fix(3d): Handle user_data meshes in visual debug wireframe rendering

- Check user_data before calling GetMeshAsset() in renderer_draw.cc
- Prevents crash when rendering manually loaded OBJ meshes with --debug
- Remove duplicate wireframe call in test_mesh.cc (now handled by renderer)
- Keep add_mesh_normals() call (not auto-handled by renderer)

Fixes: Bus error when running 'test_mesh house.obj --debug'
Root cause: GetMeshAsset(0) on non-asset meshes
Test: All 32 tests pass, test_mesh works with --debug flag

2 files changed, 25 insertions, 14 deletions

diff --git a/src/3d/renderer_draw.cc b/src/3d/renderer_draw.cc
index 7a95924..2b19787 100644
--- a/src/3d/renderer_draw.cc
+++ b/src/3d/renderer_draw.cc
@@ -1,9 +1,9 @@
 // This file is part of the 64k demo project.
 // It implements the drawing logic for Renderer3D.
 
+#include "3d/plane_data.h" // Include for PlaneData struct
 #include "3d/renderer.h"
 #include "util/asset_manager_utils.h"
-#include "3d/plane_data.h" // Include for PlaneData struct
 #include <algorithm>
 #include <vector>
 
@@ -59,11 +59,13 @@ void Renderer3D::update_uniforms(const Scene& scene, const Camera& camera,
 
     float plane_distance = 0.0f;
     if (obj.type == ObjectType::PLANE && obj.shared_user_data) {
-        // Safely cast shared_user_data to PlaneData* and get distance
-        plane_distance = static_cast<PlaneData*>(obj.shared_user_data.get())->distance;
+      // Safely cast shared_user_data to PlaneData* and get distance
+      plane_distance =
+          static_cast<PlaneData*>(obj.shared_user_data.get())->distance;
     }
 
-    data.params = vec4(type_id, plane_distance, obj.local_extent.x, obj.local_extent.y);
+    data.params =
+        vec4(type_id, plane_distance, obj.local_extent.x, obj.local_extent.y);
     obj_data.push_back(data);
     if (obj_data.size() >= kMaxObjects)
       break;
@@ -197,12 +199,25 @@ void Renderer3D::draw(WGPURenderPassEncoder pass, const Scene& scene,
       if (obj.type == ObjectType::TORUS) {
         extent = vec3(1.5f, 0.5f, 1.5f);
       } else if (obj.type == ObjectType::MESH) {
-        MeshAsset mesh = GetMeshAsset(obj.mesh_asset_id);
-        if (mesh.num_indices > 0) {
+        if (obj.user_data) {
+          // Manually loaded mesh (e.g., test_mesh tool)
+          struct MeshData {
+            std::vector<MeshVertex> vertices;
+            std::vector<uint32_t> indices;
+          };
+          auto* data = (MeshData*)obj.user_data;
           visual_debug_.add_mesh_wireframe(
-              obj.get_model_matrix(), mesh.num_vertices, mesh.vertices,
-              mesh.num_indices, mesh.indices,
-              vec3(0.0f, 1.0f, 1.0f)); // Cyan wireframe
+              obj.get_model_matrix(), (uint32_t)data->vertices.size(),
+              data->vertices.data(), (uint32_t)data->indices.size(),
+              data->indices.data(), vec3(0.0f, 1.0f, 1.0f)); // Cyan wireframe
+        } else {
+          MeshAsset mesh = GetMeshAsset(obj.mesh_asset_id);
+          if (mesh.num_indices > 0) {
+            visual_debug_.add_mesh_wireframe(
+                obj.get_model_matrix(), mesh.num_vertices, mesh.vertices,
+                mesh.num_indices, mesh.indices,
+                vec3(0.0f, 1.0f, 1.0f)); // Cyan wireframe
+          }
         }
       } else {
         extent = vec3(1.0f, 1.0f, 1.0f);
diff --git a/src/tests/test_mesh.cc b/src/tests/test_mesh.cc
index 0865f80..2129bc8 100644
--- a/src/tests/test_mesh.cc
+++ b/src/tests/test_mesh.cc
@@ -386,11 +386,7 @@ int main(int argc, char** argv) {
       dbg.add_mesh_normals(g_scene.objects[1].get_model_matrix(),
                            (uint32_t)data->vertices.size(),
                            data->vertices.data());
-      dbg.add_mesh_wireframe(g_scene.objects[1].get_model_matrix(),
-                             (uint32_t)data->vertices.size(),
-                             data->vertices.data(),
-                             (uint32_t)data->indices.size(),
-                             data->indices.data(), vec3(0.0f, 1.0f, 1.0f));
+      // Wireframe is now handled automatically by renderer
     }
 #endif /* !defined(STRIP_ALL) */