macos: fix up some sequoia regressions

macos/Sources/Features/Terminal/Window Styles/TerminalWindow.swift

@@ -173,13 +173,7 @@ class TerminalWindow: NSWindow {
         return childViewController.identifier == Self.tabBarIdentifier
     }
 
-    /// Ensures we only run didAppear/didDisappear once per state.
-    private var tabBarDidAppearRan = false
-
     private func tabBarDidAppear() {
-        guard !tabBarDidAppearRan else { return }
-        tabBarDidAppearRan = true
-
         // Remove our reset zoom accessory. For some reason having a SwiftUI
         // titlebar accessory causes our content view scaling to be wrong.
         // Removing it fixes it, we just need to remember to add it again later.
@@ -189,11 +183,12 @@ class TerminalWindow: NSWindow {
     }
 
     private func tabBarDidDisappear() {
-        guard tabBarDidAppearRan else { return }
-        tabBarDidAppearRan = false
-
+        if styleMask.contains(.titled) {
+            if titlebarAccessoryViewControllers.firstIndex(of: resetZoomAccessory) == nil {
                 addTitlebarAccessoryViewController(resetZoomAccessory)
             }
+        }
+    }
 
     // MARK: Tab Key Equivalents
 
@@ -449,6 +444,16 @@ extension TerminalWindow {
         @ObservedObject var viewModel: ViewModel
         let action: () -> Void
         
+        // The padding from the top that the view appears. This was all just manually
+        // measured based on the OS.
+        var topPadding: CGFloat {
+            if #available(macOS 26.0, *) {
+                return viewModel.hasToolbar ? 10 : 5
+            } else {
+                return viewModel.hasToolbar ? 9 : 4
+            }
+        }
+
         var body: some View {
             if viewModel.isSurfaceZoomed {
                 VStack {
@@ -463,7 +468,7 @@ extension TerminalWindow {
                 }
                 // With a toolbar, the window title is taller, so we need more padding
                 // to properly align.
-                .padding(.top, viewModel.hasToolbar ? 10 : 5)
+                .padding(.top, topPadding)
                 // We always need space at the end of the titlebar
                 .padding(.trailing, 10)
             }

macos/Sources/Helpers/Fullscreen.swift

@@ -268,19 +268,15 @@ class NonNativeFullscreen: FullscreenBase, FullscreenStyle {
         // Removing the "titled" style also derefs all our accessory view controllers
         // so we need to restore those.
         for c in savedState.titlebarAccessoryViewControllers {
+            if window.titlebarAccessoryViewControllers.firstIndex(of: c) == nil {
                 window.addTitlebarAccessoryViewController(c)
             }
+        }
 
         // Removing "titled" also clears our toolbar
         window.toolbar = savedState.toolbar
         window.toolbarStyle = savedState.toolbarStyle
         
-        // This is a hack that I want to remove from this but for now, we need to
-        // fix up the titlebar tabs here before we do everything below.
-        if let window = window as? TitlebarTabsVenturaTerminalWindow, window.titlebarTabs {
-            window.titlebarTabs = true
-        }
-
         // If the window was previously in a tab group that isn't empty now,
         // we re-add it. We have to do this because our process of doing non-native
         // fullscreen removes the window from the tab group.