColor,
+                fillColor: fillColor
+            )
+        case .horizontalAvailable, .horizontalSelected:
+            addHorizontalMasonryToggleGlyph(
+                in: glyphRect,
+                strokeColor: strokeColor,
+                fillColor: fillColor
+            )
+        }
+
+        CATransaction.commit()
+    }
+
+    private func addVerticalColumnsToggleGlyph(
+        in rect: CGRect,
+        strokeColor: NSColor,
+        fillColor: NSColor
+    ) {
+        let columnWidth = rect.width * 0.22
+        let gap = (rect.width - columnWidth * 3) / 2
+        for index in 0..<3 {
+            let x = rect.minX + CGFloat(index) * (columnWidth + gap)
+            let columnRect = CGRect(x: x, y: rect.minY, width: columnWidth, height: rect.height)
+            addViewModeToggleRoundedRect(
+                columnRect,
+                cornerRadius: ViewModeToggleMetrics.glyphCornerRadius,
+                strokeColor: strokeColor,
+                fillColor: fillColor,
+                lineWidth: ViewModeToggleMetrics.glyphLineWidth
+            )
+        }
+    }
+
+    private func addHorizontalMasonryToggleGlyph(
+        in rect: CGRect,
+        strokeColor: NSColor,
+        fillColor: NSColor
+    ) {
+        let cellSize = rect.width * 0.38
+        let gap = rect.width - cellSize * 2
+        for row in 0..<2 {
+            for column in 0..<2 {
+                let cellRect = CGRect(
+                    x: rect.minX + CGFloat(column) * (cellSize + gap),
+                    y: rect.minY + CGFloat(row) * (cellSize + gap),
+                    width: cellSize,
+                    height: cellSize
+                )
+                addViewModeToggleRoundedRect(
+                    cellRect,
+                    cornerRadius: ViewModeToggleMetrics.glyphCornerRadius,
+                    strokeColor: strokeColor,
+                    fillColor: fillColor,
+                    lineWidth: ViewModeToggleMetrics.glyphLineWidth
+                )
+            }
+        }
+    }
+
+    private func addViewModeToggleRoundedRect(
+        _ rect: CGRect,
+        cornerRadius: CGFloat,
+        strokeColor: NSColor,
+        fillColor: NSColor,
+        lineWidth: CGFloat
+    ) {
+        let layer = CAShapeLayer()
+        layer.contentsScale = backingScaleFactor
+        layer.frame = viewModeToggleIconLayer.bounds
+        layer.path = CGPath(
+            roundedRect: rect,
+            cornerWidth: cornerRadius,
+            cornerHeight: cornerRadius,
+            transform: nil
+        )
+        layer.fillColor = fillColor.cgColor
+        layer.strokeColor = strokeColor.cgColor
+        layer.lineWidth = lineWidth
+        layer.lineJoin = .round
+        viewModeToggleIconLayer.addSublayer(layer)
+    }
+
+    private func centeredSquare(in rect: CGRect) -> CGRect {
+        let side = min(rect.width, rect.height)
+        return CGRect(
+            x: rect.midX - side / 2,
+            y: rect.midY - side / 2,
+            width: side,
+            height: side
+        )
     }
 
     private var topSafeAreaInset: CGFloat {
@@ -1823,15 +2984,34 @@
     }
 
     private func layoutSpaceLaneSegments() {
-        guard !spaceLaneSegments.isEmpty else { return }
+        guard !spaceLaneDisplayGroups.isEmpty, !spaceLaneSegments.isEmpty else { return }
 
-        let gap: CGFloat = 10
-        let segmentHeight = max(1, laneLayer.bounds.height - 20)
-        let availableWidth = laneLayer.bounds.width - 24 - CGFloat(spaceLaneSegments.count - 1) * gap
-        let segmentWidth = max(96, min(150, availableWidth / CGFloat(spaceLaneSegments.count)))
+        let groupOuterVerticalInset: CGFloat = 6
+        let groupHeight = max(1, laneLayer.bounds.height - groupOuterVerticalInset * 2)
+        let segmentHeight = max(1, groupHeight - SpaceLaneMetrics.groupVerticalPadding * 2)
+        let groupGapWidth = CGFloat(max(0, spaceLaneDisplayGroups.count - 1)) * SpaceLaneMetrics.groupGap
+        let segmentGapWidth = spaceLaneDisplayGroups.reduce(CGFloat(0)) { total, group in
+            total + CGFloat(max(0, group.segments.count - 1)) * SpaceLaneMetrics.segmentGap
+        }
+        let groupPaddingWidth = CGFloat(spaceLaneDisplayGroups.count) * SpaceLaneMetrics.groupHorizontalPadding * 2
+        let availableWidth = laneLayer.bounds.width
+            - SpaceLaneMetrics.horizontalPadding * 2
+            - groupGapWidth
+            - segmentGapWidth
+            - groupPaddingWidth
+        let segmentWidth = max(
+            SpaceLaneMetrics.segmentMinWidth,
+            min(SpaceLaneMetrics.segmentMaxWidth, availableWidth / CGFloat(spaceLaneSegments.count))
+        )
+        let groupWidths = spaceLaneDisplayGroups.map { group in
+            SpaceLaneMetrics.groupHorizontalPadding * 2
+                + CGFloat(group.segments.count) * segmentWidth
+                + CGFloat(max(0, group.segments.count - 1)) * SpaceLaneMetrics.segmentGap
+        }
+        let segmentGroupWidth = groupWidths.reduce(0, +) + groupGapWidth
         spaceLaneContentWidth = max(
             laneLayer.bounds.width,
-            24 + CGFloat(spaceLaneSegments.count) * segmentWidth + CGFloat(spaceLaneSegments.count - 1) * gap
+            SpaceLaneMetrics.horizontalPadding * 2 + segmentGroupWidth
         )
         spaceLaneScrollOffset = clampedSpaceLaneOffset(spaceLaneScrollOffset)
         spaceLaneContentLayer.frame = CGRect(
@@ -1841,13 +3021,35 @@
             height: laneLayer.bounds.height
         )
 
-        var x: CGFloat = 12
+        var x = max(
+            SpaceLaneMetrics.horizontalPadding,
+            (spaceLaneContentWidth - segmentGroupWidth) / 2
+        )
 
-        for segment in spaceLaneSegments {
-            segment.containerLayer.frame = CGRect(x: x, y: 10, width: segmentWidth, height: segmentHeight)
-            applySpaceLaneVisualState(segment)
-            layoutSpaceLaneSegmentContents(segment)
-            x += segmentWidth + gap
+        for (index, group) in spaceLaneDisplayGroups.enumerated() {
+            let groupWidth = groupWidths[index]
+            group.containerLayer.frame = CGRect(
+                x: x,
+                y: groupOuterVerticalInset,
+                width: groupWidth,
+                height: groupHeight
+            )
+            applySpaceLaneDisplayGroupVisualState(group)
+
+            var segmentX = SpaceLaneMetrics.groupHorizontalPadding
+            for segment in group.segments {
+                segment.containerLayer.frame = CGRect(
+                    x: segmentX,
+                    y: SpaceLaneMetrics.groupVerticalPadding,
+                    width: segmentWidth,
+                    height: segmentHeight
+                )
+                applySpaceLaneVisualState(segment)
+                layoutSpaceLaneSegmentContents(segment)
+                segmentX += segmentWidth + SpaceLaneMetrics.segmentGap
+            }
+
+            x += groupWidth + SpaceLaneMetrics.groupGap
         }
     }
 
@@ -1859,36 +3061,127 @@
         min(max(0, offset), spaceLaneMaxScrollOffset)
     }
 
-    private func applySpaceLaneVisualState(_ segment: SpaceLaneSegmentLayers) {
-        let isHovered = segment.space.id == hoveredSpaceID
-        let isFocused = segment.space.id == activeSpaceFocusID
-        let isCurrent = segment.space.isCurrent
-        let isActive = isHovered || isFocused
+    private func applySpaceLaneDisplayGroupVisualState(_ group: SpaceLaneDisplayGroupLayers) {
+        let hasActiveSegment = group.segments.contains { segment in
+            segment.space.id == activeSpaceFocusID
+                || appHoverAssociatedSpaceIDs.contains(segment.space.id)
+                || segment.space.id == windowHoverAssociatedSpaceID
+                || segment.space.id == currentViewModel?.lockedSpaceID
+        }
+        let hasCurrentSegment = group.display.spaces.contains { $0.isCurrent }
+        group.containerLayer.backgroundColor = NSColor.windowBackgroundColor.cgColor
+        group.containerLayer.borderColor = NSColor.clear.cgColor
+        group.containerLayer.borderWidth = 0
+        group.containerLayer.shadowOpacity = 0
+        group.containerLayer.shadowRadius = 0
+        group.containerLayer.shadowOffset = .zero
+        group.containerLayer.zPosition = hasActiveSegment ? 8 : hasCurrentSegment ? 4 : 0
+        group.containerLayer.shadowPath = nil
+    }
 
-        segment.containerLayer.borderWidth = (isCurrent || isActive) ? 1.5 : 1
-        segment.containerLayer.borderColor = (isActive
-            ? NSColor.controlAccentColor.withAlphaComponent(0.54)
-            : isCurrent
-                ? NSColor.labelColor.withAlphaComponent(0.34)
+    private func applySpaceLaneVisualState(_ segment: SpaceLaneSegmentLayers) {
+        let isHovered = segment.space.id == activeSpaceFocusID
+        let isFocused = segment.space.id == activeSpaceFocusID
+        let isLocked = segment.space.id == currentViewModel?.lockedSpaceID
+        let isCurrent = segment.space.isCurrent
+        let hasWindows = segment.space.windowCount > 0
+        let isAppAssociated = appHoverAssociatedSpaceIDs.contains(segment.space.id)
+        let isWindowAssociated = segment.space.id == windowHoverAssociatedSpaceID
+        let isActive = isHovered || isFocused || isLocked
+        let isAssociated = (isAppAssociated || isWindowAssociated) && !isActive
+
+        segment.containerLayer.borderWidth = (hasWindows || isCurrent || isActive || isAssociated) ? 1.5 : 1
+        segment.containerLayer.borderColor = (isLocked
+            ? NSColor.white.withAlphaComponent(0.86)
+            : isActive
+            ? spaceLaneOccupiedColor.withAlphaComponent(isLocked ? 0.92 : 0.62)
+            : isAssociated
+                ? spaceLaneOccupiedColor.withAlphaComponent(0.50)
+                : hasWindows
+                    ? spaceLaneOccupiedColor.withAlphaComponent(isCurrent ? 0.54 : 0.44)
+                : isCurrent
+                    ? NSColor.labelColor.withAlphaComponent(0.34)
                 : NSColor.separatorColor.withAlphaComponent(0.34)
         ).cgColor
-        segment.containerLayer.backgroundColor = (isActive
-            ? accentTintedWindowBackground(fraction: 0.10, alpha: 0.94)
-            : spaceColor(for: segment.space)
-        ).cgColor
-        segment.containerLayer.shadowOpacity = isActive ? 0.26 : isCurrent ? 0.14 : 0
-        segment.containerLayer.shadowRadius = isActive ? 24 : isCurrent ? 12 : 0
-        segment.containerLayer.shadowOffset = CGSize(width: 0, height: isActive ? -6 : isCurrent ? -2.5 : 0)
-        segment.containerLayer.zPosition = isActive ? 30 : isCurrent ? 10 : 0
-        segment.containerLayer.transform = isActive
-            ? CATransform3DMakeScale(1.03, 1.03, 1)
-            : CATransform3DIdentity
-        segment.containerLayer.shadowPath = CGPath(
-            roundedRect: segment.containerLayer.bounds,
-            cornerWidth: segment.containerLayer.cornerRadius,
-            cornerHeight: segment.containerLayer.cornerRadius,
-            transform: nil
+        if isLocked {
+            applySpaceLaneSolidFill(
+                to: segment.containerLayer,
+                color: spaceLaneLockedFillColor
+            )
+        } else if !hasWindows {
+            applySpaceLaneSolidFill(to: segment.containerLayer, color: .clear)
+        } else if isActive {
+            applySpaceLaneSolidFill(
+                to: segment.containerLayer,
+                color: accentTintedWindowBackground(fraction: 0.10, alpha: 0.94)
+            )
+        } else if isAssociated {
+            applySpaceLaneSolidFill(
+                to: segment.containerLayer,
+                color: accentTintedWindowBackground(fraction: 0.07, alpha: 0.90)
+            )
+        } else if hasWindows {
+            applySpaceLaneGradientFill(
+                to: segment.containerLayer,
+                colors: spaceLaneIdleOccupiedGradientColors()
+            )
+        }
+        segment.containerLayer.shadowColor = isLocked
+            ? NSColor.white.withAlphaComponent(0.98).cgColor
+            : NSColor.black.cgColor
+        segment.containerLayer.shadowOpacity = (hasWindows || isLocked)
+            ? (isLocked ? 0.72 : isActive ? 0.26 : isAssociated ? 0.18 : isCurrent ? 0.14 : 0)
+            : 0
+        segment.containerLayer.shadowRadius = (hasWindows || isLocked)
+            ? (isLocked ? 30 : isActive ? 24 : isAssociated ? 18 : isCurrent ? 12 : 0)
+            : 0
+        segment.containerLayer.shadowOffset = CGSize(
+            width: 0,
+            height: (hasWindows || isLocked) ? (isLocked ? 0 : isActive ? -6 : isAssociated ? -4 : isCurrent ? -2.5 : 0) : 0
         )
+        segment.containerLayer.zPosition = isLocked ? 42 : isActive ? 30 : isAssociated ? 18 : isCurrent ? 10 : 0
+        segment.containerLayer.transform = (isActive || isAssociated)
+            ? CATransform3DMakeScale(isActive ? 1.03 : 1.015, isActive ? 1.03 : 1.015, 1)
+            : CATransform3DIdentity
+        segment.containerLayer.shadowPath = (hasWindows || isLocked)
+            ? CGPath(
+                roundedRect: segment.containerLayer.bounds,
+                cornerWidth: segment.containerLayer.cornerRadius,
+                cornerHeight: segment.containerLayer.cornerRadius,
+                transform: nil
+            )
+            : nil
+
+        applySpaceLaneContentVisualState(segment, isLocked: isLocked)
+    }
+
+    private func applySpaceLaneContentVisualState(_ segment: SpaceLaneSegmentLayers, isLocked: Bool) {
+        let primaryTextColor: NSColor = isLocked ? .white : .labelColor
+        let secondaryTextColor: NSColor = isLocked
+            ? .white
+            : .secondaryLabelColor
+
+        segment.labelLayer.foregroundColor = primaryTextColor.cgColor
+        segment.countLayer.foregroundColor = (isLocked ? NSColor.white : .secondaryLabelColor).cgColor
+        segment.appLayer.foregroundColor = (segment.space.type == .fullscreen
+            ? primaryTextColor
+            : secondaryTextColor
+        ).cgColor
+        for splitAppLayer in segment.splitAppLayers {
+            splitAppLayer.foregroundColor = primaryTextColor.cgColor
+        }
+
+        for block in segment.windowBlocks {
+            block.backgroundColor = (isLocked
+                ? NSColor.white
+                : spaceLaneOccupiedColor.withAlphaComponent(segment.space.isCurrent ? 0.72 : 0.58)
+            ).cgColor
+        }
+
+        (segment.fullscreenMarkerLayer as? CAShapeLayer)?.strokeColor = (isLocked
+            ? NSColor.white
+            : NSColor.secondaryLabelColor.withAlphaComponent(segment.space.isCurrent ? 0.42 : 0.28)
+        ).cgColor
     }
 
     private func shouldScrollSpaceLane(for event: NSEvent) -> Bool {
@@ -1944,13 +3237,48 @@
             y: locationInView.y - glassLayer.frame.minY - laneLayer.frame.minY - spaceLaneContentLayer.frame.minY
         )
 
-        return spaceLaneSegments.first { segment in
-            segment.containerLayer.frame.contains(locationInSpaceLaneContent)
+        for group in spaceLaneDisplayGroups where group.containerLayer.frame.contains(locationInSpaceLaneContent) {
+            let locationInGroup = CGPoint(
+                x: locationInSpaceLaneContent.x - group.containerLayer.frame.minX,
+                y: locationInSpaceLaneContent.y - group.containerLayer.frame.minY
+            )
+            if let segment = group.segments.first(where: { $0.containerLayer.frame.contains(locationInGroup) }) {
+                return segment
+            }
         }
+
+        return nil
     }
 
     private func spaceLaneSegment(spaceID: UInt64) -> SpaceLaneSegmentLayers? {
         spaceLaneSegments.first { $0.space.id == spaceID }
+    }
+
+    private func viewModeToggleButtonContains(windowLocation: CGPoint) -> Bool {
+        let locationInView = convert(windowLocation, from: nil)
+        let locationInGlass = CGPoint(
+            x: locationInView.x - glassLayer.frame.minX,
+            y: locationInView.y - glassLayer.frame.minY
+        )
+        let hitOutset = (ViewModeToggleMetrics.hitSize - ViewModeToggleMetrics.visualSize) / 2
+        return viewModeToggleButtonLayer.frame
+            .insetBy(dx: -hitOutset, dy: -hitOutset)
+            .contains(locationInGlass)
+    }
+
+    private func clickViewModeToggleButton(source: String) {
+        DevelopmentDiagnostics.log("quickSwitch.view.clickWaterfallViewModeToggle", [
+            "source": source,
+            "currentMode": waterfallViewMode.rawValue,
+            "targetMode": nextWaterfallViewMode.rawValue
+        ])
+        lastMouseCommand = "click-view-toggle"
+        if !mouseCommandsApplied.contains("click-view-toggle") {
+            mouseCommandsApplied.append("click-view-toggle")
+        }
+        isViewModeToggleButtonHovered = false
+        suppressViewModeToggleHoverPreview = true
+        onToggleWaterfallViewMode?()
     }
 
     private func appShelfItem(at windowLocation: CGPoint) -> AppShelfItemLayers? {
@@ -1992,23 +3320,61 @@
             .first(where: { $0.item.windowIndex == windowIndex })
     }
 
+    private func waterfallCard(windowID: UInt32) -> WaterfallCardLayers? {
+        waterfallColumns
+            .lazy
+            .flatMap(\.cards)
+            .first(where: { $0.item.window.id == windowID })
+    }
+
     private func layoutSpaceLaneSegmentContents(_ segment: SpaceLaneSegmentLayers) {
         let bounds = segment.containerLayer.bounds
+        let splitAppNames = splitViewAppNames(for: segment.space)
+        let isSplitView = splitAppNames.count >= 2
         segment.labelLayer.frame = CGRect(x: 10, y: bounds.height - 29, width: max(1, bounds.width - 48), height: 20)
         segment.countLayer.frame = CGRect(x: bounds.width - 34, y: bounds.height - 29, width: 24, height: 20)
+        segment.countLayer.string = isSplitView ? "" : "\(segment.space.windowCount)"
+        segment.countLayer.isHidden = isSplitView
         if segment.space.type == .fullscreen {
             let markerFrame = fullscreenMarkerFrame(in: bounds)
-            segment.appLayer.frame = CGRect(
-                x: 8,
-                y: markerFrame.midY - 8.5,
-                width: max(1, bounds.width - 16),
-                height: 17
-            )
+            segment.appLayer.isHidden = isSplitView
+            if isSplitView {
+                let labelY = markerFrame.midY - 8.5
+                let halfWidth = markerFrame.width / 2
+                for (index, splitAppLayer) in segment.splitAppLayers.enumerated() {
+                    let x = markerFrame.minX + CGFloat(index) * halfWidth
+                    splitAppLayer.isHidden = false
+                    splitAppLayer.frame = CGRect(
+                        x: x + 4,
+                        y: labelY,
+                        width: max(1, halfWidth - 8),
+                        height: 17
+                    )
+                }
+            } else {
+                segment.appLayer.frame = CGRect(
+                    x: 8,
+                    y: markerFrame.midY - 8.5,
+                    width: max(1, bounds.width - 16),
+                    height: 17
+                )
+                for splitAppLayer in segment.splitAppLayers {
+                    splitAppLayer.isHidden = true
+                }
+            }
         } else {
+            segment.appLayer.isHidden = false
             segment.appLayer.frame = CGRect(x: 10, y: 9, width: max(1, bounds.width - 20), height: 17)
+            for splitAppLayer in segment.splitAppLayers {
+                splitAppLayer.isHidden = true
+            }
         }
         if let fullscreenMarkerLayer = segment.fullscreenMarkerLayer {
-            layoutFullscreenMarkerLayer(fullscreenMarkerLayer, in: bounds)
+            layoutFullscreenMarkerLayer(
+                fullscreenMarkerLayer,
+                in: bounds,
+                isSplitView: isSplitView
+            )
         }
 
         let blockGap: CGFloat = 5
@@ -2069,8 +3435,8 @@
     private func layoutAppShelfItemContents(_ item: AppShelfItemLayers, iconSize: CGFloat) {
         let bounds = item.containerLayer.bounds
         let isSelected = item.item.appGroupIndex == effectiveSelection?.appGroupIndex
-        let showsSelectedVisual = shouldShowSelectedVisual(isSelected)
         let isHovered = item.item.appGroupIndex == effectiveHoveredAppGroupIndex
+        let showsSelectedVisual = shouldShowSelectedVisual(isSelected: isSelected, isHovered: isHovered)
         let isSpaceFocused = spaceFocusWindowCount(for: item.item.appGroupIndex) > 0
         let visualIconSize = appShelfVisualIconSize(
             forBaseIconSize: iconSize,
@@ -2124,6 +3490,13 @@
             )
             : nil
         item.iconLayer.frame = CGRect(x: iconX, y: iconY, width: visualIconSize, height: visualIconSize)
+        layoutAppShelfIndexLayer(
+            item.indexLayer,
+            iconFrame: item.iconLayer.frame,
+            iconSize: visualIconSize,
+            itemBounds: bounds,
+            highlighted: showsSelectedVisual || isHovered
+        )
         item.labelLayer.contentsScale = backingScaleFactor
         item.labelLayer.frame = CGRect(x: 0, y: 0, width: bounds.width, height: 14)
         item.badgeLayer.string = badgeText
@@ -2151,6 +3524,67 @@
         item.selectedIndicatorLayer.backgroundColor = NSColor.clear.cgColor
     }
 
+    private var appShelfIndexColor: NSColor {
+        NSColor.labelColor.withAlphaComponent(0.34)
+    }
+
+    private var appShelfIndexHighlightedColor: NSColor {
+        NSColor.labelColor.withAlphaComponent(0.42)
+    }
+
+    private func appShelfIndexFont(size: CGFloat) -> NSFont {
+        for fontName in ["Bradley Hand ITC", "Noteworthy-Light", "Marker Felt", "Snell Roundhand"] {
+            if let font = NSFont(name: fontName, size: size) {
+                return font
+            }
+        }
+
+        return NSFont.monospacedSystemFont(ofSize: size, weight: .regular)
+    }
+
+    private func appShelfIndexText(forOrdinal ordinal: Int) -> String {
+        let symbols = Array("1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ")
+        guard ordinal >= 0 else { return "" }
+        if ordinal < symbols.count {
+            return String(symbols[ordinal])
+        }
+
+        let overflowIndex = ordinal - symbols.count
+        let prefix = symbols[10 + (overflowIndex / 26) % 26]
+        let suffix = symbols[10 + overflowIndex % 26]
+        return "\(prefix)\(suffix)"
+    }
+
+    private func layoutAppShelfIndexLayer(
+        _ layer: CATextLayer,
+        iconFrame: CGRect,
+        iconSize: CGFloat,
+        itemBounds: CGRect,
+        highlighted: Bool
+    ) {
+        let fontSize = iconSize <= AppShelfMetrics.minIconSize + 1
+            ? AppShelfMetrics.compressedIndexFontSize
+            : AppShelfMetrics.indexFontSize
+        layer.contentsScale = backingScaleFactor
+        layer.font = appShelfIndexFont(size: fontSize)
+        layer.fontSize = fontSize
+        layer.foregroundColor = (highlighted ? appShelfIndexHighlightedColor : appShelfIndexColor).cgColor
+        layer.opacity = iconSize <= AppShelfMetrics.minIconSize + 1 ? 0.72 : 0.82
+
+        let indexWidth = AppShelfMetrics.indexWidth
+        let indexHeight = AppShelfMetrics.indexHeight
+        let preferredX = iconFrame.minX - indexWidth - 1
+        let clampedX = max(-6, min(itemBounds.width - indexWidth, preferredX))
+        let preferredY = iconFrame.maxY - indexHeight + 4
+        let clampedY = max(0, min(itemBounds.height - indexHeight, preferredY))
+        layer.frame = CGRect(
+            x: clampedX,
+            y: clampedY,
+            width: indexWidth,
+            height: indexHeight
+        )
+    }
+
     private func appShelfRows() -> [[AppShelfItemLayers]] {
         guard appShelfLayout.rows > 1 else { return [appShelfItems] }
 
@@ -2174,15 +3608,60 @@
     }
 
     private var activeSpaceFocusID: UInt64? {
-        hoveredSpaceLaneID
+        guard case .space(let spaceID) = hoverTarget else { return nil }
+
+        if hoverTargetSource == .debug {
+            return spaceID
+        }
+
+        guard let window else { return nil }
+        let currentMouseLocation = window.mouseLocationOutsideOfEventStream
+        guard let segment = spaceLaneSegment(at: currentMouseLocation),
+              segment.space.id == spaceID
+        else {
+            return nil
+        }
+        return spaceID
+    }
+
+    private var appHoverAssociatedSpaceIDs: Set<UInt64> {
+        guard case .app(let appGroupIndex) = hoverTarget else { return [] }
+        return Set(
+            waterfallColumns
+                .first { $0.column.appGroupIndex == appGroupIndex }?
+                .cards
+                .compactMap(\.item.primarySpaceID) ?? []
+        )
+    }
+
+    private var appIconHoverLinkedAppGroupIndex: Int? {
+        if let debugHoveredAppGroupIndex {
+            return debugHoveredAppGroupIndex
+        }
+        guard case .app(let appGroupIndex) = hoverTarget else { return nil }
+        return appGroupIndex
+    }
+
+    private var appHoverAssociatedSpaceLabels: [String] {
+        guard !appHoverAssociatedSpaceIDs.isEmpty else { return [] }
+        return currentViewModel?.displays
+            .flatMap(\.spaces)
+            .filter { appHoverAssociatedSpaceIDs.contains($0.id) }
+            .map(\.label)
+            .sorted() ?? []
+    }
+
+    private var windowHoverAssociatedSpaceID: UInt64? {
+        guard case .window(_, _, let spaceID) = hoverTarget else { return nil }
+        return spaceID
     }
 
     private var isSpaceAssociationActive: Bool {
         activeSpaceFocusID != nil
     }
 
-    private func shouldShowSelectedVisual(_ isSelected: Bool) -> Bool {
-        isSelected && !isSpaceAssociationActive
+    private func shouldShowSelectedVisual(isSelected: Bool, isHovered: Bool) -> Bool {
+        isSelected && isHovered && !isSpaceAssociationActive
     }
 
     private func spaceFocusedAppGroupIndexes() -> [Int] {
@@ -2227,6 +3706,10 @@
               let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex })
         else {
             return "none"
+        }
+
+        guard !isHorizontalMasonryMode else {
+            return "visible"
         }
 
         let visibleMinX = waterfallScrollOffset
@@ -2311,17 +3794,24 @@
     }
 
     private func layoutWaterfallColumns() {
+        if isHorizontalMasonryMode {
+            layoutHorizontalMasonryWaterfall()
+            return
+        }
+
         guard !waterfallColumns.isEmpty else {
             waterfallContentWidth = waterfallLayer.bounds.width
             waterfallScrollOffset = 0
+            horizontalMasonryContentHeight = waterfallLayer.bounds.height
+            horizontalMasonryScrollOffset = 0
             waterfallContentLayer.frame = waterfallLayer.bounds
             return
         }
 
         let columnWidth = waterfallColumnWidth()
-        let totalWidth = WaterfallMetrics.columnPadding * 2
-            + CGFloat(waterfallColumns.count) * columnWidth
+        let columnsWidth = CGFloat(waterfallColumns.count) * columnWidth
             + CGFloat(max(0, waterfallColumns.count - 1)) * WaterfallMetrics.gap
+        let totalWidth = WaterfallMetrics.contentHorizontalPadding * 2 + columnsWidth
         waterfallContentWidth = max(waterfallLayer.bounds.width, totalWidth)
         waterfallScrollOffset = clampedWaterfallAlignmentOffset(waterfallScrollOffset)
         waterfallContentLayer.frame = CGRect(
@@ -2331,7 +3821,7 @@
             height: waterfallLayer.bounds.height
         )
 
-        var x = WaterfallMetrics.columnPadding
+        var x = waterfallColumnStartX(columnsWidth: columnsWidth)
         for column in waterfallColumns {
             column.containerLayer.frame = CGRect(
                 x: x,
@@ -2344,9 +3834,177 @@
         }
     }
 
+    private func layoutHorizontalMasonryWaterfall() {
+        guard !waterfallColumns.isEmpty else {
+            waterfallContentWidth = waterfallLayer.bounds.width
+            waterfallScrollOffset = 0
+            horizontalMasonryContentHeight = waterfallLayer.bounds.height
+            horizontalMasonryScrollOffset = 0
+            waterfallContentLayer.frame = waterfallLayer.bounds
+            return
+        }
+
+        let layout = horizontalMasonryLayout()
+        waterfallContentWidth = waterfallLayer.bounds.width
+        waterfallScrollOffset = 0
+        horizontalMasonryContentHeight = layout.contentHeight
+        horizontalMasonryScrollOffset = clampedHorizontalMasonryOffset(horizontalMasonryScrollOffset)
+        waterfallContentLayer.frame = horizontalMasonryContentFrame()
+
+        for column in waterfallColumns {
+            column.containerLayer.frame = CGRect(
+                x: 0,
+                y: 0,
+                width: waterfallContentWidth,
+                height: horizontalMasonryContentHeight
+            )
+            column.containerLayer.masksToBounds = false
+            column.containerLayer.backgroundColor = NSColor.clear.cgColor
+            column.containerLayer.borderColor = NSColor.clear.cgColor
+            column.containerLayer.borderWidth = 0
+            column.containerLayer.shadowOpacity = 0
+            column.containerLayer.shadowRadius = 0
+            column.containerLayer.shadowOffset = .zero
+            column.headerLayer.isHidden = true
+            column.appNameLayer.isHidden = true
+            column.countLayer.isHidden = true
+
+            for card in column.cards {
+                if let frame = layout.cardFramesByWindowID[card.item.window.id] {
+                    card.containerLayer.frame = frame
+                } else {
+                    card.containerLayer.frame = .zero
+                }
+                layoutWaterfallCard(card)
+            }
+        }
+    }
+
+    private struct HorizontalMasonryLayout {
+        let contentHeight: CGFloat
+        let cardFramesByWindowID: [UInt32: CGRect]
+    }
+
+    private func horizontalMasonryLayout() -> HorizontalMasonryLayout {
+        let cards = horizontalMasonryCardsInPlacementOrder()
+        guard !cards.isEmpty else {
+            return HorizontalMasonryLayout(
+                contentHeight: waterfallLayer.bounds.height,
+                cardFramesByWindowID: [:]
+            )
+        }
+
+        let viewportWidth = max(1, waterfallLayer.bounds.width)
+        let availableWidth = max(
+            HorizontalMasonryMetrics.cardMinWidth,
+            viewportWidth - HorizontalMasonryMetrics.horizontalPadding * 2
+        )
+        let maximumLaneCount = max(
+            1,
+            Int(
+                floor(
+                    (availableWidth + HorizontalMasonryMetrics.horizontalGap)
+                        / (HorizontalMasonryMetrics.cardMinWidth + HorizontalMasonryMetrics.horizontalGap)
+                )
+            )
+        )
+        let laneCount = min(maximumLaneCount, max(1, cards.count))
+        let fittingWidth = (
+            availableWidth - CGFloat(max(0, laneCount - 1)) * HorizontalMasonryMetrics.horizontalGap
+        ) / CGFloat(laneCount)
+        let cardWidth = floor(
+            min(
+                HorizontalMasonryMetrics.cardMaxWidth,
+                max(HorizontalMasonryMetrics.cardMinWidth, fittingWidth)
+            )
+        )
+        let usedWidth = CGFloat(laneCount) * cardWidth
+            + CGFloat(max(0, laneCount - 1)) * HorizontalMasonryMetrics.horizontalGap
+        let startX = max(
+            HorizontalMasonryMetrics.horizontalPadding,
+            (viewportWidth - usedWidth) / 2
+        )
+
+        var laneHeights = Array(repeating: CGFloat(0), count: laneCount)
+        var plannedFrames: [(windowID: UInt32, x: CGFloat, top: CGFloat, width: CGFloat, height: CGFloat)] = []
+
+        for card in cards {
+            let laneIndex = laneHeights.enumerated().min { lhs, rhs in
+                if abs(lhs.element - rhs.element) > 0.5 {
+                    return lhs.element < rhs.element
+                }
+                return lhs.offset < rhs.offset
+            }?.offset ?? 0
+            let cardHeight = HorizontalMasonryMetrics.cardHeight
+            let x = startX + CGFloat(laneIndex) * (cardWidth + HorizontalMasonryMetrics.horizontalGap)
+            let top = HorizontalMasonryMetrics.verticalPadding + laneHeights[laneIndex]
+            plannedFrames.append((
+                windowID: card.item.window.id,
+                x: x,
+                top: top,
+                width: cardWidth,
+                height: cardHeight
+            ))
+            laneHeights[laneIndex] += cardHeight + HorizontalMasonryMetrics.verticalGap
+        }
+
+        let tallestLane = laneHeights.max().map {
+            max(0, $0 - HorizontalMasonryMetrics.verticalGap)
+        } ?? 0
+        let contentHeight = max(
+            waterfallLayer.bounds.height,
+            HorizontalMasonryMetrics.verticalPadding * 2 + tallestLane
+        )
+        let frames = Dictionary(
+            uniqueKeysWithValues: plannedFrames.map { planned in
+                (
+                    planned.windowID,
+                    CGRect(
+                        x: planned.x,
+                        y: contentHeight - planned.top - planned.height,
+                        width: planned.width,
+                        height: planned.height
+                    )
+                )
+            }
+        )
+
+        return HorizontalMasonryLayout(contentHeight: contentHeight, cardFramesByWindowID: frames)
+    }
+
+    private func horizontalMasonryContentFrame() -> CGRect {
+        let contentHeight = max(waterfallLayer.bounds.height, horizontalMasonryContentHeight)
+        return CGRect(
+            x: 0,
+            y: waterfallLayer.bounds.height - contentHeight + horizontalMasonryScrollOffset,
+            width: waterfallLayer.bounds.width,
+            height: contentHeight
+        )
+    }
+
+    private func waterfallColumnStartX(columnsWidth: CGFloat) -> CGFloat {
+        guard currentViewModel?.lockedSpaceID != nil else {
+            return WaterfallMetrics.contentHorizontalPadding
+        }
+
+        let centeredStart = (waterfallContentWidth - columnsWidth) / 2
+        return max(WaterfallMetrics.contentHorizontalPadding, centeredStart)
+    }
+
     private func layoutWaterfallColumn(_ column: WaterfallColumnLayers) {
+        column.containerLayer.cornerRadius = 14
+        column.containerLayer.masksToBounds = true
+        column.containerLayer.backgroundColor = NSColor.controlBackgroundColor.withAlphaComponent(0.56).cgColor
+        column.containerLayer.shadowOpacity = 0
+        column.containerLayer.shadowRadius = 0
+        column.containerLayer.shadowOffset = .zero
+        column.headerLayer.isHidden = false
+        column.appNameLayer.isHidden = false
+        column.countLayer.isHidden = false
+
         let bounds = column.containerLayer.bounds
         let isSpaceFocused = spaceFocusWindowCount(for: column.column.appGroupIndex) > 0
+        let isHovered = column.column.appGroupIndex == effectiveHoveredAppGroupIndex
         column.containerLayer.borderColor = (isSpaceFocused
             ? NSColor.separatorColor.withAlphaComponent(0.38)
             : NSColor.separatorColor.withAlphaComponent(0.24)
@@ -2358,22 +4016,26 @@
             width: bounds.width,
             height: WaterfallMetrics.headerHeight
         )
-        column.headerLayer.backgroundColor = (isSpaceFocused
-            ? NSColor.systemFill.withAlphaComponent(0.10)
-            : NSColor.controlBackgroundColor.withAlphaComponent(0.52)
+        column.headerLayer.backgroundColor = (isHovered
+            ? viewModeToggleBlueColor
+            : (isSpaceFocused
+                ? NSColor.systemFill.withAlphaComponent(0.10)
+                : NSColor.controlBackgroundColor.withAlphaComponent(0.52))
         ).cgColor
         column.appNameLayer.frame = CGRect(
-            x: WaterfallMetrics.columnPadding,
+            x: WaterfallMetrics.columnHeaderTextInset,
             y: bounds.height - 24,
-            width: max(1, bounds.width - 64),
+            width: max(1, bounds.width - WaterfallMetrics.columnHeaderTextInset * 2),
             height: 16
         )
+        column.appNameLayer.foregroundColor = (isHovered ? NSColor.white : NSColor.labelColor).cgColor
         column.countLayer.frame = CGRect(
             x: bounds.width - 48,
             y: bounds.height - 24,
             width: 36,
             height: 16
         )
+        column.countLayer.foregroundColor = (isHovered ? NSColor.white : NSColor.secondaryLabelColor).cgColor
 
         let appGroupIndex = column.column.appGroupIndex
         let verticalOffset = clampedWaterfallColumnOffset(
@@ -2382,10 +4044,10 @@
         )
         waterfallColumnScrollOffsets[appGroupIndex] = verticalOffset
 
-        let cardWidth = max(1, bounds.width - WaterfallMetrics.columnPadding * 2)
+        let cardWidth = max(1, bounds.width - WaterfallMetrics.columnHorizontalPadding * 2)
         let firstCardTop = bounds.height
             - WaterfallMetrics.headerHeight
-            - WaterfallMetrics.columnPadding
+            - WaterfallMetrics.columnVerticalPadding
             + verticalOffset
 
         for card in column.cards {
@@ -2394,7 +4056,7 @@
                 - WaterfallMetrics.cardHeight
                 - CGFloat(cardIndex) * (WaterfallMetrics.cardHeight + WaterfallMetrics.cardGap)
             card.containerLayer.frame = CGRect(
-                x: WaterfallMetrics.columnPadding,
+                x: WaterfallMetrics.columnHorizontalPadding,
                 y: y,
                 width: cardWidth,
                 height: WaterfallMetrics.cardHeight
@@ -2407,9 +4069,16 @@
         let bounds = card.containerLayer.bounds
         let isSelected = card.item.window.id == effectiveSelection?.windowID
         let isHovered = card.item.window.id == hoveredWindowID
-        applyWaterfallCardVisualState(card, selected: shouldShowSelectedVisual(isSelected), hovered: isHovered)
+        let isAppLinked = isHorizontalMasonryMode
+            && card.item.appGroupIndex == appIconHoverLinkedAppGroupIndex
+        applyWaterfallCardVisualState(
+            card,
+            selected: shouldShowSelectedVisual(isSelected: isSelected, isHovered: isHovered),
+            hovered: isHovered,
+            appLinked: isAppLinked
+        )
 
-        let outerInset: CGFloat = 8
+        let outerInset: CGFloat = 0
         let titleBarHeight: CGFloat = 26
         let titleGap: CGFloat = 6
         let titleBarFrame = CGRect(
@@ -2469,12 +4138,19 @@
         )
     }
 
-    private func applyWaterfallCardVisualState(_ card: WaterfallCardLayers, selected: Bool, hovered: Bool) {
-        let isSpaceFocused = card.item.primarySpaceID == activeSpaceFocusID
+    private func applyWaterfallCardVisualState(
+        _ card: WaterfallCardLayers,
+        selected: Bool,
+        hovered: Bool,
+        appLinked: Bool
+    ) {
+        let isSpaceFocused = isWaterfallCardSpaceFocused(card)
         card.containerLayer.backgroundColor = (selected
             ? NSColor.windowBackgroundColor.withAlphaComponent(0.94)
             : hovered
                 ? accentTintedWindowBackground(fraction: 0.09, alpha: 0.95)
+                : appLinked
+                    ? accentTintedWindowBackground(fraction: 0.08, alpha: 0.93)
                 : isSpaceFocused
                     ? accentTintedWindowBackground(fraction: 0.10, alpha: 0.94)
                 : NSColor.windowBackgroundColor.withAlphaComponent(0.82)
@@ -2483,27 +4159,31 @@
             ? NSColor.controlAccentColor.withAlphaComponent(0.52)
             : hovered
                 ? NSColor.controlAccentColor.withAlphaComponent(0.44)
+                : appLinked
+                    ? NSColor.controlAccentColor.withAlphaComponent(0.38)
                 : isSpaceFocused
                     ? NSColor.controlAccentColor.withAlphaComponent(0.42)
                 : NSColor.separatorColor.withAlphaComponent(0.28)
         ).cgColor
-        card.containerLayer.borderWidth = (selected || hovered || isSpaceFocused) ? 1.5 : 1
+        card.containerLayer.borderWidth = (selected || hovered || appLinked || isSpaceFocused) ? 1.5 : 1
         card.containerLayer.shadowColor = NSColor.black.cgColor
-        card.containerLayer.shadowOpacity = selected ? 0.24 : hovered ? 0.14 : isSpaceFocused ? 0.20 : 0
-        card.containerLayer.shadowRadius = selected ? 22 : hovered ? 17 : isSpaceFocused ? 24 : 0
+        card.containerLayer.shadowOpacity = selected ? 0.24 : hovered ? 0.14 : appLinked ? 0.16 : isSpaceFocused ? 0.20 : 0
+        card.containerLayer.shadowRadius = selected ? 22 : hovered ? 17 : appLinked ? 18 : isSpaceFocused ? 24 : 0
         card.containerLayer.shadowOffset = selected
             ? CGSize(width: 0, height: -6)
             : hovered
                 ? CGSize(width: 0, height: -2.5)
+                : appLinked
+                    ? CGSize(width: 0, height: -3)
                 : isSpaceFocused
                     ? CGSize(width: 0, height: -5)
                     : .zero
-        card.containerLayer.zPosition = selected ? 20 : hovered ? 10 : isSpaceFocused ? 8 : 0
+        card.containerLayer.zPosition = selected ? 20 : hovered ? 12 : appLinked ? 10 : isSpaceFocused ? 8 : 0
         let focusedScale: CGFloat = selected ? 1.015 : isSpaceFocused ? 1.012 : 1.008
         card.containerLayer.transform = (selected || hovered || isSpaceFocused)
             ? CATransform3DMakeScale(focusedScale, focusedScale, 1)
             : CATransform3DIdentity
-        card.containerLayer.shadowPath = (selected || hovered || isSpaceFocused)
+        card.containerLayer.shadowPath = (selected || hovered || appLinked || isSpaceFocused)
             ? CGPath(
                 roundedRect: card.containerLayer.bounds,
                 cornerWidth: card.containerLayer.cornerRadius,
@@ -2511,7 +4191,9 @@
                 transform: nil
             )
             : nil
-        card.titleBarLayer.backgroundColor = NSColor.clear.cgColor
+        card.titleBarLayer.backgroundColor = appLinked
+            ? spaceLaneOccupiedColor.withAlphaComponent(0.18).cgColor
+            : NSColor.clear.cgColor
         card.titleBarLayer.borderColor = NSColor.clear.cgColor
         card.titleBarLayer.borderWidth = 0
         card.shineLayer.opacity = selected ? 1 : 0
@@ -2527,13 +4209,14 @@
         let size: CGFloat = isButtonHovered ? 24 : 18
         let buttonFill = isButtonHovered
             ? NSColor.systemRed.withAlphaComponent(0.94)
-            : NSColor.labelColor.withAlphaComponent(0.24)
+            : NSColor.white.withAlphaComponent(0.34)
         let buttonStroke = isButtonHovered
             ? NSColor.white.withAlphaComponent(0.76)
-            : NSColor.white.withAlphaComponent(0.52)
+            : NSColor.white.withAlphaComponent(0.46)
         let glyphStroke = isButtonHovered
             ? NSColor.white
-            : NSColor.secondaryLabelColor.withAlphaComponent(0.92)
+            : NSColor.white.withAlphaComponent(0.88)
+
         button.containerLayer.frame = CGRect(
             x: anchorTopRight.x - size / 2,
             y: anchorTopRight.y - size / 2,
@@ -2545,10 +4228,10 @@
         button.containerLayer.borderColor = buttonStroke.cgColor
         button.containerLayer.opacity = visible ? 1 : 0
         button.containerLayer.zPosition = isButtonHovered ? 80 : 60
-        button.containerLayer.shadowOpacity = visible ? (isButtonHovered ? 0.22 : 0.07) : 0
+        button.containerLayer.shadowOpacity = visible ? (isButtonHovered ? 0.22 : 0.04) : 0
         button.containerLayer.shadowRadius = isButtonHovered ? 9 : 5
         button.glyphLayer.frame = CGRect(x: 0, y: 0, width: size, height: size)
-        button.glyphLayer.lineWidth = isButtonHovered ? 2.1 : 1.7
+        button.glyphLayer.lineWidth = isButtonHovered ? 2.1 : 1.45
         button.glyphLayer.strokeColor = glyphStroke.cgColor
         button.glyphLayer.path = closeGlyphPath(size: size, hovered: isButtonHovered)
     }
@@ -2641,6 +4324,80 @@
         layers.confirmButtonTextLayer.frame = layers.confirmButtonLayer.bounds.insetBy(dx: 0, dy: 7)
     }
 
+    private func setCloseFeedback(_ feedback: CloseFeedback, autoHideAfter delay: TimeInterval?) {
+        closeFeedbackHideTask?.cancel()
+        closeFeedback = feedback
+        closeFeedbackLayer.isHidden = false
+        closeFeedbackLayer.opacity = 1
+        closeFeedbackTextLayer.string = feedback.message
+        switch feedback.kind {
+        case .progress:
+            closeFeedbackLayer.backgroundColor = NSColor.windowBackgroundColor.withAlphaComponent(0.94).cgColor
+            closeFeedbackLayer.borderColor = NSColor.separatorColor.withAlphaComponent(0.28).cgColor
+            closeFeedbackTextLayer.foregroundColor = NSColor.secondaryLabelColor.withAlphaComponent(0.96).cgColor
+        case .failure:
+            closeFeedbackLayer.backgroundColor = NSColor.systemRed.withAlphaComponent(0.10).cgColor
+            closeFeedbackLayer.borderColor = NSColor.systemRed.withAlphaComponent(0.32).cgColor
+            closeFeedbackTextLayer.foregroundColor = NSColor.systemRed.withAlphaComponent(0.95).cgColor
+        }
+        needsLayout = true
+
+        guard let delay else {
+            closeFeedbackHideTask = nil
+            return
+        }
+
+        closeFeedbackHideTask = Task { @MainActor [weak self] in
+            try? await Task.sleep(nanoseconds: UInt64(delay * 1_000_000_000))
+            guard !Task.isCancelled,
+                  let self,
+                  self.closeFeedback == feedback
+            else {
+                return
+            }
+            self.clearCloseFeedback()
+        }
+    }
+
+    private func layoutCloseFeedback() {
+        guard let feedback = closeFeedback else {
+            closeFeedbackLayer.isHidden = true
+            closeFeedbackLayer.opacity = 0
+            return
+        }
+
+        closeFeedbackLayer.isHidden = false
+        closeFeedbackLayer.opacity = 1
+        let font = NSFont.systemFont(
+            ofSize: 13,
+            weight: feedback.kind == .failure ? .medium : .regular
+        )
+        closeFeedbackTextLayer.font = font
+        closeFeedbackTextLayer.fontSize = 13
+        let textWidth = (feedback.message as NSString).size(
+            withAttributes: [.font: font]
+        ).width
+        let maxWidth = max(180, glassLayer.bounds.width - 48)
+        let width = min(max(180, textWidth + 34), min(460, maxWidth))
+        let height: CGFloat = 34
+        let x = max(24, (glassLayer.bounds.width - width) / 2)
+        let preferredY = waterfallLayer.frame.maxY - height - 14
+        let y = min(
+            max(16, preferredY),
+            max(16, glassLayer.bounds.height - height - 16)
+        )
+
+        closeFeedbackLayer.frame = CGRect(x: x, y: y, width: width, height: height)
+        closeFeedbackLayer.cornerRadius = height / 2
+        closeFeedbackLayer.shadowPath = CGPath(
+            roundedRect: closeFeedbackLayer.bounds,
+            cornerWidth: closeFeedbackLayer.cornerRadius,
+            cornerHeight: closeFeedbackLayer.cornerRadius,
+            transform: nil
+        )
+        closeFeedbackTextLayer.frame = closeFeedbackLayer.bounds.insetBy(dx: 17, dy: 8)
+    }
+
     private func closeConfirmationBubblePath(
         bounds: CGRect,
         contentFrame: CGRect,
@@ -2726,18 +4483,23 @@
         }
 
         pendingCloseTarget = nil
+        pendingCloseRequest = nil
         pendingCloseOptOut = false
         closeConfirmationLayers.containerLayer.isHidden = true
         closeConfirmationArrowEdge = nil
-        if pendingCloseOptOut {
-            onCloseConfirmationDisabled?()
-        }
         onRequestClose?(request)
     }
 
     private func beginCloseConfirmation(for target: CloseTarget) {
         if closeConfirmationRequired {
+            guard let request = closeRequest(for: target) else {
+                DevelopmentDiagnostics.log("quickSwitch.view.closeConfirmation.missingRequest", [
+                    "targetKind": target.kindDescription
+                ])
+                return
+            }
             pendingCloseTarget = target
+            pendingCloseRequest = request
             pendingCloseOptOut = false
             DevelopmentDiagnostics.log("quickSwitch.view.closeConfirmation.show", [
                 "targetKind": target.kindDescription
@@ -2750,23 +4512,30 @@
     }
 
     private func confirmPendingClose() {
-        guard let target = pendingCloseTarget else { return }
+        guard let target = pendingCloseTarget,
+              let request = pendingCloseRequest
+        else { return }
         let shouldDisableConfirmation = pendingCloseOptOut
         pendingCloseTarget = nil
+        pendingCloseRequest = nil
         pendingCloseOptOut = false
         closeConfirmationLayers.containerLayer.isHidden = true
         closeConfirmationArrowEdge = nil
-        if shouldDisableConfirmation {
+        if shouldDisableConfirmation && closeConfirmationRequired {
+            closeConfirmationRequired = false
             onCloseConfirmationDisabled?()
         }
-        if let request = closeRequest(for: target) {
-            onRequestClose?(request)
-        }
+        DevelopmentDiagnostics.log("quickSwitch.view.closeConfirmation.confirm", [
+            "targetKind": target.kindDescription,
+            "disableFutureConfirmation": shouldDisableConfirmation
+        ])
+        onRequestClose?(request)
     }
 
     private func cancelPendingClose() {
         DevelopmentDiagnostics.log("quickSwitch.view.closeConfirmation.cancel")
         pendingCloseTarget = nil
+        pendingCloseRequest = nil
         pendingCloseOptOut = false
         closeConfirmationLayers.containerLayer.isHidden = true
         closeConfirmationArrowEdge = nil
@@ -2774,7 +4543,15 @@
     }
 
     private func toggleCloseConfirmationOptOut() {
+        if pendingCloseOptOut && !closeConfirmationRequired {
+            return
+        }
         pendingCloseOptOut.toggle()
+        if pendingCloseOptOut {
+            closeConfirmationRequired = false
+            onCloseConfirmationDisabled?()
+            DevelopmentDiagnostics.log("quickSwitch.view.closeConfirmation.optOutPersisted")
+        }
         needsLayout = true
     }
 
@@ -2941,13 +4718,18 @@
         return color.withAlphaComponent(alpha)
     }
 
+    private func isWaterfallCardSpaceFocused(_ card: WaterfallCardLayers) -> Bool {
+        guard let activeSpaceFocusID else { return false }
+        return card.item.primarySpaceID == activeSpaceFocusID
+    }
+
     private func waterfallColumnWidth() -> CGFloat {
         guard waterfallColumns.count > 0 else { return WaterfallMetrics.columnWidth }
 
         let visibleColumns = min(4, max(1, waterfallColumns.count))
         let fittingWidth = (
             waterfallLayer.bounds.width
-                - WaterfallMetrics.columnPadding * 2
+                - WaterfallMetrics.contentHorizontalPadding * 2
                 - CGFloat(max(0, visibleColumns - 1)) * WaterfallMetrics.gap
         ) / CGFloat(visibleColumns)
         return max(
@@ -2956,15 +4738,67 @@
         )
     }
 
+    private var isHorizontalMasonryMode: Bool {
+        waterfallViewMode == .horizontalMasonry
+    }
+
+    private var nextWaterfallViewMode: QuickSwitchWaterfallViewMode {
+        isHorizontalMasonryMode ? .verticalColumns : .horizontalMasonry
+    }
+
+    private var viewModeToggleBlueColor: NSColor {
+        NSColor(deviceRed: 135.0 / 255.0, green: 200.0 / 255.0, blue: 1, alpha: 1)
+    }
+
+    private var viewModeToggleVisualState: ViewModeToggleVisualState {
+        if isHorizontalMasonryMode {
+            return isViewModeToggleButtonHovered ? .verticalAvailable : .horizontalSelected
+        }
+        return isViewModeToggleButtonHovered ? .horizontalAvailable : .verticalSelected
+    }
+
+    private func viewModeToggleVisualStateIsSelected(_ state: ViewModeToggleVisualState) -> Bool {
+        switch state {
+        case .horizontalSelected, .verticalSelected:
+            return true
+        case .horizontalAvailable, .verticalAvailable:
+            return false
+        }
+    }
+
+    private var viewModeToggleIconKind: String {
+        viewModeToggleVisualState.rawValue
+    }
+
+    private var viewModeToggleAccessibilityLabel: String {
+        switch nextWaterfallViewMode {
+        case .verticalColumns:
+            return "切换到纵栏瀑布"
+        case .horizontalMasonry:
+            return "切换到横栏瀑布"
+        }
+    }
+
     private var waterfallMaxScrollOffset: CGFloat {
-        max(0, waterfallContentWidth - waterfallLayer.bounds.width)
+        guard !isHorizontalMasonryMode else { return 0 }
+        return max(0, waterfallContentWidth - waterfallLayer.bounds.width)
     }
 
     private func clampedWaterfallOffset(_ offset: CGFloat) -> CGFloat {
         min(max(0, offset), waterfallMaxScrollOffset)
     }
 
+    private var horizontalMasonryMaxScrollOffset: CGFloat {
+        max(0, horizontalMasonryContentHeight - waterfallLayer.bounds.height)
+    }
+
+    private func clampedHorizontalMasonryOffset(_ offset: CGFloat) -> CGFloat {
+        min(max(0, offset), horizontalMasonryMaxScrollOffset)
+    }
+
     private func waterfallMaxVerticalScrollOffset(for appGroupIndex: Int) -> CGFloat {
+        guard !isHorizontalMasonryMode else { return 0 }
+
         guard
             let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex })
         else {
@@ -2975,7 +4809,7 @@
             1,
             waterfallLayer.bounds.height
                 - WaterfallMetrics.headerHeight
-                - WaterfallMetrics.columnPadding * 2
+                - WaterfallMetrics.columnVerticalPadding * 2
         )
         let contentHeight = CGFloat(column.cards.count) * WaterfallMetrics.cardHeight
             + CGFloat(max(0, column.cards.count - 1)) * WaterfallMetrics.cardGap
@@ -3005,15 +4839,51 @@
         return states.joined(separator: " / ")
     }
 
-    private func spaceColor(for space: QuickSwitchSpaceViewModel) -> NSColor {
-        if space.isCurrent {
-            return NSColor.windowBackgroundColor.withAlphaComponent(0.76)
-        }
-        if space.windowCount > 0 {
-            return NSColor.controlBackgroundColor.withAlphaComponent(0.56)
+    private var spaceLaneOccupiedColor: NSColor {
+        if effectiveAppearance.bestMatch(from: [.darkAqua, .aqua]) == .darkAqua {
+            return NSColor(calibratedRed: 10 / 255, green: 132 / 255, blue: 1, alpha: 1)
         }
 
-        return NSColor.controlBackgroundColor.withAlphaComponent(0.26)
+        return NSColor(calibratedRed: 0, green: 122 / 255, blue: 1, alpha: 1)
+    }
+
+    private var spaceLaneLockedFillColor: NSColor {
+        if effectiveAppearance.bestMatch(from: [.darkAqua, .aqua]) == .darkAqua {
+            return NSColor(calibratedRed: 58 / 255, green: 148 / 255, blue: 1, alpha: 0.86)
+        }
+
+        return NSColor(calibratedRed: 90 / 255, green: 171 / 255, blue: 1, alpha: 0.82)
+    }
+
+    private func spaceLaneIdleOccupiedGradientColors() -> [NSColor] {
+        if effectiveAppearance.bestMatch(from: [.darkAqua, .aqua]) == .darkAqua {
+            let blue = NSColor(calibratedRed: 36 / 255, green: 54 / 255, blue: 72 / 255, alpha: 1)
+            let surface = NSColor.windowBackgroundColor.withAlphaComponent(1)
+            return [blue, surface]
+        }
+
+        return [
+            NSColor(calibratedRed: 232 / 255, green: 246 / 255, blue: 1, alpha: 1),
+            NSColor.white
+        ]
+    }
+
+    private func applySpaceLaneGradientFill(to layer: CALayer, colors: [NSColor]) {
+        if let gradientLayer = layer as? CAGradientLayer {
+            gradientLayer.colors = colors.map(\.cgColor)
+            gradientLayer.locations = [0, 1]
+            gradientLayer.startPoint = CGPoint(x: 0.5, y: 1.0)
+            gradientLayer.endPoint = CGPoint(x: 0.5, y: 0.0)
+        }
+        layer.backgroundColor = NSColor.clear.cgColor
+    }
+
+    private func applySpaceLaneSolidFill(to layer: CALayer, color: NSColor) {
+        if let gradientLayer = layer as? CAGradientLayer {
+            gradientLayer.colors = nil
+            gradientLayer.locations = nil
+        }
+        layer.backgroundColor = color.cgColor
     }
 
     private func makeFullscreenMarkerLayer(for space: QuickSwitchSpaceViewModel) -> CALayer? {
@@ -3179,10 +5049,9 @@
         return (0..<count).map { _ in
             let layer = CALayer()
             layer.cornerRadius = 3
-            layer.backgroundColor = (space.type == .fullscreen
-                ? NSColor.labelColor.withAlphaComponent(0.20)
-                : NSColor.labelColor.withAlphaComponent(0.18)
-            ).cgColor
+            layer.backgroundColor = spaceLaneOccupiedColor
+                .withAlphaComponent(space.isCurrent ? 0.72 : 0.58)
+                .cgColor
             return layer
         }
     }
@@ -3206,13 +5075,38 @@
         return identifiers.joined(separator: " ")
     }
 
-    private func layoutFullscreenMarkerLayer(_ layer: CALayer, in segmentBounds: CGRect) {
+    private func splitViewAppNames(for space: QuickSwitchSpaceViewModel) -> [String] {
+        guard space.type == .fullscreen else { return [] }
+
+        let names = space.splitViewAppNames
+            .prefix(2)
+            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
+            .filter { !$0.isEmpty }
+
+        guard names.count >= 2 else { return [] }
+        return names
+    }
+
+    private func layoutFullscreenMarkerLayer(
+        _ layer: CALayer,
+        in segmentBounds: CGRect,
+        isSplitView: Bool = false
+    ) {
         let markerFrame = fullscreenMarkerFrame(in: segmentBounds)
         layer.frame = markerFrame
 
         guard let shapeLayer = layer as? CAShapeLayer else { return }
 
         let bounds = shapeLayer.bounds
+        if isSplitView {
+            let path = CGMutablePath()
+            path.move(to: CGPoint(x: bounds.midX, y: bounds.minY))
+            path.addLine(to: CGPoint(x: bounds.midX, y: bounds.maxY))
+            shapeLayer.path = path
+            shapeLayer.lineCap = .butt
+            return
+        }
+
         let cornerLength = min(12, max(7, min(bounds.width, bounds.height) * 0.28))
         let path = CGMutablePath()
 
@@ -3233,14 +5127,22 @@
         path.addLine(to: CGPoint(x: 0, y: bounds.maxY - cornerLength))
 
         shapeLayer.path = path
+        shapeLayer.lineCap = .round
     }
 
     private func fullscreenMarkerFrame(in segmentBounds: CGRect) -> CGRect {
-        CGRect(
+        let topReserved: CGFloat = 32
+        let bottomReserved: CGFloat = 16
+        let availableHeight = max(20, segmentBounds.height - topReserved - bottomReserved)
+        let markerHeight = min(30, max(20, availableHeight))
+        let markerCenterY = bottomReserved + availableHeight * 0.5
+        let markerY = max(8, min(segmentBounds.height - topReserved - markerHeight, markerCenterY - markerHeight * 0.5))
+
+        return CGRect(
             x: 10,
-            y: 30,
+            y: markerY,
             width: max(1, segmentBounds.width - 20),
-            height: max(1, segmentBounds.height - 58)
+            height: markerHeight
         )
     }
 
@@ -3275,6 +5177,11 @@
                 "frame": dictionary(from: item.containerLayer.frame),
                 "visibleFrame": dictionary(from: visibleFrame),
                 "iconFrame": dictionary(from: item.iconLayer.frame),
+                "indexText": item.indexLayer.string ?? "",
+                "indexFrame": dictionary(from: item.indexLayer.frame),
+                "indexVisible": !item.indexLayer.isHidden && item.indexLayer.opacity > 0,
+                "indexFontSize": Double(item.indexLayer.fontSize),
+                "indexColor": colorDictionary(from: item.indexLayer.foregroundColor),
                 "labelFrame": dictionary(from: item.labelLayer.frame),
                 "labelTruncationMode": "middle",
                 "badgeVisible": !item.badgeLayer.isHidden,
@@ -3282,7 +5189,9 @@
                 "closeButtonVisible": item.closeButton.containerLayer.opacity > 0,
                 "closeButtonFrame": dictionary(from: item.closeButton.containerLayer.frame),
                 "closeButtonSize": Double(item.closeButton.containerLayer.bounds.width),
-                "closeButtonFillColor": colorDictionary(from: item.closeButton.containerLayer.backgroundColor)
+                "closeButtonFillColor": colorDictionary(from: item.closeButton.containerLayer.backgroundColor),
+                "closeButtonGlyphColor": colorDictionary(from: item.closeButton.glyphLayer.strokeColor),
+                "closeButtonGlyphLineWidth": Double(item.closeButton.glyphLayer.lineWidth)
             ] as [String: Any]
         }
     }
@@ -3290,12 +5199,13 @@
     private func appShelfVisualStates(for item: AppShelfItemLayers) -> [String] {
         var states: [String] = []
         let isSelected = item.item.appGroupIndex == effectiveSelection?.appGroupIndex
-        if shouldShowSelectedVisual(isSelected) {
+        let isHovered = item.item.appGroupIndex == effectiveHoveredAppGroupIndex
+        if shouldShowSelectedVisual(isSelected: isSelected, isHovered: isHovered) {
             states.append("selected")
         } else if isSelected {
             states.append("selectedVisualSuppressed")
         }
-        if item.item.appGroupIndex == effectiveHoveredAppGroupIndex {
+        if isHovered {
             states.append("hover")
         }
         if spaceFocusWindowCount(for: item.item.appGroupIndex) > 0 {
@@ -3308,21 +5218,51 @@
         return states
     }
 
+    private func waterfallColumnVisualStates(for column: WaterfallColumnLayers) -> [String] {
+        var states: [String] = []
+        if column.column.appGroupIndex == effectiveHoveredAppGroupIndex {
+            states.append("hover")
+        }
+        if spaceFocusWindowCount(for: column.column.appGroupIndex) > 0 {
+            states.append("spaceFocused")
+        }
+        return states
+    }
+
     private func waterfallColumnReports() -> [[String: Any]] {
         waterfallColumns.map { column in
             let visibleFrame = column.containerLayer.frame.offsetBy(dx: waterfallContentLayer.frame.minX, dy: 0)
             let appGroupIndex = column.column.appGroupIndex
+            let isHovered = appGroupIndex == effectiveHoveredAppGroupIndex
+            let firstCardFrame = column.cards.first?.containerLayer.frame
+            let headerToFirstCardGap = firstCardFrame.map {
+                column.headerLayer.frame.minY - $0.maxY
+            }
+            let topToFirstCardGap = firstCardFrame.map {
+                column.containerLayer.bounds.height - $0.maxY
+            }
 
             return [
                 "appGroupIndex": appGroupIndex,
                 "appName": column.column.app.name,
                 "bundleIdentifier": column.column.app.bundleIdentifier,
                 "windowCount": column.column.windows.count,
+                "isHovered": isHovered,
+                "visualStates": waterfallColumnVisualStates(for: column),
                 "spaceFocusWindowCount": spaceFocusWindowCount(for: appGroupIndex),
                 "isSpaceFocused": spaceFocusWindowCount(for: appGroupIndex) > 0,
                 "spaceFocusDirection": spaceFocusDirection(for: appGroupIndex),
                 "frame": dictionary(from: column.containerLayer.frame),
                 "visibleFrame": dictionary(from: visibleFrame),
+                "headerFrame": dictionary(from: column.headerLayer.frame),
+                "headerBackgroundColor": colorDictionary(from: column.headerLayer.backgroundColor),
+                "headerToFirstCardGap": headerToFirstCardGap.map(Double.init) ?? NSNull(),
+                "topToFirstCardGap": topToFirstCardGap.map(Double.init) ?? NSNull(),
+                "appNameFrame": dictionary(from: column.appNameLayer.frame),
+                "appNameAlignment": column.appNameLayer.alignmentMode.rawValue,
+                "appNameColor": colorDictionary(from: column.appNameLayer.foregroundColor),
+                "countFrame": dictionary(from: column.countLayer.frame),
+                "countColor": colorDictionary(from: column.countLayer.foregroundColor),
                 "verticalScrollOffset": Double(waterfallColumnScrollOffsets[appGroupIndex] ?? 0),
                 "maxVerticalScrollOffset": Double(waterfallMaxVerticalScrollOffset(for: appGroupIndex)),
                 "cards": waterfallCardReports(for: column)
@@ -3409,6 +5349,7 @@
                 "shadowRadius": Double(card.containerLayer.shadowRadius),
                 "thumbnailFrame": dictionary(from: card.thumbnailLayer.frame),
                 "titleBarFrame": dictionary(from: card.titleBarLayer.frame),
+                "titleBarBackgroundColor": colorDictionary(from: card.titleBarLayer.backgroundColor),
                 "titleBarBorderWidth": Double(card.titleBarLayer.borderWidth),
                 "titleFrame": dictionary(from: card.titleLayer.frame),
                 "metaFrame": dictionary(from: card.metaLayer.frame),
@@ -3418,6 +5359,8 @@
                 "closeButtonFrame": dictionary(from: card.closeButton.containerLayer.frame),
                 "closeButtonSize": Double(card.closeButton.containerLayer.bounds.width),
                 "closeButtonFillColor": colorDictionary(from: card.closeButton.containerLayer.backgroundColor),
+                "closeButtonGlyphColor": colorDictionary(from: card.closeButton.glyphLayer.strokeColor),
+                "closeButtonGlyphLineWidth": Double(card.closeButton.glyphLayer.lineWidth),
                 "shineVisible": card.shineLayer.opacity > 0,
                 "zPosition": Double(card.containerLayer.zPosition),
                 "frame": dictionary(from: card.containerLayer.frame),
@@ -3513,15 +5456,21 @@
     private func waterfallCardVisualStates(for card: WaterfallCardLayers) -> [String] {
         var states: [String] = []
         let isSelected = card.item.window.id == effectiveSelection?.windowID
-        if shouldShowSelectedVisual(isSelected) {
+        let isHovered = card.item.window.id == hoveredWindowID
+        let isAppLinked = isHorizontalMasonryMode
+            && card.item.appGroupIndex == appIconHoverLinkedAppGroupIndex
+        if shouldShowSelectedVisual(isSelected: isSelected, isHovered: isHovered) {
             states.append("selected")
         } else if isSelected {
             states.append("selectedVisualSuppressed")
         }
-        if card.item.window.id == hoveredWindowID {
+        if isHovered {
             states.append("hover")
         }
-        if card.item.primarySpaceID == activeSpaceFocusID {
+        if isAppLinked {
+            states.append("appLinked")
+        }
+        if isWaterfallCardSpaceFocused(card) {
             states.append("spaceFocused")
         }
         if card.item.window.isMinimized {
@@ -3537,32 +5486,105 @@
         window?.backingScaleFactor ?? NSScreen.main?.backingScaleFactor ?? 2
     }
 
+    private func spaceLaneDisplayGroupReports() -> [[String: Any]] {
+        spaceLaneDisplayGroups.map { group in
+            let visibleFrame = group.containerLayer.frame.offsetBy(dx: spaceLaneContentLayer.frame.minX, dy: 0)
+            return [
+                "displayUUID": group.display.displayUUID,
+                "displayIndex": group.display.displayIndex,
+                "displayLabel": group.display.displayLabel,
+                "physical": group.display.physical,
+                "spaceCount": group.segments.count,
+                "spaceIDs": group.segments.map(\.space.id),
+                "spaceLabels": group.segments.map(\.space.label),
+                "frame": dictionary(from: group.containerLayer.frame),
+                "visibleFrame": dictionary(from: visibleFrame),
+                "backgroundColor": colorDictionary(from: group.containerLayer.backgroundColor),
+                "borderColor": colorDictionary(from: group.containerLayer.borderColor),
+                "borderWidth": Double(group.containerLayer.borderWidth),
+                "shadowOpacity": Double(group.containerLayer.shadowOpacity),
+                "shadowRadius": Double(group.containerLayer.shadowRadius),
+                "groupGap": Double(SpaceLaneMetrics.groupGap),
+                "groupHorizontalPadding": Double(SpaceLaneMetrics.groupHorizontalPadding),
+                "groupVerticalPadding": Double(SpaceLaneMetrics.groupVerticalPadding),
+                "segmentGap": Double(SpaceLaneMetrics.segmentGap)
+            ] as [String: Any]
+        }
+    }
+
     private func spaceLaneSegmentReports() -> [[String: Any]] {
         currentViewModel?.displays.flatMap { display in
             display.spaces.compactMap { space in
                 guard let segment = spaceLaneSegments.first(where: { $0.space.id == space.id }) else {
                     return nil
                 }
-                let visibleFrame = segment.containerLayer.frame.offsetBy(dx: spaceLaneContentLayer.frame.minX, dy: 0)
+                let isAppAssociated = appHoverAssociatedSpaceIDs.contains(space.id)
+                let isWindowAssociated = space.id == windowHoverAssociatedSpaceID
+                let group = spaceLaneDisplayGroup(containingSpaceID: space.id)
+                let visibleFrame = segment.containerLayer.frame.offsetBy(
+                    dx: (group?.containerLayer.frame.minX ?? 0) + spaceLaneContentLayer.frame.minX,
+                    dy: group?.containerLayer.frame.minY ?? 0
+                )
+                let fullscreenMarkerFrame = segment.fullscreenMarkerLayer?.frame
+                let fullscreenMarkerCenterRatio = fullscreenMarkerFrame.map {
+                    Double($0.midY / max(1, segment.containerLayer.bounds.height))
+                }
+                let splitAppNames = splitViewAppNames(for: space)
+                let splitAppLabelFrames = segment.splitAppLayers.map { dictionary(from: $0.frame) }
                 return [
                     "displayUUID": display.displayUUID,
                     "displayLabel": display.displayLabel,
+                    "spaceID": space.id,
                     "label": space.label,
                     "type": spaceTypeName(space.type),
                     "visualStates": visualStates(for: space),
                     "fullscreenMarkerVisible": segment.fullscreenMarkerLayer != nil,
-                    "fullscreenMarkerKind": segment.fullscreenMarkerLayer == nil ? "none" : "cornerBracket",
-                    "fullscreenMarkerFrame": segment.fullscreenMarkerLayer.map { dictionary(from: $0.frame) } ?? NSNull(),
+                    "fullscreenMarkerKind": fullscreenMarkerKind(
+                        markerLayer: segment.fullscreenMarkerLayer,
+                        splitAppNames: splitAppNames
+                    ),
+                    "fullscreenMarkerPathStyle": fullscreenMarkerPathStyle(
+                        markerLayer: segment.fullscreenMarkerLayer,
+                        splitAppNames: splitAppNames
+                    ),
+                    "fullscreenMarkerFrame": fullscreenMarkerFrame.map { dictionary(from: $0) } ?? NSNull(),
+                    "fullscreenMarkerCenterRatio": fullscreenMarkerCenterRatio ?? NSNull(),
+                    "splitViewAppNames": splitAppNames,
+                    "splitViewLabelFrames": splitAppLabelFrames,
+                    "splitViewLabelColors": segment.splitAppLayers.map {
+                        colorDictionary(from: $0.foregroundColor)
+                    },
                     "windowBlockCount": segment.windowBlocks.count,
+                    "windowBlockColors": segment.windowBlocks.map { colorDictionary(from: $0.backgroundColor) },
+                    "windowBlockFrames": segment.windowBlocks.map { dictionary(from: $0.frame) },
+                    "labelColor": colorDictionary(from: segment.labelLayer.foregroundColor),
+                    "countText": string(from: segment.countLayer.string),
+                    "countVisible": !segment.countLayer.isHidden && segment.countLayer.opacity > 0,
+                    "countColor": colorDictionary(from: segment.countLayer.foregroundColor),
+                    "appColor": colorDictionary(from: segment.appLayer.foregroundColor),
+                    "fullscreenMarkerStrokeColor": colorDictionary(
+                        from: (segment.fullscreenMarkerLayer as? CAShapeLayer)?.strokeColor
+                    ),
+                    "backgroundKind": spaceLaneFillKind(for: segment.containerLayer),
                     "backgroundColor": colorDictionary(from: segment.containerLayer.backgroundColor),
+                    "gradientColors": gradientColorDictionaries(from: segment.containerLayer),
+                    "borderColor": colorDictionary(from: segment.containerLayer.borderColor),
+                    "borderWidth": Double(segment.containerLayer.borderWidth),
+                    "shadowColor": colorDictionary(from: segment.containerLayer.shadowColor),
                     "shadowOpacity": Double(segment.containerLayer.shadowOpacity),
                     "shadowRadius": Double(segment.containerLayer.shadowRadius),
+                    "shadowOffset": [
+                        "width": Double(segment.containerLayer.shadowOffset.width),
+                        "height": Double(segment.containerLayer.shadowOffset.height)
+                    ],
                     "appFrame": dictionary(from: segment.appLayer.frame),
                     "frame": dictionary(from: segment.containerLayer.frame),
                     "visibleFrame": dictionary(from: visibleFrame),
                     "isCurrent": space.isCurrent,
-                    "isHovered": space.id == hoveredSpaceID,
+                    "isHovered": space.id == activeSpaceFocusID,
                     "isFocused": space.id == activeSpaceFocusID,
+                    "isAppAssociated": isAppAssociated,
+                    "isWindowAssociated": isWindowAssociated,
                     "windowCount": space.windowCount,
                     "appCount": space.appCount,
                     "appNames": space.appNames
@@ -3571,19 +5593,47 @@
         } ?? []
     }
 
+    private func spaceLaneDisplayGroup(containingSpaceID spaceID: UInt64) -> SpaceLaneDisplayGroupLayers? {
+        spaceLaneDisplayGroups.first { group in
+            group.segments.contains { $0.space.id == spaceID }
+        }
+    }
+
+    private func fullscreenMarkerKind(markerLayer: CALayer?, splitAppNames: [String]) -> String {
+        guard markerLayer != nil else { return "none" }
+        return splitAppNames.count >= 2 ? "splitViewPair" : "cornerBracket"
+    }
+
+    private func fullscreenMarkerPathStyle(markerLayer: CALayer?, splitAppNames: [String]) -> String {
+        guard markerLayer != nil else { return "none" }
+        return splitAppNames.count >= 2 ? "centerDividerOnly" : "cornerBracket"
+    }
+
     private func visualStates(for space: QuickSwitchSpaceViewModel) -> [String] {
         var states: [String] = []
         if space.isCurrent {
             states.append("current")
         }
-        if space.id == hoveredSpaceID {
+        if appHoverAssociatedSpaceIDs.contains(space.id) {
+            states.append("appAssociated")
+        }
+        if space.id == windowHoverAssociatedSpaceID {
+            states.append("windowAssociated")
+        }
+        if space.id == activeSpaceFocusID {
             states.append("hover")
         }
         if space.id == activeSpaceFocusID {
             states.append("focused")
         }
+        if space.id == currentViewModel?.lockedSpaceID {
+            states.append("locked")
+        }
         if space.type == .fullscreen {
             states.append("fullscreen")
+        }
+        if splitViewAppNames(for: space).count >= 2 {
+            states.append("splitView")
         }
         return states
     }
@@ -3610,6 +5660,16 @@
         ]
     }
 
+    private func string(from textLayerValue: Any?) -> String {
+        if let string = textLayerValue as? String {
+            return string
+        }
+        if let attributedString = textLayerValue as? NSAttributedString {
+            return attributedString.string
+        }
+        return ""
+    }
+
     private func colorDictionary(from color: CGColor?) -> [String: Double] {
         guard let color,
               let nsColor = NSColor(cgColor: color)?.usingColorSpace(.deviceRGB)
@@ -3629,4 +5689,23 @@
             "alpha": Double(nsColor.alphaComponent)
         ]
     }
+
+    private func gradientColorDictionaries(from layer: CALayer) -> [[String: Double]] {
+        guard let gradientLayer = layer as? CAGradientLayer else { return [] }
+        return (gradientLayer.colors ?? []).map { color in
+            let cgColor = color as! CGColor
+            return colorDictionary(from: cgColor)
+        }
+    }
+
+    private func spaceLaneFillKind(for layer: CALayer) -> String {
+        if !gradientColorDictionaries(from: layer).isEmpty {
+            return "gradient"
+        }
+        let background = colorDictionary(from: layer.backgroundColor)
+        if background["alpha", default: 0] <= 0.01 {
+            return "clear"
+        }
+        return "solid"
+    }
 }

--
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