fix(tool): Fixes ExitLoopTool by adding Schema and description

- The description now matches the prompt in python.
- Also add it to ComponentRegistry for use in ADK Config.

PiperOrigin-RevId: 795350942

Author: Jacksunwei

core/src/main/java/com/google/adk/tools/ExitLoopTool.java

@@ -16,11 +16,32 @@
 
 package com.google.adk.tools;
 
-/** Exits the loop. */
+import com.google.adk.tools.Annotations.Schema;
+
+/** Tool for exiting execution of {@link com.google.adk.agents.LoopAgent}. */
 public final class ExitLoopTool {
+  public static final FunctionTool INSTANCE = FunctionTool.create(ExitLoopTool.class, "exitLoop");
+
+  /**
+   * Exit the {@link com.google.adk.agents.LoopAgent} execution.
+   *
+   * <p>Usage example in an LlmAgent:
+   *
+   * <pre>{@code
+   * LlmAgent subAgent = LlmAgent.builder()
+   *     .addTool(ExitLoopTool.INSTANCE)
+   *     .build();
+   * }</pre>
+   *
+   * <p>The @Schema name and description is consistent with the Python version.
+   *
+   * <p>Refer to:
+   * https://github.com/google/adk-python/blob/main/src/google/adk/tools/exit_loop_tool.py
+   */
+  @Schema(
+      name = "exit_loop",
+      description = "Exits the loop.\n\nCall this function only when you are instructed to do so.")
   public static void exitLoop(ToolContext toolContext) {
-    // Exits the loop.
-    // Call this function only when you are instructed to do so.
     toolContext.setActions(toolContext.actions().toBuilder().escalate(true).build());
   }
 

core/src/main/java/com/google/adk/utils/ComponentRegistry.java

@@ -25,6 +25,7 @@
 import com.google.adk.agents.SequentialAgent;
 import com.google.adk.tools.AgentTool;
 import com.google.adk.tools.BaseTool;
+import com.google.adk.tools.ExitLoopTool;
 import com.google.adk.tools.GoogleSearchTool;
 import com.google.adk.tools.LoadArtifactsTool;
 import java.util.Map;
@@ -97,6 +98,7 @@ private void initializePreWiredEntries() {
 
     registerAdkToolInstance("google_search", new GoogleSearchTool());
     registerAdkToolInstance("load_artifacts", new LoadArtifactsTool());
+    registerAdkToolInstance("exit_loop", ExitLoopTool.INSTANCE);
 
     registerAdkToolClass(AgentTool.class);
     // TODO: add all python tools that also exist in Java.