feat: Adding plugin(Plugin... p) helper methods on App and Runner builders

core/src/main/java/com/google/adk/apps/App.java

@@ -104,6 +104,12 @@ public Builder plugins(List<? extends Plugin> plugins) {
       return this;
     }
 
+    @CanIgnoreReturnValue
+    public Builder plugins(Plugin... plugins) {
+      this.plugins = ImmutableList.copyOf(plugins);
+      return this;
+    }
+
     @CanIgnoreReturnValue
     public Builder eventsCompactionConfig(EventsCompactionConfig eventsCompactionConfig) {
       this.eventsCompactionConfig = eventsCompactionConfig;

core/src/main/java/com/google/adk/plugins/PluginManager.java

@@ -23,6 +23,8 @@
 import com.google.adk.models.LlmResponse;
 import com.google.adk.tools.BaseTool;
 import com.google.adk.tools.ToolContext;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableList;
 import com.google.genai.types.Content;
 import io.reactivex.rxjava3.core.Completable;
 import io.reactivex.rxjava3.core.Flowable;
@@ -81,6 +83,21 @@ public Optional<Plugin> getPlugin(String pluginName) {
     return plugins.stream().filter(p -> p.getName().equals(pluginName)).findFirst();
   }
 
+  /**
+   * Returns the list of registered plugins.
+   *
+   * <p>This method is intended for testing purposes only.
+   *
+   * <p>Note that it returns a copy of the plugins list to prevent modification of the original
+   * list.
+   *
+   * @return The list of registered plugins.
+   */
+  @VisibleForTesting
+  public List<Plugin> getPlugins() {
+    return ImmutableList.copyOf(plugins);
+  }
+
   // --- Callback Runners ---
 
   public Maybe<Content> runOnUserMessageCallback(

core/src/main/java/com/google/adk/runner/Runner.java

@@ -132,6 +132,13 @@ public Builder plugins(List<? extends Plugin> plugins) {
       return this;
     }
 
+    @CanIgnoreReturnValue
+    public Builder plugins(Plugin... plugins) {
+      Preconditions.checkState(this.app == null, "plugins() cannot be called when app is set.");
+      this.plugins = ImmutableList.copyOf(plugins);
+      return this;
+    }
+
     public Runner build() {
       BaseAgent buildAgent;
       String buildAppName;

core/src/test/java/com/google/adk/runner/RunnerTest.java

@@ -1188,6 +1188,14 @@ public void close_closesPluginsAndCodeExecutors() {
     verify(plugin).close();
   }
 
+  @Test
+  public void buildRunnerWithPlugins_success() {
+    BasePlugin plugin1 = mockPlugin("test1");
+    BasePlugin plugin2 = mockPlugin("test2");
+    Runner runner = Runner.builder().agent(agent).appName("test").plugins(plugin1, plugin2).build();
+    assertThat(runner.pluginManager().getPlugins()).containsExactly(plugin1, plugin2);
+  }
+
   public static class Tools {
     private Tools() {}