Portal: invalidate the split-divider hit-test cache on nested subview insertion

Sources/BrowserWindowPortal.swift

@@ -225,7 +225,7 @@ final class WindowBrowserHostView: NSView {
     private var cachedSidebarDividerX: CGFloat?
     private var sidebarDividerMissCount = 0
     private var cachedSplitDividerRegions: [DividerRegion]?
-    private var cachedSplitDividerRootSubviewIds: [ObjectIdentifier]?
+    private var cachedSplitDividerStructure: [PortalStructureSnapshot]?
     private let splitDividerCacheInvalidator = PortalSplitDividerCacheInvalidator()
     private var splitDividerResizeObserver: NSObjectProtocol?
     private var trackingArea: NSTrackingArea?
@@ -1033,12 +1033,11 @@ final class WindowBrowserHostView: NSView {
         return (pageFrame, inspectorFrame)
     }
     private func splitDividerRegions() -> [DividerRegion] {
-        guard let rootView = dividerSearchRootView() else { cachedSplitDividerRegions = []; cachedSplitDividerRootSubviewIds = nil; return [] }
-        let rootSubviewIds = rootView.subviews.map { ObjectIdentifier($0) }
-        if let regions = cachedSplitDividerRegions, cachedSplitDividerRootSubviewIds == rootSubviewIds, PortalSplitDividerRegion.allLive(regions) { return regions }
+        guard let rootView = dividerSearchRootView() else { cachedSplitDividerRegions = []; cachedSplitDividerStructure = nil; return [] }
+        if let regions = cachedSplitDividerRegions, let structure = cachedSplitDividerStructure, PortalSplitDividerRegion.structureSnapshotsMatch(structure), PortalSplitDividerRegion.allLive(regions) { return regions }
         let collected = PortalSplitDividerRegion.collect(in: rootView, hostView: self)
         cachedSplitDividerRegions = collected.regions
-        cachedSplitDividerRootSubviewIds = rootSubviewIds
+        cachedSplitDividerStructure = PortalSplitDividerRegion.structureSnapshots(of: collected.structureObservedViews)
         splitDividerCacheInvalidator.observe(
             geometryViews: collected.geometryObservedViews,
             structureViews: collected.structureObservedViews
@@ -1052,7 +1051,7 @@ final class WindowBrowserHostView: NSView {
 
     private func invalidateSplitDividerRegionCache() {
         cachedSplitDividerRegions = nil
-        cachedSplitDividerRootSubviewIds = nil
+        cachedSplitDividerStructure = nil
         splitDividerCacheInvalidator.invalidate()
     }
 

Sources/PortalSplitDividerRegion.swift

@@ -240,3 +240,32 @@ final class PortalSplitDividerRegion {
         }
     }
 }
+
+/// A snapshot of the subview-identity lists of the structure-observed views. Used to
+/// validate the split-divider cache without relying on KVO of `NSView.subviews`, which
+/// does not reliably fire for `addSubview(_:)` across macOS versions.
+struct PortalStructureSnapshot {
+    fileprivate weak var view: NSView?
+    fileprivate let subviewIds: [ObjectIdentifier]
+}
+
+extension PortalSplitDividerRegion {
+    static func structureSnapshots(of views: [NSView]) -> [PortalStructureSnapshot] {
+        views.map { PortalStructureSnapshot(view: $0, subviewIds: $0.subviews.map(ObjectIdentifier.init)) }
+    }
+
+    /// True only if every recorded view is still alive and its direct subview identities are
+    /// unchanged. A nested insertion changes an observed container's subview list, so this
+    /// catches it even when the KVO callback never fired.
+    static func structureSnapshotsMatch(_ snapshots: [PortalStructureSnapshot]) -> Bool {
+        for snapshot in snapshots {
+            guard let view = snapshot.view else { return false }
+            let subviews = view.subviews
+            guard subviews.count == snapshot.subviewIds.count,
+                  zip(subviews, snapshot.subviewIds).allSatisfy({ ObjectIdentifier($0.0) == $0.1 }) else {
+                return false
+            }
+        }
+        return true
+    }
+}

Sources/TerminalWindowPortal.swift

@@ -19,7 +19,7 @@ final class WindowTerminalHostView: NSView {
     private var cachedSidebarDividerX: CGFloat?
     private var sidebarDividerMissCount = 0
     private var cachedSplitDividerRegions: [DividerRegion]?
-    private var cachedSplitDividerRootSubviewIds: [ObjectIdentifier]?
+    private var cachedSplitDividerStructure: [PortalStructureSnapshot]?
     private let splitDividerCacheInvalidator = PortalSplitDividerCacheInvalidator()
     private var splitDividerResizeObserver: NSObjectProtocol?
     private var trackingArea: NSTrackingArea?
@@ -371,12 +371,11 @@ final class WindowTerminalHostView: NSView {
     }
 
     private func splitDividerRegions() -> [DividerRegion] {
-        guard let window, let rootView = window.contentView else { cachedSplitDividerRegions = []; cachedSplitDividerRootSubviewIds = nil; return [] }
-        let rootSubviewIds = rootView.subviews.map { ObjectIdentifier($0) }
-        if let regions = cachedSplitDividerRegions, cachedSplitDividerRootSubviewIds == rootSubviewIds, PortalSplitDividerRegion.allLive(regions) { return regions }
+        guard let window, let rootView = window.contentView else { cachedSplitDividerRegions = []; cachedSplitDividerStructure = nil; return [] }
+        if let regions = cachedSplitDividerRegions, let structure = cachedSplitDividerStructure, PortalSplitDividerRegion.structureSnapshotsMatch(structure), PortalSplitDividerRegion.allLive(regions) { return regions }
         let collected = PortalSplitDividerRegion.collect(in: rootView)
         cachedSplitDividerRegions = collected.regions
-        cachedSplitDividerRootSubviewIds = rootSubviewIds
+        cachedSplitDividerStructure = PortalSplitDividerRegion.structureSnapshots(of: collected.structureObservedViews)
         splitDividerCacheInvalidator.observe(
             geometryViews: collected.geometryObservedViews,
             structureViews: collected.structureObservedViews
@@ -390,7 +389,7 @@ final class WindowTerminalHostView: NSView {
 
     private func invalidateSplitDividerRegionCache() {
         cachedSplitDividerRegions = nil
-        cachedSplitDividerRootSubviewIds = nil
+        cachedSplitDividerStructure = nil
         splitDividerCacheInvalidator.invalidate()
     }