/data modify Causes Syncable Data Attachments to Desync

[Coder2195]

Miminal reproduction repo: https://github.com/Coder2195/data-attachment-desync-template-26.1

Directions, spawn allay, explore and modify data using data get and data modify

2026-03-26.16-16-29.mp4

[Coder2195]

I have a temp solution, which may contain bugs for whoever stumbles on this issue, but it works for me for most cases

@Mixin(Entity.class)
public abstract class EntityMixin implements ExtEntity, AttachmentTargetImpl {
	@SuppressWarnings("UnstableApiUsage")
	@WrapMethod(method = "load")
	private void bugFixFabricAttachmentSync(ValueInput input, Operation<Void> original) {
		if (!fabric_shouldTryToSync()) {
			original.call(input);
			return;
		}

		var oldAttachments = this.fabric_getAttachments();
		oldAttachments = oldAttachments != null ? new HashMap<>(oldAttachments) : new HashMap<>();

		original.call(input);

		var newAttachments = this.fabric_getAttachments();
		newAttachments = newAttachments != null ? new HashMap<>(newAttachments) : new HashMap<>();

		var allKeys = new HashSet<>(oldAttachments.keySet());
		allKeys.addAll(newAttachments.keySet());


		for (var key : allKeys) {
			var newValue = newAttachments.get(key);
			if (!key.isSynced() || newValue != null && newValue.equals(oldAttachments.get(key))) continue;

			AttachmentChange change = AttachmentChange.create(fabric_getSyncTargetInfo(), key, newValue, fabric_getRegistryAccess());
			this.fabric_syncChange(key, change);
		}
	}
}