Fix `macos-titlebar-tabs` related issues (#9090)

### This pr fixes multiple issues related to `macos-titlebar-tabs`

- [Window title clipping **on
Tahoe**](https://github.com/ghostty-org/ghostty/discussions/9027#discussion-8981483)
- Clipped tab bar **on Tahoe** when creating new ones in fullscreen
> Sequoia doesn't seem to have this issue (at least I didn't reproduce
myself)
- [Title missing **on Tahoe** after dragging a tab into a separate
window](https://github.com/ghostty-org/ghostty/discussions/9027#discussioncomment-14617088)
- [Clipped tab bar **on Tahoe** after dragging from one tab group to
another](https://github.com/ghostty-org/ghostty/discussions/9027#discussioncomment-14626078)
- [Stretched tab bar after switching system
appearance](https://github.com/ghostty-org/ghostty/discussions/9027#discussioncomment-14626918)


### Related issues
I checked all of the open sub-issues in #2349 , most of them should be
fixed in latest main branch (I didn't reproduce)

- [#1692](https://github.com/ghostty-org/ghostty/issues/1692)
@peteschaffner
- [#1945](https://github.com/ghostty-org/ghostty/issues/1945) this one I
reproduce only on Tahoe, and fixed in this pr, @injust
- [#1813](https://github.com/ghostty-org/ghostty/issues/1813) @jacakira
- [#1787](https://github.com/ghostty-org/ghostty/issues/1787)
@roguesherlock
- [#1691](https://github.com/ghostty-org/ghostty/issues/1691) ~**haven't
found a solution yet**(building zig on VM is a pain**)~
> Tried commenting out `isOpaque` check in
`TitlebarTabsVenturaTerminalWindow`, which would fix the issue, but I
see the note there about transparency issue.
  >
> After commenting it out, it worked fine for me with blur and opacity
config, so **I might need some more background on this**. Didn't include
this change yet.
  > 
> [See screenshot
here](https://github.com/user-attachments/assets/eb17642d-b0de-46b2-b42a-19fb38a2c7f0)



### Minor improvements

- Match window title style with `window-title-font-family` and focus
state
  
<img width="843" height="198" alt="image"
src="https://github.com/user-attachments/assets/0138c4fa-1a4b-4bab-a415-b32695899ccf"
/>

---------

Co-authored-by: Mitchell Hashimoto <m@mitchellh.com>

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

@@ -19,9 +19,21 @@ class TitlebarTabsTahoeTerminalWindow: TransparentTitlebarTerminalWindow, NSTool
 
     // MARK: NSWindow
 
+    override var titlebarFont: NSFont? {
+        didSet {
+            DispatchQueue.main.async { [weak self] in
+                guard let self else { return }
+                self.viewModel.titleFont = self.titlebarFont
+            }
+        }
+    }
+
     override var title: String {
         didSet {
-            viewModel.title = title
+            DispatchQueue.main.async { [weak self] in
+                guard let self else { return }
+                self.viewModel.title = self.title
+            }
         }
     }
 
@@ -46,17 +58,33 @@ class TitlebarTabsTahoeTerminalWindow: TransparentTitlebarTerminalWindow, NSTool
         // Check if we have a tab bar and set it up if we have to. See the comment
         // on this function to learn why we need to check this here.
         setupTabBar()
+        
+        viewModel.isMainWindow = true
     }
 
+    override func resignMain() {
+        super.resignMain()
+        
+        viewModel.isMainWindow = false
+    }
     // This is called by macOS for native tabbing in order to add the tab bar. We hook into
     // this, detect the tab bar being added, and override its behavior.
     override func addTitlebarAccessoryViewController(_ childViewController: NSTitlebarAccessoryViewController) {
         // If this is the tab bar then we need to set it up for the titlebar
         guard isTabBar(childViewController) else {
+            // After dragging a tab into a new window, `hasTabBar` needs to be
+            // updated to properly review window title
+            viewModel.hasTabBar = false
+            
             super.addTitlebarAccessoryViewController(childViewController)
             return
         }
 
+        // When an existing tab is being dragged in to another tab group,
+        // system will also try to add tab bar to this window, so we want to reset observer,
+        // to put tab bar where we want again
+        tabBarObserver = nil
+        
         // Some setup needs to happen BEFORE it is added, such as layout. If
         // we don't do this before the call below, we'll trigger an AppKit
         // assertion.
@@ -116,18 +144,33 @@ class TitlebarTabsTahoeTerminalWindow: TransparentTitlebarTerminalWindow, NSTool
         guard tabBarObserver == nil else { return }
 
         // Find our tab bar. If it doesn't exist we don't do anything.
-        guard let tabBar = contentView?.rootView.firstDescendant(withClassName: "NSTabBar") else { return }
+        //
+        // In normal window, `NSTabBar` typically appears as a subview of `NSTitlebarView` within `NSThemeFrame`.
+        // In fullscreen, the system creates a dedicated fullscreen window and the view hierarchy changes;
+        // in that case, the `titlebarView` is only accessible via a reference on `NSThemeFrame`.
+        // ref: https://github.com/mozilla-firefox/firefox/blob/054e2b072785984455b3b59acad9444ba1eeffb4/widget/cocoa/nsCocoaWindow.mm#L7205
+        guard let themeFrameView = contentView?.rootView else { return }
+        let titlebarView = if themeFrameView.responds(to: Selector(("titlebarView"))) {
+            themeFrameView.value(forKey: "titlebarView") as? NSView
+        } else {
+            NSView?.none
+        }
+        guard let tabBar = titlebarView?.firstDescendant(withClassName: "NSTabBar") else { return }
 
         // View model updates must happen on their own ticks.
-        DispatchQueue.main.async {
+        DispatchQueue.main.async { [weak self] in
-            self.viewModel.hasTabBar = true
+            self?.viewModel.hasTabBar = true
         }
 
         // Find our clip view
         guard let clipView = tabBar.firstSuperview(withClassName: "NSTitlebarAccessoryClipView") else { return }
         guard let accessoryView = clipView.subviews[safe: 0] else { return }
-        guard let titlebarView = clipView.firstSuperview(withClassName: "NSTitlebarView") else { return }
+        guard let titlebarView else { return }
         guard let toolbarView = titlebarView.firstDescendant(withClassName: "NSToolbarView") else { return }
+        
+        // Make sure tabBar's height won't be stretched
+        guard let newTabButton = titlebarView.firstDescendant(withClassName: "NSTabBarNewTabButton") else { return }
+        tabBar.frame.size.height = newTabButton.frame.width
 
         // The container is the view that we'll constrain our tab bar within.
         let container = toolbarView
@@ -209,6 +252,8 @@ class TitlebarTabsTahoeTerminalWindow: TransparentTitlebarTerminalWindow, NSTool
         case .title:
             let item = NSToolbarItem(itemIdentifier: .title)
             item.view = NSHostingView(rootView: TitleItem(viewModel: viewModel))
+            // Fix: https://github.com/ghostty-org/ghostty/discussions/9027
+            item.view?.setContentCompressionResistancePriority(.required, for: .horizontal)
             item.visibilityPriority = .user
             item.isEnabled = true
 
@@ -225,8 +270,10 @@ class TitlebarTabsTahoeTerminalWindow: TransparentTitlebarTerminalWindow, NSTool
     // MARK: SwiftUI
 
     class ViewModel: ObservableObject {
+        @Published var titleFont: NSFont?
         @Published var title: String = "👻 Ghostty"
         @Published var hasTabBar: Bool = false
+        @Published var isMainWindow: Bool = true
     }
 }
 
@@ -249,15 +296,24 @@ extension TitlebarTabsTahoeTerminalWindow {
 
         var body: some View {
             if !viewModel.hasTabBar {
-                Text(title)
+                titleText
-                    .lineLimit(1)
-                    .truncationMode(.tail)
             } else {
                 // 1x1.gif strikes again! For real: if we render a zero-sized
                 // view here then the toolbar just disappears our view. I don't
-                // know.
+                // know. This appears fixed in 26.1 Beta but keep it safe for 26.0.
                 Color.clear.frame(width: 1, height: 1)
             }
         }
+        
+        @ViewBuilder
+        var titleText: some View {
+            Text(title)
+                .font(viewModel.titleFont.flatMap(Font.init(_:)))
+                .foregroundStyle(viewModel.isMainWindow ? .primary : .secondary)
+                .lineLimit(1)
+                .truncationMode(.tail)
+                .frame(maxWidth: .greatestFiniteMagnitude, alignment: .center)
+                .opacity(viewModel.hasTabBar ? 0 : 1) // hide when in fullscreen mode, where title bar will appear in the leading area under window buttons
+        }
     }
 }