macos: transparent titlebar needs to be rehidden when tabs change

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

@@ -1,24 +1,39 @@
 import AppKit
 
 class TransparentTitlebarTerminalWindow: TerminalWindow {
-    private var debugTimer: Timer?
+    // We need to restore our last synced appearance so that we can reapply
+    // the appearance in certain scenarios.
+    private var lastSurfaceConfig: Ghostty.SurfaceView.DerivedConfig?
+    
+    // KVO observations
+    private var tabGroupWindowsObservation: NSKeyValueObservation?
 
     override func awakeFromNib() {
         super.awakeFromNib()
 
-        // Debug timer to print view hierarchy every second
-        debugTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] _ in
-            print("=== TransparentTitlebarTerminalWindow Debug ===")
-            self?.contentView?.rootView.printViewHierarchy()
-            print("===============================================\n")
-        }
+        // We need to observe the tab group because we need to redraw on
+        // tabbed window changes and there is no notification for that.
+        setupTabGroupObservation()
     }
     
     deinit {
-        debugTimer?.invalidate()
+        tabGroupWindowsObservation?.invalidate()
     }
 
+    override func becomeMain() {
+        // On macOS Tahoe, the tab bar redraws and restores non-transparency when
+        // switching tabs. To overcome this, we resync the appearance whenever this
+        // window becomes main (focused).
+        if #available(macOS 26.0, *),
+           let lastSurfaceConfig {
+            syncAppearance(lastSurfaceConfig)
+        }
+    }
+
+    // MARK: Appearance
+
     override func syncAppearance(_ surfaceConfig: Ghostty.SurfaceView.DerivedConfig) {
+        lastSurfaceConfig = surfaceConfig
         if #available(macOS 26.0, *) {
             syncAppearanceTahoe(surfaceConfig)
         } else {
@@ -47,6 +62,8 @@ class TransparentTitlebarTerminalWindow: TerminalWindow {
         titlebarContainer.layer?.backgroundColor = configBgColor.withAlphaComponent(surfaceConfig.backgroundOpacity).cgColor
     }
 
+    // MARK: View Finders
+
     private var titlebarBackgroundView: NSView? {
         titlebarContainer?.firstDescendant(withClassName: "NSTitlebarBackgroundView")
     }
@@ -76,4 +93,33 @@ class TransparentTitlebarTerminalWindow: TerminalWindow {
     private var titlebarContainerView: NSView? {
         contentView?.firstViewFromRoot(withClassName: "NSTitlebarContainerView")
     }
+    
+    // MARK: Tab Group Observation
+    
+    private func setupTabGroupObservation() {
+        // Remove existing observation if any
+        tabGroupWindowsObservation?.invalidate()
+        tabGroupWindowsObservation = nil
+        
+        // Check if tabGroup is available
+        guard let tabGroup else { return }
+
+        // Set up KVO observation for the windows array. Whenever it changes
+        // we resync the appearance because it can cause macOS to redraw the
+        // tab bar.
+        tabGroupWindowsObservation = tabGroup.observe(
+            \.windows,
+             options: [.new]
+        ) { [weak self] _, _ in
+            // NOTE: At one point, I guarded this on only if we went from 0 to N
+            // or N to 0 under the assumption that the tab bar would only get
+            // replaced on those cases. This turned out to be false (Tahoe).
+            // It's cheap enough to always redraw this so we should just do it
+            // unconditionally.
+
+            guard let self else { return }
+            guard let lastSurfaceConfig else { return }
+            self.syncAppearance(lastSurfaceConfig)
+        }
+    }
 }

macos/Sources/Helpers/Extensions/NSView+Extension.swift

@@ -118,6 +118,36 @@ extension NSView {
 		
 		// Add frame info
 		result += " [frame: \(frame)]"
+		
+		// Add visual properties
+		var properties: [String] = []
+		
+		// Hidden status
+		if isHidden {
+			properties.append("hidden")
+		}
+		
+		// Opaque status
+		properties.append(isOpaque ? "opaque" : "transparent")
+		
+		// Layer backing
+		if wantsLayer {
+			properties.append("layer-backed")
+			if let bgColor = layer?.backgroundColor {
+				let color = NSColor(cgColor: bgColor)
+				if let rgb = color?.usingColorSpace(.deviceRGB) {
+					properties.append(String(format: "bg:rgba(%.0f,%.0f,%.0f,%.2f)", 
+						rgb.redComponent * 255, 
+						rgb.greenComponent * 255, 
+						rgb.blueComponent * 255, 
+						rgb.alphaComponent))
+				} else {
+					properties.append("bg:\(bgColor)")
+				}
+			}
+		}
+		
+		result += " [\(properties.joined(separator: ", "))]"
 		result += "\n"
 		
 		// Process subviews