fix: continue agent flow on knowledge retrieval errors

internal/ai/runtime/executor/answerability_gate.go

@@ -180,7 +180,7 @@ func (g *KnowledgeAnswerabilityGate) retrieveKnowledge(ctx context.Context, stat
 	retrieveOptions.QueryPreview = preview(req.UserMessage.Content, 120)
 	result, err := retriever.RetrieveContextByOptions(ctx, retrieveOptions, query)
 	if err != nil {
-		state.FallbackReply = resolveKnowledgeHumanSupportFallback(req.AIAgent)
+		state.Decision = buildKnowledgeRetrievalErrorDecision(req.AIAgent, knowledgeIDs)
 		state.ErrorMessage = err.Error()
 		state.recordAnswerability(answerabilityStatusUnanswerable, "knowledge retrieval failed", err)
 		return state, nil

internal/ai/runtime/executor/answerability_gate_test.go

@@ -248,7 +248,7 @@ func TestKnowledgePolicyEvaluateSkipsRuntimeActionIntent(t *testing.T) {
 	}
 }
 
-func TestKnowledgePolicyEvaluateFallsBackOnRetrieverError(t *testing.T) {
+func TestKnowledgePolicyEvaluateInjectsRetrievalErrorInstructionWithoutFallback(t *testing.T) {
 	collector := callbacks.NewRuntimeTraceCollector()
 	gate := newTestKnowledgePolicyGate(&fakeKnowledgeContextRetriever{
 		knowledgeBaseIDs: []int64{1},
@@ -263,8 +263,14 @@ func TestKnowledgePolicyEvaluateFallsBackOnRetrieverError(t *testing.T) {
 		t.Fatalf("Evaluate returned error: %v", err)
 	}
 
-	if !strings.Contains(state.FallbackReply, "我暂时没有找到足够准确的信息") {
-		t.Fatalf("expected configured fallback on retrieval error, got %q", state.FallbackReply)
+	if state.FallbackReply != "" {
+		t.Fatalf("expected no direct fallback on retrieval error, got %q", state.FallbackReply)
+	}
+	if len(state.Decision.Instructions) != 1 {
+		t.Fatalf("expected one retrieval-error instruction, got %d", len(state.Decision.Instructions))
+	}
+	if !strings.Contains(state.Decision.Instructions[0].Content, "知识库检索暂时不可用") {
+		t.Fatalf("unexpected retrieval-error instruction: %q", state.Decision.Instructions[0].Content)
 	}
 	if collector.Data.Answerability.Status != answerabilityStatusUnanswerable {
 		t.Fatalf("unexpected status: %q", collector.Data.Answerability.Status)
@@ -273,3 +279,23 @@ func TestKnowledgePolicyEvaluateFallsBackOnRetrieverError(t *testing.T) {
 		t.Fatalf("unexpected reason: %q", collector.Data.Answerability.Reason)
 	}
 }
+
+func TestBuildRunMessagesContinuesAgentFlowWhenRetrievalFails(t *testing.T) {
+	summary := &RunResult{}
+	gate := newTestKnowledgePolicyGate(&fakeKnowledgeContextRetriever{
+		knowledgeBaseIDs: []int64{1},
+		err:              errors.New("vector store unavailable"),
+	})
+
+	messages := buildRunMessages(context.Background(), newKnowledgePolicyRunInput("你好", "1"), summary, nil, gate)
+
+	if summary.ReplyText != "" {
+		t.Fatalf("expected no early fallback reply, got %q", summary.ReplyText)
+	}
+	if !messagesContainContent(messages, "知识库检索暂时不可用") {
+		t.Fatalf("expected retrieval-error instruction in messages: %#v", messages)
+	}
+	if !messagesContainContent(messages, "你好") {
+		t.Fatalf("expected current user message to remain in messages: %#v", messages)
+	}
+}

internal/ai/runtime/executor/knowledge_guard.go

@@ -53,6 +53,19 @@ func buildKnowledgeNoContextDecision(aiAgent models.AIAgent, knowledgeBaseIDs []
 	}
 }
 
+func buildKnowledgeRetrievalErrorDecision(aiAgent models.AIAgent, knowledgeBaseIDs []int64) knowledgeGuardDecision {
+	if len(knowledgeBaseIDs) == 0 {
+		return knowledgeGuardDecision{}
+	}
+	instruction := buildKnowledgeRetrievalErrorInstruction(resolveKnowledgeFallbackReply(aiAgent))
+	if instruction == "" {
+		return knowledgeGuardDecision{}
+	}
+	return knowledgeGuardDecision{
+		Instructions: []*schema.Message{schema.SystemMessage(instruction)},
+	}
+}
+
 func resolveKnowledgeFallbackReply(aiAgent models.AIAgent) string {
 	if reply := strings.TrimSpace(aiAgent.FallbackMessage); reply != "" {
 		return reply
@@ -96,3 +109,16 @@ func buildKnowledgeNoContextInstruction(fallbackReply string) string {
 		"3. 如果用户询问业务事实、规则、价格、流程、配置、时效、承诺、售后、退款、权限或政策，不得编造答案，必须明确回复：" + fallbackReply + "\n" +
 		"4. 不得输出知识库未提供的具体事实、流程、承诺、价格、时效或政策。"
 }
+
+func buildKnowledgeRetrievalErrorInstruction(fallbackReply string) string {
+	fallbackReply = strings.TrimSpace(fallbackReply)
+	if fallbackReply == "" {
+		fallbackReply = "当前知识库暂无明确信息。"
+	}
+	return "知识库检索状态：知识库检索暂时不可用，当前没有可用的知识库资料。\n" +
+		"回复策略：\n" +
+		"1. 如果用户只是寒暄、问候、感谢、确认或结束语，可以自然、简短地回复，不要使用知识库兜底话术。\n" +
+		"2. 如果用户表达不清楚或缺少上下文，应追问具体场景、对象、报错信息或操作步骤。\n" +
+		"3. 如果用户询问业务事实、规则、价格、流程、配置、时效、承诺、售后、退款、权限或政策，不得编造答案，必须明确回复：" + fallbackReply + "\n" +
+		"4. 不得输出知识库未提供的具体事实、流程、承诺、价格、时效或政策。"
+}