fix: simplify fallback reply handling in knowledge guard

internal/ai/runtime/executor/knowledge_guard.go

@@ -8,6 +8,7 @@ import (
 	"cs-agent/internal/pkg/enums"
 
 	"github.com/cloudwego/eino/schema"
+	"github.com/mlogclub/simple/common/strs"
 )
 
 type knowledgeGuardDecision struct {
@@ -53,14 +54,10 @@ func resolveKnowledgeFallbackReply(aiAgent models.AIAgent) string {
 
 func resolveKnowledgeHumanSupportFallback(aiAgent models.AIAgent) string {
 	base := strings.TrimSpace(resolveKnowledgeFallbackReply(aiAgent))
-	if base == "" {
+	if strs.IsBlank(base) {
 		base = "当前知识库暂无明确信息。"
 	}
-	suggestion := "建议你联系人工客服进一步确认。"
-	if strings.Contains(base, suggestion) {
-		return base
-	}
-	return strings.TrimSpace(base + " " + suggestion)
+	return base
 }
 
 func buildKnowledgeRuntimeInstruction(answerMode enums.KnowledgeAnswerMode, fallbackReply string) string {