fix: move client-only mixins to client array — fixes dedicated server crash (#28)

common/src/main/java/com/player2/playerengine/mixins/MixinEventFactoryEventImpl.java

@@ -0,0 +1,63 @@
+package com.player2.playerengine.mixins;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.ListIterator;
+import java.util.function.Function;
+
+/**
+ * Fixes ConcurrentModificationException in Architectury EventFactory.
+ *
+ * Architectury API issue #653: EventFactory uses a plain ArrayList for event
+ * listeners, which is not thread-safe. When a mod registers a listener during
+ * event dispatch (e.g., during the first server tick), the iterator throws
+ * ConcurrentModificationException.
+ *
+ * This mixin replaces the ArrayList with a SnapshotArrayList subclass that
+ * returns snapshot-based iterators, making concurrent registration during
+ * iteration safe. We must extend ArrayList because the field type is ArrayList,
+ * not List.
+ */
+@Mixin(targets = "dev.architectury.event.EventFactory$EventImpl", remap = false)
+public class MixinEventFactoryEventImpl<T> {
+
+    @Shadow
+    private ArrayList<T> listeners;
+
+    /**
+     * An ArrayList subclass whose iterators operate on a snapshot of the backing
+     * array at the time of iterator creation. This means concurrent add/remove
+     * during iteration won't throw ConcurrentModificationException.
+     */
+    public static class SnapshotArrayList<E> extends ArrayList<E> {
+        @Override
+        public Iterator<E> iterator() {
+            // Return an iterator over a snapshot copy
+            return new ArrayList<>(this).iterator();
+        }
+
+        @Override
+        public ListIterator<E> listIterator() {
+            return new ArrayList<>(this).listIterator();
+        }
+
+        @Override
+        public ListIterator<E> listIterator(int index) {
+            return new ArrayList<>(this).listIterator(index);
+        }
+    }
+
+    @Inject(method = "<init>", at = @At("RETURN"))
+    private void playerengine$replaceListenersWithSnapshotList(Function<?, ?> function, CallbackInfo ci) {
+        // Replace the plain ArrayList with our SnapshotArrayList.
+        // The snapshot iterator pattern means that iteration (event dispatch) sees
+        // a frozen copy, while registration can safely modify the real list.
+        this.listeners = new SnapshotArrayList<>();
+    }
+}

common/src/main/java/com/player2/playerengine/mixins/baritone/MixinItemStack.java

@@ -19,11 +19,39 @@ public abstract class MixinItemStack implements IItemStack {
    @Unique
    private int baritoneHash;
 
+   // Thread-local recursion guard: prevents infinite loop when getDamageValue()
+   // triggers ItemStack.copy -> ItemStack.<init> -> recalculateHash -> getDamageValue
+   // (e.g. Silent Gear MainPartItem.getMaxDamage -> PartInstance -> ItemStack.copy)
+   @Unique
+   private static final ThreadLocal<Boolean> playerengine$inRecalc = ThreadLocal.withInitial(() -> Boolean.FALSE);
+
    @Shadow
    public abstract int getDamageValue();
 
    private void recalculateHash() {
-      this.baritoneHash = this.item == null ? -1 : this.item.hashCode() + this.getDamageValue();
+      if (this.item == null) {
+         this.baritoneHash = -1;
+         return;
+      }
+      // If we're already inside recalculateHash on this thread, skip to avoid recursion.
+      // This breaks the cycle: recalculateHash -> getDamageValue -> getMaxDamage ->
+      // PartInstance -> ItemStack.copy -> ItemStack.<init> -> recalculateHash
+      if (playerengine$inRecalc.get()) {
+         this.baritoneHash = this.item.hashCode();
+         return;
+      }
+      playerengine$inRecalc.set(Boolean.TRUE);
+      try {
+         this.baritoneHash = this.item.hashCode() + this.getDamageValue();
+      } catch (Throwable t) {
+         // Catches failure modes during ItemStack init:
+         // - IllegalStateException: NeoForge config not loaded (e.g. ConstructionStick)
+         // - RuntimeException: client-only class loaded on DEDICATED_SERVER
+         // - StackOverflowError: any remaining deep recursion
+         this.baritoneHash = this.item.hashCode();
+      } finally {
+         playerengine$inRecalc.set(Boolean.FALSE);
+      }
    }
 
    @Inject(

common/src/main/resources/playerengine.mixins.json

@@ -8,15 +8,16 @@
     "defaultRequire": 1
   },
   "client": [
+    "ClientBlockBreakMixin",
+    "PlayerCollidesWithEntityMixin"
   ],
   "mixins": [
-    "ClientBlockBreakMixin",
     "ClientConnectionAccessor",
     "EntityAnimationSwungMixin",
     "LivingEntityMixin",
     "MixinAbstractFurnaceBlockEntity",
+    "MixinEventFactoryEventImpl",
     "PersistentProjectileEntityAccessor",
-    "PlayerCollidesWithEntityMixin",
     "PlayerDamageMixin",
     "WorldBlockModifiedMixin",
     "baritone.MixinBucketItem",
@@ -28,4 +29,4 @@
     "baritone.MixinServerCommandSource",
     "baritone.MixinUtil"
   ]
-}
+}