Register inventory tabs from the client proxy, not the mod class

Deferring registration to loadComplete is right - TConstruct needs to have
registered first - but naming TabRegistry and the tab classes in CustomNpcs put
client-only GUI types in a class the server loads, which the verifier resolves
at link time regardless of any runtime side check. A proxy hook keeps them in
ClientProxy while still running at the same point.

src/main/java/noppes/npcs/CommonProxy.java

@@ -225,6 +225,14 @@ public class CommonProxy implements IGuiHandler {
     public void buildPackageIndex() {
     }
 
+    /**
+     * Called from the mod's FMLLoadCompleteEvent, after every other mod has finished loading.
+     * Anything that has to observe another mod's registrations belongs here rather than in
+     * load(), and it stays on the proxy so client-only types never reach the server.
+     */
+    public void loadComplete() {
+    }
+
     public boolean isScriptingEnabled() {
         return ConfigScript.ScriptingEnabled;
     }

src/main/java/noppes/npcs/CustomNpcs.java

@@ -64,7 +64,6 @@ import nikedemos.markovnames.generators.MarkovSlavic;
 import nikedemos.markovnames.generators.MarkovSpanish;
 import nikedemos.markovnames.generators.MarkovWelsh;
 import noppes.npcs.compat.PixelmonHelper;
-import noppes.npcs.config.ConfigClient;
 import noppes.npcs.config.ConfigMain;
 import noppes.npcs.config.LoadConfiguration;
 import noppes.npcs.config.legacy.LegacyConfig;
@@ -120,9 +119,6 @@ import noppes.npcs.entity.old.EntityNpcNagaMale;
 import noppes.npcs.entity.old.EntityNpcSkeleton;
 import noppes.npcs.scripted.NpcAPI;
 import somehussar.janino.AdvancedClassFilter;
-import tconstruct.client.tabs.InventoryTabCustomNpc;
-import tconstruct.client.tabs.InventoryTabVanilla;
-import tconstruct.client.tabs.TabRegistry;
 
 import java.io.File;
 import java.util.HashSet;
@@ -347,15 +343,10 @@ public class CustomNpcs {
 
     @EventHandler
     public void loadComplete(FMLLoadCompleteEvent ev) {
-        if (ev.getSide().isClient()) {
-            if (ConfigClient.InventoryGuiEnabled) {
-                MinecraftForge.EVENT_BUS.register(new TabRegistry());
-                if (TabRegistry.getTabList().isEmpty()) {
-                    TabRegistry.registerTab(new InventoryTabVanilla());
-                }
-                TabRegistry.registerTab(new InventoryTabCustomNpc());
-            }
-        }
+        // Runs after every other mod has loaded. Kept on the proxy: the client side registers
+        // inventory tabs, and naming those types here would drag client-only GUI classes into
+        // a class the server loads.
+        proxy.loadComplete();
         proxy.buildPackageIndex();
 
         // Load built-in animations on the client so they're available for ability preview.

src/main/java/noppes/npcs/client/ClientProxy.java

@@ -854,6 +854,19 @@ public class ClientProxy extends CommonProxy {
         return Minecraft.getMinecraft().currentScreen != null;
     }
 
+    @Override
+    public void loadComplete() {
+        // Deferred from load() so TConstruct has registered its own tabs first - registering
+        // ours before it left the vanilla tab duplicated.
+        if (ConfigClient.InventoryGuiEnabled) {
+            MinecraftForge.EVENT_BUS.register(new TabRegistry());
+            if (TabRegistry.getTabList().isEmpty()) {
+                TabRegistry.registerTab(new InventoryTabVanilla());
+            }
+            TabRegistry.registerTab(new InventoryTabCustomNpc());
+        }
+    }
+
     public void buildPackageIndex() {
         try {
             PackageFinder.init(Thread.currentThread().getContextClassLoader());