diff --git a/internal/traceimpact/service_empty_lists_test.go b/internal/traceimpact/service_empty_lists_test.go
new file mode 100644
index 00000000..668ffe75
--- /dev/null
+++ b/internal/traceimpact/service_empty_lists_test.go
@@ -0,0 +1,38 @@
+package traceimpact
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+func TestListMethodsReturnEmptySlicesNotNil(t *testing.T) {
+	svc := NewService(nil)
+	ctx := context.Background()
+
+	items, err := svc.ListItems(ctx, 42)
+	if err != nil || items == nil {
+		t.Fatalf("ListItems items=%v err=%v", items, err)
+	}
+	index, err := svc.ListIndex(ctx, 42)
+	if err != nil || index == nil {
+		t.Fatalf("ListIndex index=%v err=%v", index, err)
+	}
+	marks, err := svc.ListOpenMarks(ctx, 42, "")
+	if err != nil || marks == nil {
+		t.Fatalf("ListOpenMarks marks=%v err=%v", marks, err)
+	}
+
+	raw, err := json.Marshal(map[string]any{
+		"items":         items,
+		"index":         index,
+		"recheck_marks": marks,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(string(raw), "null") {
+		t.Fatalf("empty lists encoded as JSON null: %s", raw)
+	}
+}
diff --git a/web/src/api/projectTrace.test.ts b/web/src/api/projectTrace.test.ts
new file mode 100644
index 00000000..8a1e3b94
--- /dev/null
+++ b/web/src/api/projectTrace.test.ts
@@ -0,0 +1,55 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { fetchProjectTrace } from './projectTrace';
+
+test('fetchProjectTrace turns null arrays into empty arrays', async () => {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () =>
+    new Response(
+      JSON.stringify({
+        items: null,
+        hidden_count: 2,
+        index: null,
+        recheck_marks: null,
+      }),
+      { status: 200, headers: { 'Content-Type': 'application/json' } },
+    );
+  try {
+    const view = await fetchProjectTrace(7);
+    assert.deepEqual(view.items, []);
+    assert.equal(view.hidden_count, 2);
+    assert.deepEqual(view.index, []);
+    assert.deepEqual(view.recheck_marks, []);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
+test('fetchProjectTrace keeps real arrays and rejects failed responses', async () => {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () =>
+    new Response(
+      JSON.stringify({
+        items: [{ id: 1, business_key: 'UR-1', kind: 'requirement' }],
+        hidden_count: 0,
+        index: [{ doc_id: 'doc-1', status: 'ready', item_count: 1 }],
+        recheck_marks: [],
+      }),
+      { status: 200, headers: { 'Content-Type': 'application/json' } },
+    );
+  try {
+    const view = await fetchProjectTrace(7);
+    assert.equal(view.items.length, 1);
+    assert.equal(view.index[0]?.doc_id, 'doc-1');
+    assert.deepEqual(view.recheck_marks, []);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+
+  globalThis.fetch = async () => new Response('nope', { status: 500 });
+  try {
+    await assert.rejects(() => fetchProjectTrace(7), /需求与影响加载失败: 500/);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});