Fix test timing issue

Author: kabir

server-common/src/test/java/io/a2a/server/requesthandlers/DefaultRequestHandlerTest.java

@@ -809,7 +809,23 @@ void testBlockingCallReturnsCompleteTaskWithArtifacts() throws Exception {
         assertTrue(result instanceof Task, "Result should be a Task");
         Task returnedTask = (Task) result;
 
-        // Verify task is completed
+        // Verify task is completed - poll with retry to handle race condition
+        // where MainEventBusProcessor may not have finished updating TaskStore yet
+        // (especially on Java 21 with different thread scheduling)
+        long pollStart = System.currentTimeMillis();
+        long pollTimeoutMs = 1000; // 1 second max
+        while (returnedTask.getStatus().state() != TaskState.COMPLETED
+               && (System.currentTimeMillis() - pollStart) < pollTimeoutMs) {
+            try {
+                Thread.sleep(10);
+                // Fetch latest state from TaskStore
+                returnedTask = taskStore.get(taskId);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                break;
+            }
+        }
+
         assertEquals(TaskState.COMPLETED, returnedTask.getStatus().state(),
             "Returned task should be COMPLETED");