alias the master channel to main

pkgs/sketch_pad/lib/model.dart

@@ -410,6 +410,11 @@ enum Channel {
   static Channel? forName(String name) {
     name = name.trim().toLowerCase();
 
+    // Alias 'master' to 'main'.
+    if (name == 'master') {
+      name = 'main';
+    }
+
     return Channel.values.firstWhereOrNull((c) => c.name == name);
   }
 }

pkgs/sketch_pad/test/model_test.dart

@@ -0,0 +1,29 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:sketch_pad/model.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Channel', () {
+    test('master is aliased', () {
+      final value = Channel.forName('master');
+      expect(value?.name, 'main');
+    });
+
+    test('supported channels', () {
+      final result = Channel.valuesWithoutLocalhost.map((c) => c.name).toList();
+      expect(
+        result,
+        unorderedMatches(
+          [
+            'main',
+            'beta',
+            'stable',
+          ],
+        ),
+      );
+    });
+  });
+}