diff --git a/src/data/dto/NavDto.cpp b/src/data/dto/NavDto.cpp
index 2241804..e4a45f2 100644
--- a/src/data/dto/NavDto.cpp
+++ b/src/data/dto/NavDto.cpp
@@ -91,13 +91,17 @@ std::vector<StructTreeNode> buildStructTree(const std::vector<StructNode>& flat)
     auto isRootLevel = [&](const StructNode& n) {
         return n.parentId.empty() || ids.find(n.parentId) == ids.end();
     };
+    // visited 防环：每个 id 最多进树一次。对正常树（单父）等价于原逻辑；
+    // 对不可信后端数据的多节点环 / 重复 id 环，避免无限递归（规约：永不信任外部数据）。
+    std::set<std::string> visited;
     std::function<std::vector<StructTreeNode>(const std::string&, bool)> build =
         [&](const std::string& parentId, bool root) {
             std::vector<StructTreeNode> out;
             for (const auto& n : flat) {
                 const bool belongs = root ? isRootLevel(n) : (n.parentId == parentId);
                 if (!belongs) continue;
-                if (n.id == parentId) continue;  // 防自环
+                if (visited.count(n.id)) continue;  // 已进树 → 跳过，防环/防重复
+                visited.insert(n.id);
                 StructTreeNode t;
                 t.node = n;
                 t.isTm = isLeaf(n.id);
diff --git a/tests/data/test_nav_dto.cpp b/tests/data/test_nav_dto.cpp
index 878901f..e7e4368 100644
--- a/tests/data/test_nav_dto.cpp
+++ b/tests/data/test_nav_dto.cpp
@@ -106,3 +106,16 @@ TEST(NavDto, BuildStructTreeOrphanParentBecomesRoot) {
 TEST(NavDto, BuildStructTreeEmpty) {
     EXPECT_TRUE(dto::buildStructTree({}).empty());
 }
+
+TEST(NavDto, BuildStructTreeHandlesCycleWithoutInfiniteRecursion) {
+    // 不可信数据：重复 id 形成可达环（R→X→Y→重复X…）。必须终止、不崩。
+    const std::vector<StructNode> flat = {
+        {"R", "根", "",  "GS", "", 1},
+        {"X", "x",  "R", "GS", "", 1},
+        {"Y", "y",  "X", "GS", "", 1},
+        {"X", "x2", "Y", "TM", "", 2},  // 重复 id X，父=Y → 若不防环将无限递归
+    };
+    const auto roots = dto::buildStructTree(flat);  // 不挂起即通过
+    ASSERT_EQ(roots.size(), 1u);
+    EXPECT_EQ(roots[0].node.id, "R");
+}