diff --git a/src/pages/XRSession.tsx b/src/pages/XRSession.tsx
index 7abd1b7..436ad82 100644
--- a/src/pages/XRSession.tsx
+++ b/src/pages/XRSession.tsx
@@ -359,10 +359,11 @@ function XRSnapHandler() {
 // ─── XR Grid ───────────────────────────────────────────
 function XRGrid() {
   const showGrid = useModelStore((s) => s.showGrid);
+  const gridY = useModelStore((s) => s.gridY);
   if (!showGrid) return null;
   return (
     <Grid
-      position={[0, -0.09, 0]}
+      position={[0, gridY, 0]}
       infiniteGrid
       cellSize={0.01}
       sectionSize={0.1}
@@ -376,6 +377,36 @@ function XRGrid() {
   );
 }
 
+/** Auto-follow grid to model bottom when enabled. */
+function XRGridAutoFollower() {
+  const models = useModelStore((s) => s.models);
+  const { scene } = useThree();
+  useEffect(() => {
+    if (!useModelStore.getState().gridAutoFollow) return;
+    const id = setTimeout(() => {
+      if (!useModelStore.getState().gridAutoFollow) return;
+      const box = new THREE.Box3();
+      let has = false;
+      scene.traverse((obj) => {
+        if (obj instanceof THREE.Mesh && obj.geometry) {
+          if (obj.geometry instanceof THREE.SphereGeometry) return;
+          if (obj.geometry instanceof THREE.RingGeometry) return;
+          if (obj.userData.__edgeLine) return;
+          obj.updateWorldMatrix(true, false);
+          const b = new THREE.Box3().setFromObject(obj);
+          if (isFinite(b.min.y)) {
+            if (!has) { box.copy(b); has = true; }
+            else box.union(b);
+          }
+        }
+      });
+      if (has) useModelStore.setState({ gridY: box.min.y - 0.005 });
+    }, 150);
+    return () => clearTimeout(id);
+  }, [models, scene]);
+  return null;
+}
+
 // ImageTrackingAnchor removed — replaced by XRHitTestPlacement
 
 // ─── XRSession Page ────────────────────────────────────