Integrate App Engine Task Queue API with Google Cloud Tasks.

This change introduces support for routing App Engine push queues to Google Cloud Tasks when the APPENGINE_USE_CLOUDTASK_PUSH_QUEUE environment variable is enabled.
Key changes include:
- Adding CloudTasksClientWrapper to handle task creation, deletion, purging, and statistics using the Cloud Tasks SDK and REST API.
- Implementing transactional task queuing via a Datastore-backed buffer (_AE_PendingCloudTask) and a background sweeper (SweeperServlet and TaskProcessor) to guarantee delivery.
- Introducing RequestCachingFilter to cache task request payloads and handle sweep triggers.
- Updating QueueImpl to delegate push queue operations to the new Cloud Tasks integration.
- Updating Maven and Bazel build files to include the required Google Cloud Tasks, GAX, and proto dependencies.

PiperOrigin-RevId: 965724714
Change-Id: Idd794e9528d0f8918b03e5a7fbf7656f902e6124

Author: gae-java-bot

api/pom.xml

@@ -122,6 +122,10 @@
       <groupId>javax.servlet</groupId>
       <artifactId>javax.servlet-api</artifactId>
     </dependency>
+    <dependency>
+      <groupId>com.google.cloud</groupId>
+      <artifactId>google-cloud-tasks</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.antlr</groupId>
       <artifactId>antlr-runtime</artifactId>

api/src/main/java/com/google/appengine/api/datastore/DatastoreApiHelper.java

@@ -56,6 +56,16 @@ public final class DatastoreApiHelper {
 
   private DatastoreApiHelper() {}
 
+  /**
+   * Registers a callback to be executed immediately after the specified transaction commits.
+   * If the transaction is rolled back or fails to commit, the callback will not be invoked.
+   */
+  public static void addPostCommitCallback(Transaction txn, Runnable callback) {
+    if (txn instanceof TransactionImpl txnImpl && callback != null) {
+      txnImpl.addPostCommitCallback(callback);
+    }
+  }
+
   // Corresponds to _ToDatastoreError in datastore.py.
   // Keep in sync!
   public static RuntimeException translateError(ApiProxy.ApplicationException exception) {

api/src/main/java/com/google/appengine/api/datastore/TransactionImpl.java

@@ -81,6 +81,14 @@ enum TransactionState {
 
   TransactionState state = TransactionState.BEGUN;
 
+  private final List<Runnable> postCommitCallbacks = new java.util.concurrent.CopyOnWriteArrayList<>();
+
+  void addPostCommitCallback(Runnable callback) {
+    if (callback != null) {
+      postCommitCallbacks.add(callback);
+    }
+  }
+
   /** A {@link PostOpFuture} implementation that runs both post put and post delete callbacks. */
   private class PostCommitFuture extends PostOpFuture<Void> {
     private final List<Entity> putEntities;
@@ -100,6 +108,13 @@ void executeCallbacks(Void ignoreMe) {
       DeleteContext deleteContext =
           new DeleteContext(TransactionImpl.this, TransactionImpl.this, deletedKeys);
       callbacks.executePostDeleteCallbacks(deleteContext);
+      for (Runnable callback : postCommitCallbacks) {
+        try {
+          callback.run();
+        } catch (Throwable t) {
+          logger.log(Level.SEVERE, "Exception in post-commit callback: " + t.getMessage(), t);
+        }
+      }
     }
   }