fix cupertino refresh control style (#79842)

packages/flutter/lib/src/cupertino/refresh.dart

@@ -420,7 +420,7 @@ class CupertinoSliverRefreshControl extends StatefulWidget {
     double refreshTriggerPullDistance,
     double refreshIndicatorExtent,
   ) {
-    final double percentageComplete = pulledExtent / refreshTriggerPullDistance;
+    final double percentageComplete = (pulledExtent / refreshTriggerPullDistance).clamp(0.0, 1.0);
 
     // Place the indicator at the top of the sliver that opens up. Note that we're using
     // a Stack/Positioned widget because the CupertinoActivityIndicator does some internal

packages/flutter/test/cupertino/refresh_test.dart

@@ -1322,6 +1322,26 @@ void main() {
       );
       expect(tester.widget<CupertinoActivityIndicator>(find.byType(CupertinoActivityIndicator)).progress, 100.0 / 100.0);
     });
+
+    testWidgets('indicator should not become larger when overscrolled', (WidgetTester tester) async {
+      // test for https://github.com/flutter/flutter/issues/79841
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: Builder(
+            builder: (BuildContext context) {
+              return CupertinoSliverRefreshControl.buildRefreshIndicator(
+                context,
+                RefreshIndicatorMode.done,
+                120, 100, 10,
+              );
+            },
+          ),
+        ),
+      );
+
+      expect(tester.widget<CupertinoActivityIndicator>(find.byType(CupertinoActivityIndicator)).radius, 14.0);
+    });
   }
 
   group('UI tests long list', uiTestGroup);