Add error handling for plan&execute agent

ml-algorithms/src/main/java/org/opensearch/ml/engine/algorithms/agent/MLChatAgentRunner.java

@@ -701,7 +701,13 @@ private static void runTool(
                         );
                     nextStepListener
                         .onResponse(
-                            String.format(Locale.ROOT, "Failed to run the tool %s with the error message %s.", finalAction, e.getMessage())
+                            String
+                                .format(
+                                    Locale.ROOT,
+                                    "Failed to run the tool %s with the error message %s.",
+                                    finalAction,
+                                    e.getMessage().replaceAll("\\n", "\n")
+                                )
                         );
                 });
                 if (tools.get(action) instanceof MLModelTool) {

ml-algorithms/src/main/java/org/opensearch/ml/engine/algorithms/agent/MLPlanExecuteAndReflectAgentRunner.java

@@ -520,6 +520,11 @@
             if (response.contains("```")) {
                 response = response.substring(0, response.lastIndexOf("```"));
             }
+        } else {
+            // extract content from {} block
+            if (response.contains("{") && response.contains("}")) {
+                response = response.substring(response.indexOf("{"), response.lastIndexOf("}") + 1);
+            }
         }
 
         response = response.trim();

ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/IndexMappingTool.java

@@ -95,7 +95,11 @@
         try {
             List<String> indexList = new ArrayList<>();
             if (StringUtils.isNotBlank(parameters.get("index"))) {
-                indexList = gson.fromJson(parameters.get("index"), List.class);
+                try {
+                    indexList = gson.fromJson(parameters.get("index"), List.class);
+                } catch (Exception e) {
+                    indexList.add(parameters.get("index"));
+                }
             }
 
             if (indexList.isEmpty()) {