diff --git a/frontend/src/app/components/viewer3d.tsx b/frontend/src/app/components/viewer3d.tsx
index 6c730ed9..67189bc1 100644
--- a/frontend/src/app/components/viewer3d.tsx
+++ b/frontend/src/app/components/viewer3d.tsx
@@ -1,6 +1,6 @@
 'use client';
 
-import React, { Suspense, useMemo } from 'react';
+import React, { Suspense, useEffect, useMemo } from 'react';
 import { Canvas } from '@react-three/fiber';
 import { Environment, OrbitControls, useGLTF } from '@react-three/drei';
 
@@ -8,6 +8,12 @@ type Viewer3DProps = {
   modelUrl: string;
 };
 
+declare global {
+  interface Window {
+    __lod0VisibleAt?: number;
+  }
+}
+
 function Model({ modelUrl }: { modelUrl: string }) {
   // Resolve absolute URL to avoid base path issues
   const src = useMemo(() => {
@@ -19,6 +25,33 @@ function Model({ modelUrl }: { modelUrl: string }) {
 
   // Load GLB (no extra params to avoid signature mismatches)
   const gltf = useGLTF(src);
+
+  useEffect(() => {
+    if (typeof window === 'undefined') {
+      return undefined;
+    }
+
+    if (!gltf?.scene) {
+      return undefined;
+    }
+
+    let cancelled = false;
+    const rafId = window.requestAnimationFrame(() => {
+      if (cancelled) {
+        return;
+      }
+
+      const ts = performance.now();
+      window.__lod0VisibleAt = ts;
+      window.dispatchEvent(new CustomEvent('lod0:visible', { detail: { ts } }));
+    });
+
+    return () => {
+      cancelled = true;
+      window.cancelAnimationFrame(rafId);
+    };
+  }, [gltf?.scene, src]);
+
   return <primitive object={gltf.scene} />;
 }