fix: updable to get update-time when forgot the message (#17395)

### Summary

As title

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

internal/engine/elasticsearch/chunk.go

@@ -413,6 +413,7 @@ func (e *elasticsearchEngine) updateSingleMemoryMessage(ctx context.Context, ind
 		Index:      indexName,
 		DocumentID: messageDocID,
 		Body:       bytes.NewReader(body),
+		Refresh:    "wait_for",
 	}
 	res, err := req.Do(ctx, e.client)
 	if err != nil {

internal/engine/elasticsearch/chunk_helpers_test.go

@@ -1,10 +1,15 @@
 package elasticsearch
 
 import (
+	"context"
+	"net/http"
+	"net/http/httptest"
 	"reflect"
 	"strings"
 	"testing"
 
+	"github.com/elastic/go-elasticsearch/v8"
+
 	"ragflow/internal/engine/types"
 )
 
@@ -35,6 +40,37 @@ func TestBuildQueryStringQueryKeepsDocumentFieldsUnchanged(t *testing.T) {
 	assertEqual(t, queryString["fields"], []string{"name^10"})
 }
 
+func TestUpdateSingleMemoryMessageWaitsForRefresh(t *testing.T) {
+	var gotRefresh string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/memory_tenant/_update/memory-1_42" {
+			t.Errorf("path=%s, want /memory_tenant/_update/memory-1_42", r.URL.Path)
+			http.Error(w, "unexpected request path", http.StatusNotFound)
+			return
+		}
+		gotRefresh = r.URL.Query().Get("refresh")
+		w.Header().Set("X-Elastic-Product", "Elasticsearch")
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"result":"updated"}`))
+	}))
+	defer server.Close()
+
+	client, err := elasticsearch.NewClient(elasticsearch.Config{
+		Addresses: []string{server.URL},
+	})
+	if err != nil {
+		t.Fatalf("new elasticsearch client: %v", err)
+	}
+
+	engine := &elasticsearchEngine{client: client}
+	if err := engine.updateSingleMemoryMessage(context.Background(), "memory_tenant", "memory-1_42", map[string]interface{}{"forget_at": "2026-07-27 10:00:00"}); err != nil {
+		t.Fatalf("updateSingleMemoryMessage: %v", err)
+	}
+	if gotRefresh != "wait_for" {
+		t.Fatalf("refresh=%q, want wait_for", gotRefresh)
+	}
+}
+
 func TestElasticsearchGetFieldsFiltersAndUsesIDFallback(t *testing.T) {
 	engine := &elasticsearchEngine{}
 	chunks := []map[string]interface{}{