fix enqueueWork's logic

src/main/java/com/simibubi/create/foundation/mixin/fabric/BlockableEventLoopAccessor.java

@@ -0,0 +1,14 @@
+package com.simibubi.create.foundation.mixin.fabric;
+
+import java.util.concurrent.CompletableFuture;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Invoker;
+
+import net.minecraft.util.thread.BlockableEventLoop;
+
+@Mixin(BlockableEventLoop.class)
+public interface BlockableEventLoopAccessor {
+	@Invoker
+	CompletableFuture<Void> callSubmitAsync(Runnable task);
+}

src/main/java/com/simibubi/create/foundation/networking/SimplePacketBase.java

@@ -1,6 +1,6 @@
 package com.simibubi.create.foundation.networking;
 
-import java.util.concurrent.Executor;
+import com.simibubi.create.foundation.mixin.fabric.BlockableEventLoopAccessor;
 
 import org.jetbrains.annotations.Nullable;
 
@@ -15,6 +15,7 @@
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.server.network.ServerGamePacketListenerImpl;
+import net.minecraft.util.thread.BlockableEventLoop;
 
 public abstract class SimplePacketBase implements C2SPacket, S2CPacket {
 
@@ -42,9 +43,16 @@ public enum NetworkDirection {
 		PLAY_TO_SERVER
 	}
 
-	public record Context(Executor exec, PacketListener listener, @Nullable ServerPlayer sender) {
+	public record Context(BlockableEventLoop<? extends Runnable> executor, PacketListener listener, @Nullable ServerPlayer sender) {
 		public void enqueueWork(Runnable runnable) {
-			exec().execute(runnable);
+			// Matches Forge's enqueueWork behavior.
+			// MC will sometimes defer tasks even if already on the right thread.
+			if (executor.isSameThread()) {
+				runnable.run();
+			} else {
+				// skip extra checks
+				((BlockableEventLoopAccessor) executor).callSubmitAsync(runnable);
+			}
 		}
 
 		@Nullable

src/main/resources/create.mixins.json

@@ -23,6 +23,7 @@
     "accessor.ServerLevelAccessor",
     "accessor.SystemReportAccessor",
     "fabric.AbstractMinecartMixin",
+    "fabric.BlockableEventLoopAccessor",
     "fabric.EntityMixin",
     "fabric.RegistryMixin",
     "fabric.ServerGamePacketListenerImplAccessor",