use area instead of floor during map construction

src/ProxySession.hh

@@ -53,9 +53,11 @@ struct ProxySession {
   std::shared_ptr<std::string> quest_dat_data;
   std::shared_ptr<ItemCreator> item_creator;
   std::shared_ptr<MapState> map_state;
-  // TODO: Be less lazy and track item IDs correctly in proxy games. (Then
-  // change this to use the actual client's next item ID, not this hardcoded
-  // default.)
+  std::shared_ptr<const std::string> last_bin_contents;
+  std::shared_ptr<const std::string> last_dat_contents;
+  // Note: We intentionally don't use the client's item ID space because the
+  // client may create items at the same time as the proxy, so server/client
+  // state could go out of sync
   uint32_t next_item_id = 0x44000000;
 
   struct PersistentConfig {