fix(D-01): atomic snapshot for registry to prevent torn reads (BUG-001)

Replace two separate volatile fields (DEFINITIONS, COMPONENT_HOLDERS)
with a single RegistrySnapshot record swapped atomically. This prevents
race conditions where a reader thread could see new definitions paired
with stale/empty component holders between the two volatile writes.

src/main/java/com/tiedup/remake/v2/bondage/datadriven/DataDrivenItemRegistry.java

@@ -18,9 +18,9 @@ import org.jetbrains.annotations.Nullable;
  * Thread-safe registry for data-driven bondage item definitions.
  *
  * <p>Populated by the reload listener that scans {@code tiedup_items/} JSON files.
- * Uses volatile atomic swap (same pattern as {@link
- * com.tiedup.remake.client.animation.context.ContextGlbRegistry}) to ensure
- * the render thread always sees a consistent snapshot.</p>
+ * Uses a single volatile snapshot reference to ensure readers always see a
+ * consistent pair of definitions + component holders. This prevents torn reads
+ * where one map is updated but the other is stale.</p>
  *
  * <p>Lookup methods accept either a {@link ResourceLocation} ID directly
  * or an {@link ItemStack} (reads the {@code tiedup_item_id} NBT tag).</p>
@@ -31,20 +31,22 @@ public final class DataDrivenItemRegistry {
     public static final String NBT_ITEM_ID = "tiedup_item_id";
 
     /**
-     * Volatile reference to an unmodifiable map. Reload builds a new map
-     * and swaps atomically; consumer threads always see a consistent snapshot.
+     * Immutable snapshot combining definitions and their component holders.
+     * Swapped atomically via a single volatile write to prevent torn reads.
      */
-    private static volatile Map<
-        ResourceLocation,
-        DataDrivenItemDefinition
-    > DEFINITIONS = Map.of();
+    private record RegistrySnapshot(
+        Map<ResourceLocation, DataDrivenItemDefinition> definitions,
+        Map<ResourceLocation, ComponentHolder> holders
+    ) {
+        static final RegistrySnapshot EMPTY = new RegistrySnapshot(Map.of(), Map.of());
+    }
 
     /**
-     * Parallel cache of instantiated component holders, keyed by item definition ID.
-     * Rebuilt every time DEFINITIONS changes.
+     * Single volatile reference to the current registry state.
+     * All read methods capture this reference ONCE at the start to ensure
+     * consistency within a single call.
      */
-    private static volatile Map<ResourceLocation, ComponentHolder>
-        COMPONENT_HOLDERS = Map.of();
+    private static volatile RegistrySnapshot SNAPSHOT = RegistrySnapshot.EMPTY;
 
     private DataDrivenItemRegistry() {}
 
@@ -57,8 +59,9 @@ public final class DataDrivenItemRegistry {
     public static void reload(
         Map<ResourceLocation, DataDrivenItemDefinition> newDefs
     ) {
-        DEFINITIONS = Collections.unmodifiableMap(new HashMap<>(newDefs));
-        COMPONENT_HOLDERS = buildComponentHolders(DEFINITIONS);
+        Map<ResourceLocation, DataDrivenItemDefinition> defs =
+            Collections.unmodifiableMap(new HashMap<>(newDefs));
+        SNAPSHOT = new RegistrySnapshot(defs, buildComponentHolders(defs));
     }
 
     /**
@@ -67,7 +70,8 @@ public final class DataDrivenItemRegistry {
      * <p>On an integrated server, both the client (assets/) and server (data/) reload
      * listeners populate this registry. Using {@link #reload} would cause the second
      * listener to overwrite the first's definitions. This method builds a new map
-     * from the existing snapshot + the new entries, then swaps atomically.</p>
+     * from the existing snapshot + the new entries, then swaps atomically as a
+     * single snapshot to prevent torn reads.</p>
      *
      * @param newDefs the definitions to merge (will overwrite existing entries with same key)
      */
@@ -75,11 +79,12 @@ public final class DataDrivenItemRegistry {
         Map<ResourceLocation, DataDrivenItemDefinition> newDefs
     ) {
         Map<ResourceLocation, DataDrivenItemDefinition> merged = new HashMap<>(
-            DEFINITIONS
+            SNAPSHOT.definitions
         );
         merged.putAll(newDefs);
-        DEFINITIONS = Collections.unmodifiableMap(merged);
-        COMPONENT_HOLDERS = buildComponentHolders(DEFINITIONS);
+        Map<ResourceLocation, DataDrivenItemDefinition> defs =
+            Collections.unmodifiableMap(merged);
+        SNAPSHOT = new RegistrySnapshot(defs, buildComponentHolders(defs));
     }
 
     /**
@@ -90,7 +95,7 @@ public final class DataDrivenItemRegistry {
      */
     @Nullable
     public static DataDrivenItemDefinition get(ResourceLocation id) {
-        return DEFINITIONS.get(id);
+        return SNAPSHOT.definitions.get(id);
     }
 
     /**
@@ -108,7 +113,7 @@ public final class DataDrivenItemRegistry {
             tag.getString(NBT_ITEM_ID)
         );
         if (id == null) return null;
-        return DEFINITIONS.get(id);
+        return SNAPSHOT.definitions.get(id);
     }
 
     /**
@@ -117,15 +122,14 @@ public final class DataDrivenItemRegistry {
      * @return unmodifiable collection of all definitions
      */
     public static Collection<DataDrivenItemDefinition> getAll() {
-        return DEFINITIONS.values();
+        return SNAPSHOT.definitions.values();
     }
 
     /**
      * Clear all definitions. Called on world unload or for testing.
      */
     public static void clear() {
-        DEFINITIONS = Map.of();
-        COMPONENT_HOLDERS = Map.of();
+        SNAPSHOT = RegistrySnapshot.EMPTY;
     }
 
     // ===== COMPONENT HOLDERS =====
@@ -133,14 +137,27 @@ public final class DataDrivenItemRegistry {
     /**
      * Get the ComponentHolder for a data-driven item stack.
      *
+     * <p>Captures the snapshot reference once to ensure consistent reads
+     * between the definition lookup and the holder lookup.</p>
+     *
      * @param stack the ItemStack to inspect
      * @return the holder, or null if the stack is not data-driven or has no definition
      */
     @Nullable
     public static ComponentHolder getComponents(ItemStack stack) {
-        DataDrivenItemDefinition def = get(stack);
+        if (stack.isEmpty()) return null;
+        CompoundTag tag = stack.getTag();
+        if (tag == null || !tag.contains(NBT_ITEM_ID)) return null;
+        ResourceLocation id = ResourceLocation.tryParse(
+            tag.getString(NBT_ITEM_ID)
+        );
+        if (id == null) return null;
+        // Capture snapshot once to ensure definition and holder come from
+        // the same atomic snapshot, preventing torn reads.
+        RegistrySnapshot snap = SNAPSHOT;
+        DataDrivenItemDefinition def = snap.definitions.get(id);
         if (def == null) return null;
-        return COMPONENT_HOLDERS.get(def.id());
+        return snap.holders.get(def.id());
     }
 
     /**
@@ -151,7 +168,7 @@ public final class DataDrivenItemRegistry {
      */
     @Nullable
     public static ComponentHolder getComponents(ResourceLocation id) {
-        return COMPONENT_HOLDERS.get(id);
+        return SNAPSHOT.holders.get(id);
     }
 
     /**