fix: harden rag answerability gate

internal/ai/runtime/internal/impl/callbacks/runlog_callback.go

@@ -106,6 +106,15 @@ func (c *RuntimeTraceCollector) SetRetrieverSummary(summary RetrieverTraceSummar
 	c.Data.Retriever.Policies = append([]RetrieverPolicyTraceItem(nil), summary.Policies...)
 }
 
+func (c *RuntimeTraceCollector) AddRetrieverItems(items []RetrieverTraceItem) {
+	if len(items) == 0 {
+		return
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.Data.Retriever.Items = append(c.Data.Retriever.Items, items...)
+}
+
 func (c *RuntimeTraceCollector) SetAnswerability(data AnswerabilityTraceData) {
 	c.mu.Lock()
 	defer c.mu.Unlock()

internal/ai/runtime/internal/impl/callbacks/runlog_callback_test.go

@@ -0,0 +1,20 @@
+package callbacks
+
+import "testing"
+
+func TestRuntimeTraceCollectorAddRetrieverItems(t *testing.T) {
+	collector := NewRuntimeTraceCollector()
+
+	collector.AddRetrieverItems([]RetrieverTraceItem{
+		{KnowledgeBaseID: 1, DocumentID: 10, DocumentTitle: "doc-1"},
+		{KnowledgeBaseID: 2, DocumentID: 20, DocumentTitle: "doc-2"},
+	})
+	collector.AddRetrieverItems(nil)
+
+	if got := len(collector.Data.Retriever.Items); got != 2 {
+		t.Fatalf("expected two retriever items, got %d", got)
+	}
+	if collector.Data.Retriever.Items[0].DocumentTitle != "doc-1" || collector.Data.Retriever.Items[1].DocumentTitle != "doc-2" {
+		t.Fatalf("unexpected retriever items: %#v", collector.Data.Retriever.Items)
+	}
+}