Refine milky Dock and refract symbols beneath the moving lens

mobile/test/widgets/dock_motion_test.dart

@@ -11,6 +11,36 @@ import 'navigation_test.dart' show uiController;
 
 void main() {
   setUpAll(tzdata.initializeTimeZones);
+  testWidgets(
+    'moving lens refracts symbols above the icon row and releases cleanly',
+    (tester) async {
+      await tester.pumpWidget(_dock());
+      await tester.pumpAndSettle();
+      final optical = find.byKey(const ValueKey('dock-symbol-refraction'));
+      expect(optical, findsNothing);
+      final gesture = await tester.startGesture(
+        tester.getCenter(find.byKey(const Key('dock-cursor'))),
+      );
+      await gesture.moveBy(const Offset(24, 0));
+      await tester.pump();
+      await gesture.moveBy(const Offset(54, 0));
+      await tester.pump(const Duration(milliseconds: 120));
+      expect(optical, findsOneWidget);
+      final filter = tester.widget<GlassRefraction>(
+        find.descendant(of: optical, matching: find.byType(GlassRefraction)),
+      );
+      expect(filter.strength, greaterThan(0.35));
+      expect(filter.blurSigma, 0); // Keep the transmitted symbols legible.
+      final stack = tester.widget<Stack>(
+        find.ancestor(of: optical, matching: find.byType(Stack)).first,
+      );
+      expect(stack.children.last.key, const ValueKey('dock-symbol-refraction'));
+      await gesture.up();
+      await tester.pumpAndSettle();
+      expect(optical, findsNothing);
+      expect(tester.takeException(), isNull);
+    },
+  );
   testWidgets('edge overflow respects the actual dock parent and safe insets', (
     tester,
   ) async {