fix: merge metadata instead of replacing in TaskManager.TaskStatusUpdateEvent #426 (#427)

Author: flex-myeonghyeon

server-common/src/main/java/io/a2a/server/tasks/TaskManager.java

@@ -5,7 +5,9 @@
 import static io.a2a.util.Utils.appendArtifactToTask;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 import io.a2a.spec.A2AServerException;
 import io.a2a.spec.Artifact;
@@ -78,7 +80,9 @@ Task saveTaskEvent(TaskStatusUpdateEvent event) throws A2AServerException {
 
         // Handle metadata from the event
         if (event.getMetadata() != null) {
-            builder.metadata(event.getMetadata());
+            Map<String, Object> metadata = task.getMetadata() == null ? new HashMap<>() : new HashMap<>(task.getMetadata());
+            metadata.putAll(event.getMetadata());
+            builder.metadata(metadata);
         }
 
         task = builder.build();

server-common/src/test/java/io/a2a/server/tasks/TaskManagerTest.java

@@ -588,8 +588,8 @@ public void testSaveTaskEventMetadataUpdateNull() throws A2AServerException {
     }
 
     @Test
-    public void testSaveTaskEventMetadataUpdateOverwritesExisting() throws A2AServerException {
-        // Test that metadata update overwrites existing metadata
+    public void testSaveTaskEventMetadataMergeExisting() throws A2AServerException {
+        // Test that metadata update merges with existing metadata
         Map<String, Object> originalMetadata = new HashMap<>();
         originalMetadata.put("original_key", "original_value");
 
@@ -612,8 +612,10 @@ public void testSaveTaskEventMetadataUpdateOverwritesExisting() throws A2AServer
         taskManager.saveTaskEvent(event);
 
         Task updatedTask = taskManager.getTask();
-        assertEquals(newMetadata, updatedTask.getMetadata());
-        assertNotEquals(originalMetadata, updatedTask.getMetadata());
+
+        Map<String, Object> mergedMetadata = new HashMap<>(originalMetadata);
+        mergedMetadata.putAll(newMetadata);
+        assertEquals(mergedMetadata, updatedTask.getMetadata());
     }
 
     @Test