Fixes multiblock rendering issues on world load (#4302)

Author: Saereth

src/main/java/com/gregtechceu/gtceu/api/machine/MetaMachine.java

@@ -228,6 +228,12 @@ public void onLoad() {
                 this.isPainted() != renderState.getValue(GTMachineModelProperties.IS_PAINTED)) {
             setRenderState(renderState.setValue(GTMachineModelProperties.IS_PAINTED, this.isPainted()));
         }
+
+        // Force model data refresh on client when BlockEntity finishes loading,
+        // in case the chunk was rendered before this BlockEntity was available
+        if (isRemote()) {
+            scheduleRenderUpdate();
+        }
     }
 
     /**

src/main/java/com/gregtechceu/gtceu/api/machine/multiblock/part/MultiblockPartMachine.java

@@ -12,6 +12,7 @@
 import com.gregtechceu.gtceu.client.model.machine.MachineRenderState;
 
 import com.lowdragmc.lowdraglib.syncdata.annotation.DescSynced;
+import com.lowdragmc.lowdraglib.syncdata.annotation.RequireRerender;
 import com.lowdragmc.lowdraglib.syncdata.annotation.UpdateListener;
 import com.lowdragmc.lowdraglib.syncdata.field.ManagedFieldHolder;
 
@@ -38,6 +39,7 @@ public class MultiblockPartMachine extends MetaMachine implements IMultiPart {
             MetaMachine.MANAGED_FIELD_HOLDER);
 
     @DescSynced
+    @RequireRerender
     @UpdateListener(methodName = "onControllersUpdated")
     protected final Set<BlockPos> controllerPositions = new ObjectOpenHashSet<>(8);
     protected final SortedSet<IMultiController> controllers = new ReferenceLinkedOpenHashSet<>(8);

src/main/java/com/gregtechceu/gtceu/client/model/machine/multipart/MultiPartBakedModel.java

@@ -122,7 +122,9 @@ public ChunkRenderTypeSet getRenderTypes(BlockState state, RandomSource rand, Mo
         BlockPos pos = modelData.get(MODEL_DATA_POS);
 
         var machine = (level == null || pos == null) ? null : MetaMachine.getMachine(level, pos);
-        if (machine == null) return IDynamicBakedModel.super.getRenderTypes(state, rand, modelData);
+        // When machine is null (BE not loaded yet), use the default model's render types
+        // to ensure we still render something instead of being invisible
+        if (machine == null) return defaultModel.getRenderTypes(state, rand, modelData);
 
         var renderTypeSets = new LinkedList<ChunkRenderTypeSet>();
         var selectors = getSelectors(machine.getRenderState());