optimize visibility calcs

src/world/generation/terrain.rs

@@ -146,8 +146,18 @@ pub fn generate_chunk_terrain(
         });
     });
 
-    for (pos, data) in tilemap_updates.into_inner().unwrap() {
-        tilemap.floor_tiles.insert(pos, data);
+    let new_positions: Vec<IVec3> = tilemap_updates
+        .into_inner()
+        .unwrap()
+        .into_iter()
+        .map(|(pos, data)| {
+            tilemap.floor_tiles.insert(pos, data);
+            pos
+        })
+        .collect();
+
+    // All tiles now in tilemap — safe to calculate visibility
+    for pos in new_positions {
         occlusion_event_writer.write(TileOcclusionEvent { tile_position: pos });
     }