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Attachments are not synced on player creation

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Description

1.21.x bug
Minecraft version

1.21.1

Describe the bug

When a new player is created, e.g. upon join, dimension change, or respawn, attachments are not synced. Attachments do sync properly when setAttached/removeAttached is called.

Steps to reproduce
  1. Create a fabric mod with the following mod initializer
@SuppressWarnings("UnstableApiUsage")
public class BugDemo implements ModInitializer {
	public static final String MOD_ID = "bugdemo";

	public static final Logger LOGGER = LoggerFactory.getLogger(MOD_ID);

	public static final AttachmentType<Unit> TEST = AttachmentRegistry.create(ResourceLocation.fromNamespaceAndPath(MOD_ID, "test"), builder -> builder
			.persistent(Unit.CODEC)
			.syncWith(StreamCodec.unit(Unit.INSTANCE), AttachmentSyncPredicate.targetOnly())
			.copyOnDeath()
	);

	@Override
	public void onInitialize() {
		UseItemCallback.EVENT.register((player, world, hand) -> {
			var stack = player.getItemInHand(hand);

			if (stack.is(Items.BLAZE_ROD)) {
				if (world.isClientSide()) return InteractionResultHolder.success(stack);

				player.setAttached(TEST, Unit.INSTANCE);

				return InteractionResultHolder.success(stack);
			}

			if (stack.is(Items.STICK)) {
                LOGGER.info(
                        "{} {} attachment",
                        world.isClientSide() ? "client" : "server",
                        player.hasAttached(TEST) ? "has" : "does not have"
                );
                return InteractionResultHolder.success(stack);
            }

			return InteractionResultHolder.pass(stack);
        });
	}
}
  1. Run the mod on fabric.
  2. Use the blaze rod to set the attachment.
  3. Recreate the player by relogging, respawning, or changing dimensions.
  4. Use the stick. The log will show
[17:06:29] [Render thread/INFO] (bugdemo) client has attachment
[17:06:29] [Server thread/INFO] (bugdemo) server has attachment
  1. Run the mod on neoforge with connector & ffapi.
  2. Repeat steps 3-5. The log will show
[17:13:56] [Render thread/INFO] [bugdemo/]: client does not have attachment
[17:13:56] [Server thread/INFO] [bugdemo/]: server has attachment
  1. Use the blaze rod to re-set the attachment, then use the stick. The log will show
[17:18:53] [Render thread/INFO] [bugdemo/]: client has attachment
[17:18:53] [Server thread/INFO] [bugdemo/]: server has attachment

The expected behavior is that when the player is recreated, the server and client will both see the attachment.

Logs

No response

Additional context

Possibly related to FFAPI 2.2.0 using neoforge api for attachment sync.

Dominant language
Java
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Avg merge
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Merged PRs (30d)
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