fix: prevent large-window glass corruption

src/bro_mac.mm

@@ -301,6 +301,7 @@ @interface BroWindow : NSWindow {
 @property (nonatomic, strong) BroToolbar* navToolbar;
 @property (nonatomic, strong) BroTabBar* tabBar;
 @property (nonatomic, strong) NSView* shellSurface;
+@property (nonatomic, strong) NSView* chromeSurface;
 @property (nonatomic, strong) NSView* borderOverlay;
 - (BOOL)glassBackdropVisible;
 - (void)setGlassBackdropVisible:(BOOL)visible;
@@ -346,22 +347,40 @@ - (instancetype)init {
     self.contentView = content;
     g_shell_corner_radius = BroResolveShellCornerRadius(self);
 
-    // A single stable shell-wide blur removes the material boundary at the
-    // page edge without stretching Liquid Glass lensing across the content
-    // area. Opaque CEF pages are composited above it in the browser area.
+    // A single stable, non-lensing shell blur removes the material boundary
+    // at the page edge. Window-sized Liquid Glass corrupts its refractive
+    // backing texture on large Retina windows, so native lensing is reserved
+    // for the constant-height chrome and bounded controls above this surface.
+    // Opaque CEF pages are composited above it in the browser area.
     NSView* shellSurface = [[NSView alloc] initWithFrame:frame];
     shellSurface.autoresizingMask = NSViewWidthSizable | NSViewHeightSizable;
-    NSView* shellContent =
-        BroInstallShellSurface(shellSurface, BroShellCornerRadius());
+    BroInstallShellSurface(shellSurface, BroShellCornerRadius());
     [content addSubview:shellSurface];
     _shellSurface = shellSurface;
 
+    // The native refractive surface is restricted to the constant-height
+    // chrome band. Its texture budget therefore stays stable as the window
+    // grows vertically, while AppKit can still render the same Liquid Glass
+    // treatment across the full toolbar width. Older systems use the shell
+    // backdrop directly and avoid stacking two visual-effect materials.
+    CGFloat toolbarY = frame.size.height - kToolbarHeight;
+    NSView* chromeSurface = [[NSView alloc]
+        initWithFrame:NSMakeRect(0, toolbarY, frame.size.width, kToolbarHeight)];
+    chromeSurface.autoresizingMask = NSViewWidthSizable | NSViewMinYMargin;
+    NSView* chromeContent = chromeSurface;
+    if (@available(macOS 26.0, *)) {
+      if (BroShouldUseNativeGlass()) {
+        chromeContent = BroInstallGlassSurface(chromeSurface, 0.0);
+      }
+    }
+    [content addSubview:chromeSurface];
+    _chromeSurface = chromeSurface;
+
     // Single chrome row at the very top; its content is inset past the
     // traffic lights.
-    CGFloat toolbarY = frame.size.height - kToolbarHeight;
     _navToolbar = [[BroToolbar alloc]
-        initWithFrame:NSMakeRect(0, toolbarY, frame.size.width, kToolbarHeight)];
-    [shellContent addSubview:_navToolbar];
+        initWithFrame:NSMakeRect(0, 0, frame.size.width, kToolbarHeight)];
+    [chromeContent addSubview:_navToolbar];
     g_toolbar = _navToolbar;
 
     // Tab strip inline in the toolbar row: after the nav buttons, before the
@@ -1072,9 +1091,8 @@ void UpdateWindowForViewportMode(BOOL mobile, BOOL animate,
 // Cmd+S (View menu) hides the toolbar -- and the tab strip nested inside it,
 // since BroTabBar is one of its subviews -- and the traffic lights, leaving
 // an Arc-style frame: the page sits as a rounded card inset by
-// kScreenshotModeGutter on all four sides, with the window's existing glass
-// (the same material the chrome row already wears -- setGlassBackdropVisible:
-// below) showing through the gutter, and the existing hairline
+// kScreenshotModeGutter on all four sides, with the window's stable shell
+// material showing through the gutter, and the existing hairline
 // (BroWindowBorderView) still tracing the true window edge outside all of
 // it. The active tab's container(s) already fill 100% of browserContainer's
 // bounds in every mode -- desktop, mobile, split -- so animating just
@@ -1161,10 +1179,11 @@ static void ToggleScreenshotMode(void) {
                           contentBounds.size.height - kToolbarHeight);
 
   if (!active) {
-    // Make the toolbar visible again before fading it in -- a hidden view's
-    // alpha animation never draws.
+    // Make the whole glass band visible again before fading it in -- a hidden
+    // view's alpha animation never draws.
+    g_main_window.chromeSurface.hidden = NO;
+    g_main_window.chromeSurface.alphaValue = 0.0;
     g_toolbar.hidden = NO;
-    g_toolbar.alphaValue = 0.0;
   }
 
   // The card's own corner radius derives from the window's (bro_geometry's
@@ -1182,10 +1201,11 @@ static void ToggleScreenshotMode(void) {
       : 0.0;
 
   BroRunLayoutSpring(^{
-    g_toolbar.animator.alphaValue = active ? 0.0 : 1.0;
+    g_main_window.chromeSurface.animator.alphaValue = active ? 0.0 : 1.0;
     g_main_window.browserContainer.animator.frame = containerTarget;
     containerLayer.cornerRadius = cardRadius;
   }, ^{
+    g_main_window.chromeSurface.hidden = active;
     g_toolbar.hidden = active;
     UpdateChromeLayout();  // final snap: exact per-tab/divider frames
     BroHandler* handler = BroHandler::GetInstance();

src/bro_motion.h

@@ -52,21 +52,23 @@ extern void BroRunLayoutSpring(void (^changes)(void),
 
 extern void BroApplyElevation(NSView* view, BroElevation elevation);
 
-// Shared material tokens for every glass surface. macOS 26 uses untinted
+// Shared material tokens for bounded glass surfaces. macOS 26 uses untinted
 // Regular glass; older systems retain an appearance-adaptive HUD fallback.
 extern const CGFloat kBroGlassTintAlpha;
 extern const CGFloat kBroGlassBorderWidth;
 extern NSColor* BroGlassTintColor(void);
 extern NSColor* BroGlassBorderColor(void);
 extern NSGlassEffectViewStyle BroGlassEffectStyle(void)
     API_AVAILABLE(macos(26.0));
-// Runtime gate shared by every native surface. BRO_FORCE_LEGACY_GLASS=1 is a
-// test seam for exercising the macOS 12–25 fallback on a macOS 26 machine.
+// Runtime gate shared by native control and overlay surfaces.
+// BRO_FORCE_LEGACY_GLASS=1 is a test seam for exercising the macOS 12–25
+// fallback on a macOS 26 machine.
 extern BOOL BroShouldUseNativeGlass(void);
 
-// Installs the shell-sized native Liquid Glass backdrop on macOS 26. The
-// returned host is NSGlassEffectView.contentView there; older systems receive
-// the same content over the existing visual-effect fallback.
+// Installs the stable window-sized AppKit backdrop. The shell deliberately
+// stays non-lensing at every OS version because a full-window
+// NSGlassEffectView corrupts its backing texture on large Retina windows;
+// bounded controls and overlays still use native Liquid Glass on macOS 26.
 extern NSView* BroInstallShellSurface(NSView* panel, CGFloat cornerRadius);
 
 // Replaces the elevation's flat fill with the shared glass surface and
@@ -75,10 +77,6 @@ extern NSView* BroInstallShellSurface(NSView* panel, CGFloat cornerRadius);
 // the existing HUD blur + tint.
 // Call after BroApplyElevation and add all visible content to the result.
 extern NSView* BroInstallGlassSurface(NSView* panel, CGFloat cornerRadius);
-// Wraps related glass descendants in AppKit's batching/merging container on
-// macOS 26 and returns |contentView| unchanged on the legacy path.
-extern NSView* BroGlassContainerForContentView(NSView* contentView,
-                                               CGFloat spacing);
 extern void BroOverlayShow(NSView* view);
 extern void BroOverlayHide(NSView* view);
 

src/bro_motion.mm

@@ -329,23 +329,22 @@ - (void)viewDidChangeEffectiveAppearance {
   CGFloat backdropRadius = BroCornerRadiusForSize(
       BroNestedCornerRadius(cornerRadius, 0.0), panel.bounds.size);
 
-  if (@available(macOS 26.0, *)) {
-    if (BroShouldUseNativeGlass()) {
-      NSGlassEffectView* glass =
-          [[NSGlassEffectView alloc] initWithFrame:panel.bounds];
-      glass.cornerRadius = backdropRadius;
-      glass.style = BroGlassEffectStyle();
-      glass.tintColor = nil;
-      NSView* contentHost = [[NSView alloc] initWithFrame:glass.bounds];
-      contentHost.autoresizingMask = NSViewWidthSizable | NSViewHeightSizable;
-      glass.contentView = contentHost;
-      BroPinView(glass, panel);
-      return contentHost;
-    }
-  }
+  // Keep the window-sized shell on AppKit's non-lensing material. A regular
+  // NSGlassEffectView allocates a refractive backdrop for its whole bounds;
+  // once a Retina window grows large enough, that surface starts dropping or
+  // stretching texture tiles during live move/resize. Liquid Glass remains on
+  // the bounded controls and overlays above this backdrop, where AppKit can
+  // render and batch it reliably.
+  //
+  // Under-window background is the native macOS 26 shell material. Older
+  // systems retain the established HUD blur.
   NSVisualEffectView* backdrop =
       [[NSVisualEffectView alloc] initWithFrame:panel.bounds];
-  backdrop.material = NSVisualEffectMaterialHUDWindow;
+  if (@available(macOS 26.0, *)) {
+    backdrop.material = NSVisualEffectMaterialUnderWindowBackground;
+  } else {
+    backdrop.material = NSVisualEffectMaterialHUDWindow;
+  }
   backdrop.blendingMode = NSVisualEffectBlendingModeBehindWindow;
   backdrop.state = NSVisualEffectStateActive;
   backdrop.wantsLayer = YES;
@@ -417,24 +416,6 @@ - (void)viewDidChangeEffectiveAppearance {
   return contentHost;
 }
 
-NSView* BroGlassContainerForContentView(NSView* contentView,
-                                        CGFloat spacing) {
-  if (!contentView) {
-    return nil;
-  }
-  if (@available(macOS 26.0, *)) {
-    if (BroShouldUseNativeGlass()) {
-      NSGlassEffectContainerView* container =
-          [[NSGlassEffectContainerView alloc]
-              initWithFrame:contentView.frame];
-      container.spacing = MAX(0.0, spacing);
-      container.contentView = contentView;
-      return container;
-    }
-  }
-  return contentView;
-}
-
 void BroOverlayShow(NSView* view) {
   if (!view) {
     return;

src/bro_tabstrip.mm

@@ -20,7 +20,6 @@
 static const CGFloat kHoveredTabBorderAlpha = 0.18;
 // Resting pills keep the strip's 8pt gap. As a dragged pill comes within 6pt
 // of a neighbor, AppKit's glass container performs the native merge/split.
-static const CGFloat kTabGlassMergeSpacing = 6.0;
 static const CFTimeInterval kTabColorTransitionDuration = 0.18;
 
 static NSDictionary* BroTabLayerTransitionActions(void) {
@@ -419,9 +418,10 @@ void BroFetchFaviconGuarded(NSString* urlString,
 }
 
 @implementation BroTabView {
-  // Every macOS 26 pill owns a native glass descendant so the tab strip's
-  // NSGlassEffectContainerView can batch it and merge neighboring pills
-  // during drag. Older systems retain the established HUD fallback.
+  // Every macOS 26 pill owns a bounded native glass descendant. Keeping each
+  // effect independent prevents AppKit's rectangular batch texture from
+  // leaking behind the strip on large Retina windows. Older systems retain
+  // the established HUD fallback.
   NSView* glassBackdrop_;
   NSView* pillContentHost_;
   BOOL nativeGlassBackdrop_;
@@ -461,8 +461,7 @@ - (instancetype)initWithFrame:(NSRect)frame browserId:(int)browserId {
     self.focusRingType = NSFocusRingTypeNone;
 
     // Native pills stay neutral; selection is layered through adaptive
-    // content and a restrained fill so all descendants remain sufficiently
-    // similar for NSGlassEffectContainerView to merge them.
+    // content and a restrained fill.
     if (@available(macOS 26.0, *)) {
       if (BroShouldUseNativeGlass()) {
         NSGlassEffectView* glass =
@@ -1411,7 +1410,6 @@ - (void)scrollWheel:(NSEvent*)event {
 
 @implementation BroTabBar {
   BroHorizontalTabScrollView* tabScrollView_;
-  NSView* tabDocumentView_;
   NSView* tabContentView_;
   BroTabView* draggingTab_;
   BOOL dragging_;
@@ -1464,9 +1462,7 @@ - (instancetype)initWithFrame:(NSRect)frame {
     tabContentView_ =
         [[NSView alloc] initWithFrame:NSMakeRect(0, 0, 0, frame.size.height)];
     tabContentView_.wantsLayer = YES;
-    tabDocumentView_ = BroGlassContainerForContentView(
-        tabContentView_, kTabGlassMergeSpacing);
-    tabScrollView_.documentView = tabDocumentView_;
+    tabScrollView_.documentView = tabContentView_;
     [self addSubview:tabScrollView_];
 
     // Borderless "+" control, pinned between the scroll viewport and Search.
@@ -2113,8 +2109,7 @@ - (void)layOutTabsThroughAnimator {
   }
 
   CGFloat documentWidth = MAX(viewportWidth, x);
-  tabDocumentView_.frame = NSMakeRect(0, 0, documentWidth, height);
-  tabContentView_.frame = tabDocumentView_.bounds;
+  tabContentView_.frame = NSMakeRect(0, 0, documentWidth, height);
   [self clampScrollOffset];
 
   // The "+" trails the last pill by one gap (`x` already carries it) so it

tests/bro_glass_surface_tests.mm

@@ -32,19 +32,29 @@ int main(void) {
     if (@available(macOS 26.0, *)) {
       unsetenv("BRO_FORCE_LEGACY_GLASS");
       NSView* shell = [[NSView alloc]
-          initWithFrame:NSMakeRect(0, 0, 640, 480)];
+          initWithFrame:NSMakeRect(0, 0, 2560, 1440)];
       NSView* shellContent = BroInstallShellSurface(shell, 12.0);
-      NSGlassEffectView* shellGlass = (NSGlassEffectView*)
-          FindSubviewOfClass(shell, [NSGlassEffectView class]);
-      Require(shellGlass != nil, @"shell must use NSGlassEffectView");
-      Require(shellGlass.contentView == shellContent,
-              @"shell controls must live in native contentView");
-      Require(shellGlass.style == NSGlassEffectViewStyleRegular,
-              @"shell must use Regular glass");
-      Require(shellGlass.tintColor == nil,
-              @"shell glass must remain neutral");
-      Require(fabs(shellGlass.cornerRadius - 12.0) < 0.01,
-              @"shell radius must be handed to AppKit");
+      NSVisualEffectView* shellBackdrop = (NSVisualEffectView*)
+          FindSubviewOfClass(shell, [NSVisualEffectView class]);
+      Require(shellBackdrop != nil,
+              @"large shell must use the stable visual-effect backdrop");
+      Require(FindSubviewOfClass(shell, [NSGlassEffectView class]) == nil,
+              @"large shell must not allocate a window-sized glass texture");
+      Require(shellBackdrop.material ==
+                  NSVisualEffectMaterialUnderWindowBackground,
+              @"macOS 26 shell must use the under-window material");
+      Require(shellContent.superview == shell,
+              @"shell content host must remain above the stable backdrop");
+
+      NSView* chrome = [[NSView alloc]
+          initWithFrame:NSMakeRect(0, 0, 2560, 52)];
+      NSView* chromeContent = BroInstallGlassSurface(chrome, 0.0);
+      NSGlassEffectView* chromeGlass = (NSGlassEffectView*)
+          FindSubviewOfClass(chrome, [NSGlassEffectView class]);
+      Require(chromeGlass != nil,
+              @"wide constant-height chrome must retain native glass");
+      Require(chromeGlass.contentView == chromeContent,
+              @"chrome controls must live in native contentView");
 
       NSView* panel = [[NSView alloc]
           initWithFrame:NSMakeRect(0, 0, 320, 180)];
@@ -58,18 +68,6 @@ int main(void) {
       Require(fabs(panelGlass.cornerRadius - 10.0) < 0.01,
               @"overlay radius must be handed to AppKit");
 
-      NSView* tabs = [[NSView alloc]
-          initWithFrame:NSMakeRect(0, 0, 600, 52)];
-      NSView* tabDocument = BroGlassContainerForContentView(tabs, 6.0);
-      Require([tabDocument isKindOfClass:[NSGlassEffectContainerView class]],
-              @"tab content must use NSGlassEffectContainerView");
-      NSGlassEffectContainerView* tabContainer =
-          (NSGlassEffectContainerView*)tabDocument;
-      Require(tabContainer.contentView == tabs,
-              @"tab content must be owned by the native container");
-      Require(fabs(tabContainer.spacing - 6.0) < 0.01,
-              @"tab merge proximity must be handed to AppKit");
-
       setenv("BRO_FORCE_LEGACY_GLASS", "1", 1);
       NSView* fallback = [[NSView alloc]
           initWithFrame:NSMakeRect(0, 0, 320, 180)];
@@ -80,11 +78,6 @@ int main(void) {
               @"forced fallback must retain NSVisualEffectView");
       Require(fallbackContent.superview == fallback,
               @"fallback content host must remain usable");
-      NSView* fallbackTabs = [[NSView alloc]
-          initWithFrame:NSMakeRect(0, 0, 600, 52)];
-      Require(BroGlassContainerForContentView(fallbackTabs, 6.0) ==
-                  fallbackTabs,
-              @"legacy tab content must bypass the unavailable container");
     }
   }
   return 0;