Clipping a very long child using a RoundedSuperellipseBorder produces artifacts

### Steps to reproduce

1. Create a Container() with `decoration: ShapeDecoration(shape: RoundedSuperellipseBorder(borderRadius: .circular(32)))` and `clipBehavior: .antiAlias`
2. Put a very long child inside the container.

### Expected results

The child is clipped with a superellipse-shaped Container smoothly, just like when using ClipRSuperellipse.

### Actual results

There are visual artifacts around the corners.

### Code sample

<details open><summary>Code sample (with visual glitches)</summary>

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: SingleChildScrollView(
          child: Padding(
            padding: const .all(32),
            child: Container(
              decoration: ShapeDecoration(
                shape: RoundedSuperellipseBorder(borderRadius: .circular(32)),
              ),
              clipBehavior: .antiAlias,
              child: Column(
                children: [
                  for (var i = 0; i < 1_000 /* or 10_000 */; i++)
                    Container(
                      height: 32,
                      color: Colors.primaries[i % Colors.primaries.length],
                    ),
                ],
              ),
            ),
          ),
        ),
      ),
    ),
  );
}
```

</details>

<details open><summary>Code sample (displays correctly)</summary>

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: SingleChildScrollView(
          child: Padding(
            padding: const .all(32),
            child: ClipRSuperellipse(
              borderRadius: .circular(32),
              child: Column(
                children: [
                  for (var i = 0; i < 10_000; i++)
                    Container(
                      height: 32,
                      color: Colors.primaries[i % Colors.primaries.length],
                    ),
                ],
              ),
            ),
          ),
        ),
      ),
    ),
  );
}
```

</details>


### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>

***All screenshots taken on macOS 26.2***

For 1K children:

<img width="661" height="224" alt="Image" src="https://github.com/user-attachments/assets/2848fc23-f437-44f6-bc6b-50c67335e8b7" />

<hr>

For 10K children:

<img width="662" height="377" alt="Image" src="https://github.com/user-attachments/assets/674ebd5f-f4f8-4e37-a541-1a91014f1f14" />

<hr>

The same, but with ClipRSuperellipse:

<img width="664" height="325" alt="Image" src="https://github.com/user-attachments/assets/9ea3dd87-680e-4b61-8908-56520849eb0f" />

</details>


### Logs

<details open><summary>Logs</summary>

```console
[Paste your logs here]
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
[✓] Flutter (Channel master, 3.40.0-1.0.pre-109, on macOS 26.2 25C56 darwin-arm64, locale en-US) [1,450ms]
    • Flutter version 3.40.0-1.0.pre-109 on channel master at /Users/piotr/fvm/versions/master
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 9cc43f13a5 (5 days ago), 2025-12-10 21:15:09 +0300
    • Engine revision 5b74a3b8e8
    • Dart version 3.11.0 (build 3.11.0-227.0.dev)
    • DevTools version 2.53.0
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations, enable-native-assets, enable-dart-data-assets, enable-swift-package-manager, omit-legacy-version-file, enable-lldb-debugging, no-enable-uiscene-migration

[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0-rc1) [1,465ms]
    • Android SDK at /Users/piotr/Library/Android/sdk
    • Emulator version 36.3.10.0 (build_id 14472402) (CL:N/A)
    • Platform android-36, build-tools 36.1.0-rc1
    • ANDROID_HOME = /Users/piotr/Library/Android/sdk
    • Java binary at: /Users/piotr/Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
      This is the JDK bundled with the latest Android Studio installation on this machine.
      To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment (build 21.0.8+-14196175-b1038.72)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 26.2) [1,280ms]
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 17C52
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web [5ms]
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Connected device (3 available) [6.6s]
    • Pixel 8 Pro (mobile) • 3C201FDJG00376 • android-arm64  • Android 16 (API 36)
    • macOS (desktop)      • macos          • darwin-arm64   • macOS 26.2 25C56 darwin-arm64
    • Chrome (web)         • chrome         • web-javascript • Google Chrome 143.0.7499.41

[✓] Network resources [243ms]
    • All expected network resources are available.

• No issues found!

```

</details>


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Clipping a very long child using a RoundedSuperellipseBorder produces artifacts #179875

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Uh oh!

Clipping a very long child using a RoundedSuperellipseBorder produces artifacts #179875

Description

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Video

Logs

Flutter Doctor output

Metadata

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

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