per-mesh 引用：MeshRendererComponent.meshIndex（-1=整模型）贯穿渲染收集/物理 Mesh 碰撞（自动跟随）/场景序列化（缺省键向前兼容）/Inspector mesh 下拉

Engine/src/Physics/PhysicsWorld.cpp

@@ -767,8 +767,14 @@ namespace Engine {
         // 动态/运动体 → ConvexHull（MeshShape 三角网格太贵，Jolt 不允许动）
         if (rb.type != ECS::RigidBodyComponent::BodyType::Static) {
             JPH::ConvexHullShapeSettings cs;
-            for (const auto &mesh: model->GetMeshes()) {
-                for (const auto &p: mesh->GetCpuPositions()) {
+            const auto &meshes = model->GetMeshes();
+            for (size_t mi = 0; mi < meshes.size(); ++mi) {
+                // 单 mesh 子引用：碰撞只取渲染可见的同一 mesh（语义跟随）
+                if (mc->meshIndex >= 0 &&
+                    static_cast<int>(mi) != mc->meshIndex) {
+                    continue;
+                }
+                for (const auto &p: meshes[mi]->GetCpuPositions()) {
                     cs.mPoints.emplace_back(p.x * s.x, p.y * s.y, p.z * s.z);
                 }
             }
@@ -788,9 +794,15 @@ namespace Engine {
         JPH::VertexList verts;
         JPH::IndexedTriangleList tris;
         u32 base = 0;
-        for (const auto &mesh: model->GetMeshes()) {
-            const auto &pos = mesh->GetCpuPositions();
-            const auto &idx = mesh->GetCpuIndices();
+        const auto &meshes = model->GetMeshes();
+        for (size_t mi = 0; mi < meshes.size(); ++mi) {
+            // 单 mesh 子引用：碰撞只取渲染可见的同一 mesh（语义跟随）
+            if (mc->meshIndex >= 0 &&
+                static_cast<int>(mi) != mc->meshIndex) {
+                continue;
+            }
+            const auto &pos = meshes[mi]->GetCpuPositions();
+            const auto &idx = meshes[mi]->GetCpuIndices();
             verts.reserve(verts.size() + pos.size());
             for (const auto &p: pos) {
                 verts.push_back(JPH::Float3(p.x * s.x, p.y * s.y, p.z * s.z));