fix: Use correct HTTP status code for PushNotificationNotSupportedError (#758)

Fixes #748  🦕

Author: kabir

transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java

@@ -776,8 +776,7 @@ private static int mapErrorToHttpStatus(A2AError error) {
         if (error instanceof TaskNotCancelableError) {
             return 409;
         }
-        if (error instanceof PushNotificationNotSupportedError
-                || error instanceof UnsupportedOperationError) {
+        if (error instanceof UnsupportedOperationError) {
             return 501;
         }
         if (error instanceof ContentTypeNotSupportedError) {
@@ -788,7 +787,8 @@ private static int mapErrorToHttpStatus(A2AError error) {
         }
         if (error instanceof ExtendedAgentCardNotConfiguredError
                 || error instanceof ExtensionSupportRequiredError
-                || error instanceof VersionNotSupportedError) {
+                || error instanceof VersionNotSupportedError
+                || error instanceof PushNotificationNotSupportedError) {
             return 400;
         }
         if (error instanceof InternalError) {

transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java

@@ -388,7 +388,7 @@ public void testPushNotificationConfigNotSupported() {
 
         RestHandler.HTTPRestResponse response = handler.createTaskPushNotificationConfiguration(callContext, "", requestBody, MINIMAL_TASK.id());
 
-        assertProblemDetail(response, 501,
+        assertProblemDetail(response, 400,
                 "https://a2a-protocol.org/errors/push-notification-not-supported",
                 "Push Notification is not supported");
     }