Allow to draw produced-item icons in recipe dialog and game world

src/lib/config/ConfigLoader.cpp

@@ -421,6 +421,14 @@ RecipesConfig ConfigLoader::loadRecipes(const std::string& path)
         const toml::array& outputs = requireArray(mt["outputs"], file, elemPath + ".outputs");
         def.outputs = parseRecipeOutputs(outputs, file, elemPath + ".outputs");
 
+        // Optional icon item id (REQ-UI-RECIPE-ICON); defaults to the first output
+        // in the UI when unset. Not validated against known items here — a missing
+        // icon is not an error (REQ-UI-ITEM-ICON).
+        if (mt.contains("icon"))
+        {
+            def.icon = requireString(mt["icon"], file, elemPath + ".icon");
+        }
+
         cfg.recipes.push_back(std::move(def));
     }
 

src/lib/config/RecipesConfig.h

@@ -32,6 +32,10 @@ struct RecipeDef
     std::vector<RecipeIngredient> inputs;
     std::vector<RecipeOutput> outputs;
     double durationSeconds;
+    // Optional id of the item whose icon represents this recipe in the recipe-
+    // selection dialog (REQ-UI-RECIPE-ICON). When unset, the first output item is
+    // used. A missing icon file for that item is not an error (REQ-UI-ITEM-ICON).
+    std::optional<std::string> icon;
     // Assembler only. When true, this recipe is available from game start
     // regardless of the implicit item graph — used for base recipes that no
     // schematic's materials reach (e.g. building blocks). See REQ-LOCK-IMPLICIT.