diff --git a/app/lib/pages/shell_page.dart b/app/lib/pages/shell_page.dart
index 2f7b51a..01aa278 100644
--- a/app/lib/pages/shell_page.dart
+++ b/app/lib/pages/shell_page.dart
@@ -50,7 +50,11 @@ class _ShellPageState extends State<ShellPage> {
               ),
               child: Column(
                 children: [
-                  const DeltaMark(size: 36),
+                  // Static in the persistent nav rail: a 60fps pulse
+                  // here repaints every scroll frame and stutters web
+                  // scrolling. The breathing mark stays on the
+                  // landing page (which isn't scrolled).
+                  const DeltaMark(size: 36, animated: false),
                   const SizedBox(height: ReclaimSpace.sm),
                   const BrandWordmark(size: 18),
                   Text(
diff --git a/app/lib/widgets/delta_mark.dart b/app/lib/widgets/delta_mark.dart
index fd921cb..6ed7398 100644
--- a/app/lib/widgets/delta_mark.dart
+++ b/app/lib/widgets/delta_mark.dart
@@ -46,17 +46,30 @@ class _DeltaMarkState extends State<DeltaMark>
 
   @override
   Widget build(BuildContext context) {
-    return AnimatedBuilder(
-      animation: _controller,
-      builder: (context, _) {
-        final t = _controller.value;
-        // Breathe: scale 1 → 1.28 → 1 over the cycle.
-        final pulse = 1.0 + 0.28 * (1 - (math.cos(t * 2 * math.pi).abs()));
-        return CustomPaint(
-          size: Size.square(widget.size),
-          painter: _DeltaPainter(pulse: widget.animated ? pulse : 1.0),
-        );
-      },
+    // Static mark: no controller listening, paint once.
+    if (!widget.animated) {
+      return CustomPaint(
+        size: Size.square(widget.size),
+        painter: _DeltaPainter(pulse: 1.0),
+      );
+    }
+    // Animated: isolate the per-frame repaint in its own layer so
+    // the breathing pulse never invalidates surrounding content
+    // (web scroll stays smooth).
+    return RepaintBoundary(
+      child: AnimatedBuilder(
+        animation: _controller,
+        builder: (context, _) {
+          final t = _controller.value;
+          // Breathe: scale 1 → 1.28 → 1 over the cycle.
+          final pulse =
+              1.0 + 0.28 * (1 - (math.cos(t * 2 * math.pi).abs()));
+          return CustomPaint(
+            size: Size.square(widget.size),
+            painter: _DeltaPainter(pulse: pulse),
+          );
+        },
+      ),
     );
   }
 }