Add Test and Java doc for WorkflowInstance.output

impl/core/src/main/java/io/serverlessworkflow/impl/WorkflowInstance.java

@@ -25,4 +25,28 @@ public interface WorkflowInstance extends WorkflowInstanceData {
   boolean cancel();
 
   boolean resume();
+
+  /**
+   * Returns the workflow output.
+   *
+   * <p>This method may block until the workflow execution has completed. Callers should not invoke
+   * it from lifecycle callbacks, listener threads, or other execution contexts where blocking is
+   * not safe.
+   *
+   * @return the workflow output
+   */
+  WorkflowModel output();
+
+  /**
+   * Returns the workflow output converted to the requested type.
+   *
+   * <p>This method may block until the workflow execution has completed. Callers should not invoke
+   * it from lifecycle callbacks, listener threads, or other execution contexts where blocking is
+   * not safe.
+   *
+   * @param clazz the target output type
+   * @param <T> the target output type
+   * @return the workflow output converted to {@code clazz}
+   */
+  <T> T outputAs(Class<T> clazz);
 }

impl/core/src/main/java/io/serverlessworkflow/impl/WorkflowInstanceData.java

@@ -28,9 +28,5 @@ public interface WorkflowInstanceData {
 
   WorkflowStatus status();
 
-  WorkflowModel output();
-
   WorkflowModel context();
-
-  <T> T outputAs(Class<T> clazz);
 }

impl/test/src/test/java/io/serverlessworkflow/impl/test/WorkflowExecutionListenerOutputTest.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.serverlessworkflow.impl.test;
+
+import static io.serverlessworkflow.api.WorkflowReader.readWorkflowFromClasspath;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.serverlessworkflow.impl.WorkflowApplication;
+import io.serverlessworkflow.impl.WorkflowModel;
+import io.serverlessworkflow.impl.lifecycle.WorkflowCompletedEvent;
+import io.serverlessworkflow.impl.lifecycle.WorkflowExecutionListener;
+import java.io.IOException;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Verifies that {@code event.output()} in {@code onWorkflowCompleted} carries the workflow's final
+ * output. {@code WorkflowCompletedEvent.output()} is the correct API for accessing output inside
+ * the hook — it is populated directly from the task result before the event is published.
+ *
+ * <p>{@code instanceData().output()} is intentionally absent from {@link
+ * io.serverlessworkflow.impl.WorkflowInstanceData}: it is a blocking join on the workflow future
+ * intended for callers outside the event chain (e.g. after {@code instance.start().join()}).
+ */
+class WorkflowExecutionListenerOutputTest {
+
+  @Test
+  void eventOutputIsPopulatedInOnWorkflowCompleted() throws IOException {
+    AtomicReference<WorkflowModel> capturedOutput = new AtomicReference<>();
+
+    WorkflowExecutionListener listener =
+        new WorkflowExecutionListener() {
+          @Override
+          public void onWorkflowCompleted(WorkflowCompletedEvent event) {
+            capturedOutput.set(event.output());
+          }
+        };
+
+    try (WorkflowApplication app = WorkflowApplication.builder().withListener(listener).build()) {
+      WorkflowModel result =
+          app.workflowDefinition(
+                  readWorkflowFromClasspath("workflows-samples/simple-expression.yaml"))
+              .instance(Map.of())
+              .start()
+              .join();
+
+      assertThat(capturedOutput.get())
+          .as("event.output() must be non-null in onWorkflowCompleted")
+          .isNotNull();
+      assertThat(capturedOutput.get().asMap())
+          .as("event.output() must equal the workflow's final output")
+          .isEqualTo(result.asMap());
+    }
+  }
+}