feat(crafting): craft powder snow from snow and a bucket (#3)

README.md

@@ -1,6 +1,6 @@
 # Purpur Inventory Helper
 
-A Purpur 26.2 plugin with Sorting Sticks, automatic broken-tool replacement, alternative Dispenser/Cobweb recipes, and risky over-level enchantment combining in ordinary anvils.
+A Purpur 26.2 plugin with Sorting Sticks, automatic broken-tool replacement, alternative Dispenser/Cobweb recipes, Powder Snow crafting, and risky over-level enchantment combining in ordinary anvils.
 
 The approved behavior is specified in the [SoMC OKF wiki](https://git.garvis.dev/dmg/somc-okf/src/branch/main/projects/purpur-inventory-helper/index.md).
 
@@ -52,6 +52,22 @@ existing manual crafting and inventory behavior remain available.
 
 One ordinary Dropper + Tripwire Hook produces one ordinary Dispenser through a shapeless recipe in the recipe book's Redstone category. The alternative is universally discovered for online and joining players, supports native autofill and batch completion, and leaves Minecraft's Bow-based Dispenser recipe unchanged. If the alternative cannot register safely, existing Inventory Helper behavior remains available and discovery retries after a later successful registration.
 
+## Powder Snow recipe
+
+One ordinary Snow Block + empty Bucket produces one ordinary Powder Snow Bucket through a
+shapeless recipe in both the personal 2×2 and crafting-table 3×3 grids. All players discover it
+in the recipe book's `MISC` category after successful registration. Native autofill and ordinary
+or shift/batch crafting consume one Snow Block and one Bucket per output, with **no additional
+empty Bucket remainder**. The filled Bucket is unstackable; native output-space and cancellation
+rules remain authoritative. Placement, recovery and Powder Snow hazards are unchanged.
+
+The recipe owns only `spigotinventoryhelper:snow_powder_snow` and its discovery listener.
+Conflicts/failures withhold its discovery without disabling other features; discovery can retry
+on later joins and successful re-enable. Disable removes owned registration/listeners, not native
+recipe-book knowledge or unrelated recipes. Native automated tests cover both grids, actual
+registered events/packet completion, metadata/quantity conservation and failure boundaries;
+real-client visuals and live placement/recovery remain unperformed non-blocking follow-ups.
+
 ## Sorting inventories
 
 Hold an authentic Sorting Stick and right-click:

src/main/java/games/dmg/spigotinventoryhelper/PowderSnowRecipeRegistrar.java

@@ -0,0 +1,72 @@
+package games.dmg.spigotinventoryhelper;
+
+import java.util.List;
+import java.util.Objects;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Server;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.ShapelessRecipe;
+import org.bukkit.inventory.recipe.CraftingBookCategory;
+
+/** Independently owns the fixed Snow Block and empty Bucket conversion. */
+public final class PowderSnowRecipeRegistrar implements RecipeRegistrar {
+    private final NamespacedKey recipeKey;
+    private Server registeredServer;
+    private boolean owned;
+
+    public PowderSnowRecipeRegistrar(NamespacedKey recipeKey) {
+        this.recipeKey = Objects.requireNonNull(recipeKey, "recipeKey");
+    }
+
+    @Override
+    public boolean register(Server server) {
+        Objects.requireNonNull(server, "server");
+        if (owned) {
+            return true;
+        }
+        registeredServer = server;
+        if (server.getRecipe(recipeKey) != null) {
+            return false;
+        }
+        ShapelessRecipe recipe = new ShapelessRecipe(recipeKey, new ItemStack(Material.POWDER_SNOW_BUCKET));
+        recipe.addIngredient(Material.SNOW_BLOCK);
+        recipe.addIngredient(Material.BUCKET);
+        recipe.setCategory(CraftingBookCategory.MISC);
+        try {
+            owned = server.addRecipe(recipe);
+            return owned;
+        } catch (RuntimeException exception) {
+            try {
+                owned = server.getRecipe(recipeKey) != null;
+                unregister();
+            } catch (RuntimeException cleanupFailure) {
+                exception.addSuppressed(cleanupFailure);
+            }
+            throw exception;
+        }
+    }
+
+    @Override
+    public List<NamespacedKey> recipeKeys() {
+        return List.of(recipeKey);
+    }
+
+    @Override
+    public void unregister() {
+        if (!owned || registeredServer == null) {
+            return;
+        }
+        // A prior removal may have succeeded before its port threw. Retain ownership on
+        // failure, but let a later cleanup confirm absence instead of stranding the lifecycle.
+        if (!registeredServer.removeRecipe(recipeKey) && registeredServer.getRecipe(recipeKey) != null) {
+            throw new IllegalStateException("Could not remove owned recipe " + recipeKey);
+        }
+        owned = false;
+    }
+
+    @Override
+    public String description() {
+        return "Powder Snow crafting recipe";
+    }
+}

src/main/java/games/dmg/spigotinventoryhelper/SpigotInventoryHelperPlugin.java

@@ -69,8 +69,14 @@ public final class SpigotInventoryHelperPlugin extends JavaPlugin {
                 new CobwebRecipeRegistrar(new NamespacedKey(this, "string_cobweb")),
                 getLogger()
         );
+        RecipeLifecycle powderSnowRecipe = new RecipeLifecycle(
+                getServer(),
+                this,
+                new PowderSnowRecipeRegistrar(new NamespacedKey(this, "snow_powder_snow")),
+                getLogger()
+        );
         recipeLifecycles = new RecipeLifecycleGroup(
-                List.of(sortingRecipes, dispenserRecipe, cobwebRecipe));
+                List.of(sortingRecipes, dispenserRecipe, cobwebRecipe, powderSnowRecipe));
         recipeLifecycles.enableAll();
         InventorySortingService sorting = new InventorySortingService(new InventorySorter());
         getServer().getPluginManager().registerEvents(

src/nativeTest/java/games/dmg/spigotinventoryhelper/NativeCobwebPluginWiringTest.java

@@ -52,7 +52,7 @@ import org.junit.jupiter.api.io.TempDir;
 /** Real enable/disable callbacks using Bukkit's explicit initialization and existing native fixtures. */
 class NativeCobwebPluginWiringTest {
     private static final NamespacedKey COBWEB = key("string_cobweb");
-    private static final Set<NamespacedKey> EXISTING = Set.of(key("dropper_dispenser"),
+    private static final Set<NamespacedKey> EXISTING = Set.of(key("snow_powder_snow"), key("dropper_dispenser"),
             key("sorting_stick_recipe_chest"), key("sorting_stick_recipe_barrel"));
     private static final NamespacedKey VANILLA = new NamespacedKey("minecraft", "stick");
     private static Server previousServer;
@@ -72,7 +72,9 @@ class NativeCobwebPluginWiringTest {
     static void bootstrap() throws Exception {
         NativeRuntime.bootstrap();
         previousServer = Bukkit.getServer();
-        serverUnderTest = mock(Server.class);
+        // ProtocolLib derives CraftBukkit's package from this external server's concrete class.
+        serverUnderTest = mock(org.bukkit.craftbukkit.CraftServer.class,
+                org.mockito.Mockito.withSettings().mockMaker(org.mockito.MockMakers.INLINE));
         setServer(serverUnderTest);
     }
 
@@ -112,7 +114,7 @@ class NativeCobwebPluginWiringTest {
         commands = new SimpleCommandMap(serverUnderTest, new HashMap<>());
         when(serverUnderTest.getPluginCommand(any(String.class))).thenAnswer(invocation ->
                 commands.getCommand(invocation.getArgument(0)));
-        var scheduler = mock(org.bukkit.scheduler.BukkitScheduler.class);
+        var scheduler = mock(org.bukkit.craftbukkit.scheduler.CraftScheduler.class);
         when(serverUnderTest.getScheduler()).thenReturn(scheduler);
         when(scheduler.runTaskTimer(any(), any(Runnable.class),
                 org.mockito.ArgumentMatchers.anyLong(), org.mockito.ArgumentMatchers.anyLong()))

src/nativeTest/java/games/dmg/spigotinventoryhelper/NativePowderSnowBookTest.java

@@ -0,0 +1,187 @@
+package games.dmg.spigotinventoryhelper;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+import java.nio.file.Path;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+import net.minecraft.network.protocol.game.ClientboundRecipeBookAddPacket;
+import net.minecraft.stats.ServerRecipeBook;
+import net.minecraft.world.item.crafting.RecipeBookCategories;
+import net.minecraft.world.item.crafting.display.ShapelessCraftingRecipeDisplay;
+import net.minecraft.world.item.crafting.display.SlotDisplay;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.player.PlayerRecipeDiscoverEvent;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/** Real native book/display codecs and actual registered join handlers, not a set-based book fake. */
+class NativePowderSnowBookTest {
+    @TempDir Path directory;
+    private static final NamespacedKey KEY = NativePowderSnowRecipeTest.KEY;
+    private static final NamespacedKey VANILLA = new NamespacedKey("minecraft", "stick");
+
+    private static long addedEntries(List<net.minecraft.network.protocol.Packet<?>> packets) {
+        return packets.stream().filter(ClientboundRecipeBookAddPacket.class::isInstance)
+                .map(ClientboundRecipeBookAddPacket.class::cast).mapToLong(packet -> packet.entries().size()).sum();
+    }
+
+    private static boolean powderEntry(ClientboundRecipeBookAddPacket.Entry entry) {
+        return entry.contents().display().result() instanceof SlotDisplay.ItemStackSlotDisplay result
+                && result.stack().create().is(net.minecraft.world.item.Items.POWDER_SNOW_BUCKET);
+    }
+
+    private static void assertPackedEquals(ServerRecipeBook.Packed expected, ServerRecipeBook.Packed actual) {
+        assertEquals(ServerRecipeBook.Packed.CODEC.encodeStart(net.minecraft.nbt.NbtOps.INSTANCE, expected).getOrThrow(),
+                ServerRecipeBook.Packed.CODEC.encodeStart(net.minecraft.nbt.NbtOps.INSTANCE, actual).getOrThrow());
+    }
+
+    @Test
+    void onlineDiscoverySendsOrdinarySearchableMiscDisplayWithOneNotificationAndHighlight() throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, 2)) {
+            var recipe = f.powder().value();
+            assertEquals(RecipeBookCategories.CRAFTING_MISC, recipe.recipeBookCategory());
+            var display = assertInstanceOf(ShapelessCraftingRecipeDisplay.class, recipe.display().getFirst());
+            var context = new net.minecraft.util.context.ContextMap.Builder()
+                    .withParameter(net.minecraft.world.item.crafting.display.SlotDisplayContext.REGISTRIES,
+                            org.bukkit.craftbukkit.CraftRegistry.getMinecraftRegistry())
+                    .create(net.minecraft.world.item.crafting.display.SlotDisplayContext.CONTEXT);
+            var ingredients = display.ingredients().stream().map(slot -> slot.resolveForStacks(context)).toList();
+            assertEquals(List.of(1, 1), ingredients.stream().map(List::size).toList());
+            assertEquals(List.of(Material.SNOW_BLOCK, Material.BUCKET), ingredients.stream()
+                    .map(items -> CraftItemStack.asBukkitCopy(items.getFirst()).getType()).toList());
+            var result = assertInstanceOf(SlotDisplay.ItemStackSlotDisplay.class, display.result()).stack().create();
+            assertEquals(Material.POWDER_SNOW_BUCKET, CraftItemStack.asBukkitCopy(result).getType());
+            assertFalse(CraftItemStack.asBukkitCopy(result).hasItemMeta());
+            assertEquals(1, result.getCount());
+            // Search presentation is supplied by the ordinary native translated output, not a custom name.
+            assertEquals("item.minecraft.powder_snow_bucket", assertInstanceOf(
+                    net.minecraft.network.chat.contents.TranslatableContents.class, result.getHoverName().getContents()).getKey());
+            var displays = new java.util.ArrayList<net.minecraft.world.item.crafting.display.RecipeDisplayEntry>();
+            f.manager.listDisplaysForRecipe(f.powder().id(), displays::add);
+            var id = displays.getFirst().id();
+            var powderPackets = f.packets.packets.stream().filter(ClientboundRecipeBookAddPacket.class::isInstance)
+                    .map(ClientboundRecipeBookAddPacket.class::cast)
+                    .filter(packet -> packet.entries().stream().anyMatch(NativePowderSnowBookTest::powderEntry)).toList();
+            assertEquals(1, powderPackets.size());
+            var packet = powderPackets.getFirst();
+            var entry = packet.entries().stream().filter(NativePowderSnowBookTest::powderEntry).findFirst().orElseThrow();
+            assertEquals(id, entry.contents().id());
+            assertEquals(1, packet.entries().stream().filter(NativePowderSnowBookTest::powderEntry).count());
+            assertEquals(RecipeBookCategories.CRAFTING_MISC, entry.contents().category());
+            assertTrue(entry.notification());
+            assertTrue(entry.highlight());
+            assertEquals(2, entry.contents().craftingRequirements().orElseThrow().size());
+            var buffer = new net.minecraft.network.RegistryFriendlyByteBuf(io.netty.buffer.Unpooled.buffer(),
+                    org.bukkit.craftbukkit.CraftRegistry.getMinecraftRegistry());
+            try {
+                ClientboundRecipeBookAddPacket.STREAM_CODEC.encode(buffer, packet);
+                var decoded = ClientboundRecipeBookAddPacket.STREAM_CODEC.decode(buffer);
+                assertEquals(packet, decoded);
+                assertFalse(buffer.isReadable());
+            } finally {
+                buffer.release();
+            }
+            var powderEvents = f.discoveries.stream().filter(e -> e.getRecipe().equals(KEY)).toList();
+            assertEquals(1, powderEvents.size());
+            assertTrue(powderEvents.getFirst().shouldShowNotification());
+            f.actor.events.callEvent(new PlayerJoinEvent(f.actor.player, "repeat"));
+            assertEquals(1, f.discoveries.stream().filter(e -> e.getRecipe().equals(KEY)).count());
+            assertEquals(0, NativePowderSnowFixture.count(f.actor.realInventory, Material.POWDER_SNOW_BUCKET));
+            assertTrue(f.menu.craftSlots.isEmpty());
+        }
+    }
+
+    @Test
+    void nativeKnownHighlightCodecJoinReconnectDisableAndActualReenableRetainUnrelatedState() throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, 3)) {
+            var vanillaKey = NativePowderSnowFixture.nativeKey(VANILLA);
+            f.book.add(vanillaKey);
+            f.book.setBookSetting(net.minecraft.world.inventory.RecipeBookType.CRAFTING, true, true);
+            var joined = f.joiningPlayer(null);
+            joined.book().add(vanillaKey);
+            f.actor.events.callEvent(new PlayerJoinEvent(joined.player(), "join"));
+            assertTrue(joined.book().contains(NativePowderSnowFixture.nativeKey(KEY)));
+            assertTrue(joined.book().contains(vanillaKey));
+            assertEquals(5, addedEntries(joined.sent()));
+            f.actor.events.callEvent(new PlayerJoinEvent(joined.player(), "idempotent"));
+            assertEquals(5, addedEntries(joined.sent()));
+            var packed = f.book.pack();
+            assertTrue(packed.highlight().contains(NativePowderSnowFixture.nativeKey(KEY)));
+            var nbt = ServerRecipeBook.Packed.CODEC.encodeStart(net.minecraft.nbt.NbtOps.INSTANCE, packed).getOrThrow();
+            var decoded = ServerRecipeBook.Packed.CODEC.parse(net.minecraft.nbt.NbtOps.INSTANCE, nbt).getOrThrow();
+            var reconnected = f.joiningPlayer(decoded);
+            assertPackedEquals(packed, reconnected.book().pack());
+            assertTrue(reconnected.book().isOpen(net.minecraft.world.inventory.RecipeBookType.CRAFTING));
+            assertTrue(reconnected.book().isFiltering(net.minecraft.world.inventory.RecipeBookType.CRAFTING));
+            f.actor.events.callEvent(new PlayerJoinEvent(reconnected.player(), "reconnected"));
+            assertTrue(reconnected.sent().isEmpty(), "No second discovery/notification for known recipe");
+            f.actor.plugin.setEnabled(false);
+            assertTrue(f.registered.isEmpty());
+            assertPackedEquals(packed, f.book.pack());
+            assertPackedEquals(packed, reconnected.book().pack());
+            var disabledJoiner = f.joiningPlayer(null);
+            f.actor.events.callEvent(new PlayerJoinEvent(disabledJoiner.player(), "disabled"));
+            assertTrue(disabledJoiner.book().pack().known().isEmpty());
+            doReturn(List.of(f.actor.player, reconnected.player())).when(f.actor.server).getOnlinePlayers();
+            f.actor.plugin.setEnabled(true);
+            assertEquals(5, f.registered.size());
+            assertTrue(reconnected.sent().isEmpty());
+            assertPackedEquals(packed, f.book.pack());
+            assertEquals(1, f.discoveries.stream().filter(e -> e.getRecipe().equals(KEY) && e.getPlayer() == f.actor.player).count());
+            f.actor.events.callEvent(new PlayerJoinEvent(disabledJoiner.player(), "enabled"));
+            assertTrue(disabledJoiner.book().contains(NativePowderSnowFixture.nativeKey(KEY)));
+            f.actor.realInventory.setItem(0, CraftItemStack.asNMSCopy(new org.bukkit.inventory.ItemStack(Material.SNOW_BLOCK)));
+            f.actor.realInventory.setItem(1, CraftItemStack.asNMSCopy(new org.bukkit.inventory.ItemStack(Material.BUCKET)));
+            f.autofill(false);
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.PICKUP);
+            assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast());
+            assertEquals(Material.POWDER_SNOW_BUCKET, CraftItemStack.asBukkitCopy(f.menu.getCarried()).getType());
+            f.actor.assertNoEventErrors();
+        }
+    }
+
+    @Test
+    void nativeDiscoveryCancellationAndPerPlayerPortFailureAreIsolatedAndRetryOnRealJoin() throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, 2)) {
+            var cancelled = f.joiningPlayer(null);
+            var failed = f.joiningPlayer(null);
+            var healthy = f.joiningPlayer(null);
+            var cancel = new AtomicBoolean(true);
+            f.actor.events.registerEvent(PlayerRecipeDiscoverEvent.class, new Listener() {}, EventPriority.HIGHEST,
+                    (ignored, raw) -> {
+                        var event = (PlayerRecipeDiscoverEvent) raw;
+                        if (event.getPlayer() == cancelled.player() && event.getRecipe().equals(KEY)) event.setCancelled(cancel.get());
+                    }, f.actor.plugin, false);
+            var injected = new IllegalStateException("injected player transport failure");
+            doThrow(injected).when(failed.player()).discoverRecipes(List.of(KEY));
+            for (var player : List.of(cancelled, failed, healthy)) f.actor.events.callEvent(new PlayerJoinEvent(player.player(), "join"));
+            var key = NativePowderSnowFixture.nativeKey(KEY);
+            assertFalse(cancelled.book().contains(key));
+            assertFalse(failed.book().contains(key));
+            assertTrue(healthy.book().contains(key));
+            assertEquals(4, cancelled.book().pack().known().size());
+            assertEquals(4, failed.book().pack().known().size());
+            assertEquals(5, healthy.book().pack().known().size());
+            assertEquals(4, addedEntries(cancelled.sent()));
+            cancel.set(false);
+            doCallRealMethod().when(failed.player()).discoverRecipes(any());
+            f.actor.events.callEvent(new PlayerJoinEvent(cancelled.player(), "retry"));
+            f.actor.events.callEvent(new PlayerJoinEvent(failed.player(), "retry"));
+            assertTrue(cancelled.book().contains(key));
+            assertTrue(failed.book().contains(key));
+            assertEquals(5, addedEntries(cancelled.sent()));
+            f.actor.events.callEvent(new PlayerJoinEvent(cancelled.player(), "known"));
+            assertEquals(5, addedEntries(cancelled.sent()));
+            assertEquals(0, NativePowderSnowFixture.count(f.actor.realInventory, Material.POWDER_SNOW_BUCKET));
+            assertEquals(List.of(injected), f.actor.eventErrors, "Only the deliberately injected discovery failure is logged");
+        }
+    }
+}

src/nativeTest/java/games/dmg/spigotinventoryhelper/NativePowderSnowFixture.java

@@ -0,0 +1,191 @@
+package games.dmg.spigotinventoryhelper;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.stats.ServerRecipeBook;
+import net.minecraft.world.flag.FeatureFlags;
+import net.minecraft.world.inventory.AbstractCraftingMenu;
+import net.minecraft.world.inventory.ContainerLevelAccess;
+import net.minecraft.world.inventory.CraftingMenu;
+import net.minecraft.world.item.crafting.CraftingRecipe;
+import net.minecraft.world.item.crafting.RecipeHolder;
+import net.minecraft.world.item.crafting.RecipeManager;
+import net.minecraft.world.item.crafting.RecipeMap;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.bukkit.craftbukkit.CraftRegistry;
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.craftbukkit.inventory.CraftRecipe;
+import org.bukkit.craftbukkit.util.CraftNamespacedKey;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerRecipeDiscoverEvent;
+import org.bukkit.inventory.Recipe;
+import org.bukkit.inventory.ShapedRecipe;
+import org.bukkit.inventory.ShapelessRecipe;
+
+/** Reuses strict actor/packet ports. Native recipe manager/book/menu/result/event code stays real.
+ * The Server.addRecipe port converts the exact recipe submitted by actual onEnable, following
+ * pinned CraftShaped/ShapelessRecipe conversion (including MaterialChoice's native matching).
+ * No worlds or clients run; packets are captured by the existing native synchronizer port.
+ */
+final class NativePowderSnowFixture implements AutoCloseable {
+    final NativeAnvilFixture actor;
+    final NativeAnvilPacketFixture packets;
+    final RecipeManager manager;
+    final ServerRecipeBook book;
+    final Map<NamespacedKey, Recipe> registered = new HashMap<>();
+    final Map<NamespacedKey, RecipeHolder<CraftingRecipe>> holders = new HashMap<>();
+    final List<PlayerRecipeDiscoverEvent> discoveries = new ArrayList<>();
+    final AbstractCraftingMenu menu;
+
+    NativePowderSnowFixture(Path directory, int width) throws Exception {
+        actor = new NativeAnvilFixture(directory);
+        packets = new NativeAnvilPacketFixture(actor);
+        actor.events.registerEvent(PlayerRecipeDiscoverEvent.class, new Listener() {}, EventPriority.MONITOR,
+                (ignored, event) -> discoveries.add((PlayerRecipeDiscoverEvent) event), actor.plugin, false);
+        actor.plugin.setEnabled(false);
+        manager = new RecipeManager(CraftRegistry.getMinecraftRegistry());
+        when(packets.nativeServer.getRecipeManager()).thenReturn(manager);
+        when(actor.level.recipeAccess()).thenReturn(manager);
+        when(actor.level.getGameRules()).thenReturn(
+                new net.minecraft.world.level.gamerules.GameRules(FeatureFlags.VANILLA_SET));
+        book = new ServerRecipeBook(manager::listDisplaysForRecipe);
+        var bookField = net.minecraft.server.level.ServerPlayer.class.getDeclaredField("recipeBook");
+        assertEquals(ServerRecipeBook.class, bookField.getType());
+        bookField.setAccessible(true);
+        bookField.set(actor.nativePlayer, book);
+        when(actor.nativePlayer.getRecipeBook()).thenReturn(book);
+        when(actor.nativePlayer.getAdvancements()).thenReturn(mock(net.minecraft.server.PlayerAdvancements.class));
+        doCallRealMethod().when(actor.nativePlayer).awardRecipes(any());
+        doCallRealMethod().when(actor.player).hasDiscoveredRecipe(any());
+        doCallRealMethod().when(actor.player).discoverRecipes(any());
+        when(actor.server.getRecipe(any(NamespacedKey.class))).thenAnswer(inv -> registered.get(inv.getArgument(0)));
+        when(actor.server.addRecipe(any(Recipe.class))).thenAnswer(inv -> {
+            Recipe bukkit = inv.getArgument(0);
+            NamespacedKey key = ((Keyed) bukkit).getKey();
+            if (registered.putIfAbsent(key, bukkit) != null) return false;
+            holders.put(key, new RecipeHolder<>(nativeKey(key), convert(bukkit)));
+            refreshManager();
+            return true;
+        });
+        when(actor.server.removeRecipe(any(NamespacedKey.class))).thenAnswer(inv -> {
+            NamespacedKey key = inv.getArgument(0);
+            holders.remove(key);
+            refreshManager();
+            return registered.remove(key) != null;
+        });
+        doReturn(List.of(actor.player)).when(actor.server).getOnlinePlayers();
+        actor.plugin.setEnabled(true);
+        assertTrue(book.contains(nativeKey(NativePowderSnowRecipeTest.KEY)));
+        assertEquals(5, registered.size());
+        assertEquals(5, discoveries.size());
+        assertEquals(0, count(actor.realInventory, org.bukkit.Material.POWDER_SNOW_BUCKET));
+        if (width == 2) {
+            menu = packets.inventoryMenu;
+        } else if (width == 3) {
+            when(actor.level.getBlockState(actor.position)).thenReturn(
+                    net.minecraft.world.level.block.Blocks.CRAFTING_TABLE.defaultBlockState());
+            menu = new CraftingMenu(8, actor.realInventory, ContainerLevelAccess.create(actor.level, actor.position));
+            menu.setTitle(net.minecraft.network.chat.Component.literal("Crafting"));
+        } else {
+            throw new IllegalArgumentException("Unsupported grid width " + width);
+        }
+        actor.nativePlayer.containerMenu = menu;
+        menu.setSynchronizer(packets.synchronizer);
+        actor.assertNoEventErrors();
+    }
+
+    /** A later connection has a real native book, with only player/world/network ports doubled. */
+    BookPlayer joiningPlayer(ServerRecipeBook.Packed saved) throws Exception {
+        var nativePlayer = mock(net.minecraft.server.level.ServerPlayer.class);
+        var player = mock(org.bukkit.craftbukkit.entity.CraftPlayer.class);
+        var recipeBook = new ServerRecipeBook(manager::listDisplaysForRecipe);
+        if (saved != null) recipeBook.loadUntrusted(saved, key -> true);
+        var field = net.minecraft.server.level.ServerPlayer.class.getDeclaredField("recipeBook");
+        assertEquals(ServerRecipeBook.class, field.getType());
+        field.setAccessible(true);
+        field.set(nativePlayer, recipeBook);
+        when(nativePlayer.getRecipeBook()).thenReturn(recipeBook);
+        when(nativePlayer.getBukkitEntity()).thenReturn(player);
+        when(nativePlayer.level()).thenReturn(actor.level);
+        when(nativePlayer.getAdvancements()).thenReturn(mock(net.minecraft.server.PlayerAdvancements.class));
+        when(player.getHandle()).thenReturn(nativePlayer);
+        when(player.getName()).thenReturn("JoiningPowderPlayer");
+        doCallRealMethod().when(nativePlayer).awardRecipes(any());
+        doCallRealMethod().when(player).hasDiscoveredRecipe(any());
+        doCallRealMethod().when(player).discoverRecipes(any());
+        nativePlayer.connection = mock(net.minecraft.server.network.ServerGamePacketListenerImpl.class);
+        var sent = new ArrayList<net.minecraft.network.protocol.Packet<?>>();
+        doAnswer(inv -> { sent.add(inv.getArgument(0)); return null; })
+                .when(nativePlayer.connection).send(any(net.minecraft.network.protocol.Packet.class));
+        return new BookPlayer(player, nativePlayer, recipeBook, sent);
+    }
+
+    record BookPlayer(org.bukkit.craftbukkit.entity.CraftPlayer player,
+            net.minecraft.server.level.ServerPlayer nativePlayer, ServerRecipeBook book,
+            List<net.minecraft.network.protocol.Packet<?>> sent) {}
+
+    RecipeHolder<CraftingRecipe> powder() { return holders.get(NativePowderSnowRecipeTest.KEY); }
+
+    net.minecraft.world.inventory.RecipeBookMenu.PostPlaceAction autofill(boolean batch) {
+        var action = menu.handlePlacement(batch, false, powder(), actor.level, actor.realInventory);
+        actor.assertNoEventErrors();
+        return action;
+    }
+
+    List<org.bukkit.inventory.ItemStack> gridSnapshot() {
+        return menu.craftSlots.getItems().stream().map(CraftItemStack::asBukkitCopy).toList();
+    }
+
+    static long count(net.minecraft.world.Container container, org.bukkit.Material material) {
+        return java.util.stream.IntStream.range(0, container.getContainerSize()).mapToObj(container::getItem)
+                .map(CraftItemStack::asBukkitCopy).filter(item -> item.getType() == material)
+                .mapToInt(org.bukkit.inventory.ItemStack::getAmount).sum();
+    }
+
+    static ResourceKey<net.minecraft.world.item.crafting.Recipe<?>> nativeKey(NamespacedKey key) {
+        return CraftNamespacedKey.toResourceKey(Registries.RECIPE, key);
+    }
+
+    private void refreshManager() {
+        manager.recipes = RecipeMap.create(new ArrayList<RecipeHolder<?>>(holders.values()));
+        manager.finalizeRecipeLoading(FeatureFlags.VANILLA_SET);
+    }
+
+    private static CraftingRecipe convert(Recipe recipe) {
+        if (recipe instanceof ShapelessRecipe shapeless) {
+            return new net.minecraft.world.item.crafting.ShapelessRecipe(
+                    new net.minecraft.world.item.crafting.Recipe.CommonInfo(true),
+                    new CraftingRecipe.CraftingBookInfo(CraftRecipe.getCategory(shapeless.getCategory()), shapeless.getGroup()),
+                    CraftItemStack.asTemplate(shapeless.getResult()), shapeless.getChoiceList().stream()
+                            .map(choice -> CraftRecipe.toIngredient(choice, true)).toList());
+        }
+        if (recipe instanceof ShapedRecipe shaped) {
+            Map<Character, net.minecraft.world.item.crafting.Ingredient> ingredients = new HashMap<>();
+            shaped.getChoiceMap().forEach((symbol, choice) -> {
+                if (choice != null) ingredients.put(symbol, CraftRecipe.toIngredient(choice, true));
+            });
+            return new net.minecraft.world.item.crafting.ShapedRecipe(
+                    new net.minecraft.world.item.crafting.Recipe.CommonInfo(true),
+                    new CraftingRecipe.CraftingBookInfo(CraftRecipe.getCategory(shaped.getCategory()), shaped.getGroup()),
+                    net.minecraft.world.item.crafting.ShapedRecipePattern.of(ingredients, shaped.getShape()),
+                    CraftItemStack.asTemplate(shaped.getResult()));
+        }
+        throw new AssertionError("Unexpected registered recipe " + recipe.getClass());
+    }
+
+    @Override public void close() {
+        packets.close();
+        actor.close();
+    }
+}

src/nativeTest/java/games/dmg/spigotinventoryhelper/NativePowderSnowPluginWiringTest.java

@@ -0,0 +1,513 @@
+package games.dmg.spigotinventoryhelper;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.reset;
+import static org.mockito.Mockito.when;
+
+import io.papermc.paper.plugin.manager.PaperPluginManagerImpl;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.logging.Handler;
+import java.util.logging.Level;
+import java.util.logging.LogRecord;
+import java.util.logging.Logger;
+import org.bukkit.Bukkit;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Server;
+import org.bukkit.command.SimpleCommandMap;
+import org.bukkit.craftbukkit.inventory.CraftItemFactory;
+import org.bukkit.craftbukkit.util.CraftMagicNumbers;
+import org.bukkit.entity.Player;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.inventory.Recipe;
+import org.bukkit.plugin.InvalidDescriptionException;
+import org.bukkit.plugin.PluginDescriptionFile;
+import org.bukkit.plugin.PluginManager;
+import org.bukkit.plugin.java.JavaPluginLoader;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/** Real enable/disable callbacks using Bukkit's explicit initialization and existing native fixtures. */
+class NativePowderSnowPluginWiringTest {
+    private static final NamespacedKey POWDER = key("snow_powder_snow");
+    private static final Set<NamespacedKey> EXISTING = Set.of(key("string_cobweb"), key("dropper_dispenser"),
+            key("sorting_stick_recipe_chest"), key("sorting_stick_recipe_barrel"));
+    private static final NamespacedKey VANILLA = new NamespacedKey("minecraft", "stick");
+    private static Server previousServer;
+    private static Server serverUnderTest;
+    @TempDir Path directory;
+    private Map<NamespacedKey, Recipe> registry;
+    private PaperPluginManagerImpl events;
+    private SimpleCommandMap commands;
+    private Logger logger;
+    private List<LogRecord> logs;
+    private Handler logHandler;
+    private SpigotInventoryHelperPlugin createdPlugin;
+    private com.comphenix.protocol.ProtocolManager protocol;
+    private List<com.comphenix.protocol.events.PacketListener> protocolListeners;
+
+    @BeforeAll
+    static void bootstrap() throws Exception {
+        NativeRuntime.bootstrap();
+        previousServer = Bukkit.getServer();
+        // ProtocolLib derives CraftBukkit's package from this external server's concrete class.
+        serverUnderTest = mock(org.bukkit.craftbukkit.CraftServer.class,
+                org.mockito.Mockito.withSettings().mockMaker(org.mockito.MockMakers.INLINE));
+        setServer(serverUnderTest);
+    }
+
+    @BeforeEach
+    void configureServer() {
+        reset(serverUnderTest);
+        protocol = mock(com.comphenix.protocol.ProtocolManager.class);
+        protocolListeners = new ArrayList<>();
+        doAnswer(inv -> { protocolListeners.add(inv.getArgument(0)); return null; }).when(protocol).addPacketListener(any());
+        doAnswer(inv -> { protocolListeners.remove(inv.getArgument(0)); return null; }).when(protocol).removePacketListener(any());
+        when(serverUnderTest.getItemFactory()).thenAnswer(invocation -> CraftItemFactory.instance());
+        when(serverUnderTest.getUnsafe()).thenReturn(CraftMagicNumbers.INSTANCE);
+        when(serverUnderTest.isPrimaryThread()).thenReturn(true);
+        when(serverUnderTest.getVersion()).thenReturn("Purpur 2618 (MC: 26.2)");
+        when(serverUnderTest.getMinecraftVersion()).thenReturn("26.2");
+        when(serverUnderTest.getBukkitVersion()).thenReturn("26.2.build.2618-stable");
+        when(serverUnderTest.getWarningState()).thenReturn(org.bukkit.Warning.WarningState.DEFAULT);
+        logger = Logger.getAnonymousLogger();
+        logs = new ArrayList<>();
+        logHandler = new Handler() {
+            @Override public void publish(LogRecord record) { logs.add(record); }
+            @Override public void flush() {}
+            @Override public void close() {}
+        };
+        logger.addHandler(logHandler);
+        when(serverUnderTest.getLogger()).thenReturn(logger);
+        registry = new HashMap<>();
+        registry.put(VANILLA, mock(Recipe.class));
+        when(serverUnderTest.getRecipe(any(NamespacedKey.class))).thenAnswer(
+                invocation -> registry.get(invocation.getArgument(0)));
+        when(serverUnderTest.addRecipe(any(Recipe.class))).thenAnswer(invocation -> {
+            Recipe recipe = invocation.getArgument(0);
+            return registry.putIfAbsent(((Keyed) recipe).getKey(), recipe) == null;
+        });
+        when(serverUnderTest.removeRecipe(any(NamespacedKey.class))).thenAnswer(
+                invocation -> registry.remove(invocation.getArgument(0)) != null);
+        commands = new SimpleCommandMap(serverUnderTest, new HashMap<>());
+        when(serverUnderTest.getPluginCommand(any(String.class))).thenAnswer(invocation ->
+                commands.getCommand(invocation.getArgument(0)));
+        var scheduler = mock(org.bukkit.craftbukkit.scheduler.CraftScheduler.class);
+        when(serverUnderTest.getScheduler()).thenReturn(scheduler);
+        when(scheduler.runTaskTimer(any(), any(Runnable.class),
+                org.mockito.ArgumentMatchers.anyLong(), org.mockito.ArgumentMatchers.anyLong()))
+                .thenAnswer(ignored -> mock(org.bukkit.scheduler.BukkitTask.class));
+        events = new PaperPluginManagerImpl(serverUnderTest, commands, null);
+        when(serverUnderTest.getPluginManager()).thenReturn(events);
+        doReturn(List.of()).when(serverUnderTest).getOnlinePlayers();
+    }
+
+    @AfterEach
+    void removeLogHandler() {
+        logger.removeHandler(logHandler);
+        if (createdPlugin != null) {
+            createdPlugin.getLogger().removeHandler(logHandler);
+        }
+    }
+
+    @AfterAll
+    static void restoreServer() throws Exception {
+        setServer(previousServer);
+    }
+
+    @Test
+    void actualEnableDiscoversOnlineAndJoinersIdempotentlyAndReenablesWithoutLosingKnowledge() {
+        Set<NamespacedKey> onlineKnown = new LinkedHashSet<>(Set.of(VANILLA));
+        Set<NamespacedKey> joiningKnown = new LinkedHashSet<>(Set.of(VANILLA));
+        AtomicInteger onlineGrants = new AtomicInteger();
+        AtomicInteger joiningGrants = new AtomicInteger();
+        Player online = player("Online", onlineKnown, onlineGrants, new AtomicBoolean());
+        Player joining = player("Joining", joiningKnown, joiningGrants, new AtomicBoolean());
+        doReturn(List.of(online)).when(serverUnderTest).getOnlinePlayers();
+        Recipe vanilla = registry.get(VANILLA);
+        var plugin = plugin();
+        try {
+            plugin.setEnabled(true);
+            assertTrue(registry.keySet().containsAll(EXISTING));
+            assertTrue(registry.containsKey(POWDER));
+            assertEquals(expectedKnown(), onlineKnown);
+            plugin.setEnabled(true);
+            events.callEvent(new PlayerJoinEvent(joining, "joined"));
+            events.callEvent(new PlayerJoinEvent(joining, "joined again"));
+            assertEquals(expectedKnown(), joiningKnown);
+            assertEquals(1, onlineGrants.get());
+            assertEquals(1, joiningGrants.get());
+
+            plugin.setEnabled(false);
+            assertEquals(Set.of(VANILLA), registry.keySet());
+            assertSame(vanilla, registry.get(VANILLA));
+            assertEquals(expectedKnown(), onlineKnown);
+            assertEquals(expectedKnown(), joiningKnown);
+            Set<NamespacedKey> afterDisable = new LinkedHashSet<>();
+            events.callEvent(new PlayerJoinEvent(player("AfterDisable", afterDisable,
+                    new AtomicInteger(), new AtomicBoolean()), "joined"));
+            assertTrue(afterDisable.isEmpty(), "Disabled listeners must not award recipes");
+
+            plugin.setEnabled(true);
+            assertTrue(registry.keySet().containsAll(EXISTING));
+            assertTrue(registry.containsKey(POWDER));
+            assertEquals(1, onlineGrants.get(), "Re-enable must not rediscover a known recipe");
+            assertNoSevereLogs();
+        } finally {
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @Test
+    void powderSnowKeyConflictPreservesForeignRecipeAndExistingFeaturesWithoutDiscovery() {
+        Recipe conflict = mock(Recipe.class);
+        registry.put(POWDER, conflict);
+        Set<NamespacedKey> known = new LinkedHashSet<>(Set.of(VANILLA));
+        AtomicInteger grants = new AtomicInteger();
+        doReturn(List.of(player("Online", known, grants, new AtomicBoolean())))
+                .when(serverUnderTest).getOnlinePlayers();
+        var plugin = plugin();
+        try {
+            plugin.setEnabled(true);
+            assertSame(conflict, registry.get(POWDER));
+            assertTrue(registry.keySet().containsAll(EXISTING));
+            assertTrue(known.containsAll(EXISTING));
+            assertFalse(known.contains(POWDER));
+            assertEquals(0, grants.get());
+            plugin.setEnabled(false);
+            assertEquals(Set.of(VANILLA, POWDER), registry.keySet());
+            assertSame(conflict, registry.get(POWDER));
+
+            registry.remove(POWDER);
+            plugin.setEnabled(true);
+            assertTrue(registry.containsKey(POWDER));
+            assertTrue(known.contains(POWDER));
+            assertEquals(1, grants.get());
+            assertEquals(1, logs.stream().filter(r -> r.getLevel() == Level.SEVERE).count(),
+                    "Only the deliberately injected key conflict is severe");
+        } finally {
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @Test
+    void onePlayersDiscoveryFailureDoesNotBlockOthersAndCanRetryOnJoin() {
+        Set<NamespacedKey> failedKnown = new LinkedHashSet<>(Set.of(VANILLA));
+        Set<NamespacedKey> healthyKnown = new LinkedHashSet<>(Set.of(VANILLA));
+        AtomicBoolean fail = new AtomicBoolean(true);
+        AtomicInteger failedGrants = new AtomicInteger();
+        Player failed = player("Failed", failedKnown, failedGrants, fail);
+        Player healthy = player("Healthy", healthyKnown, new AtomicInteger(), new AtomicBoolean());
+        doReturn(List.of(failed, healthy)).when(serverUnderTest).getOnlinePlayers();
+        var plugin = plugin();
+        try {
+            plugin.setEnabled(true);
+            assertFalse(failedKnown.contains(POWDER));
+            assertEquals(expectedKnown(), healthyKnown);
+            assertTrue(failedKnown.containsAll(EXISTING));
+            fail.set(false);
+            events.callEvent(new PlayerJoinEvent(failed, "retry"));
+            assertEquals(expectedKnown(), failedKnown);
+            assertEquals(1, failedGrants.get());
+            assertNoSevereLogs();
+            assertEquals(1, logs.stream().filter(r -> r.getLevel() == Level.WARNING).count());
+        } finally {
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @Test
+    void partialDiscoveryListenerFailureRollsBackOnlyPowderSnowAndWithholdsJoinDiscovery() {
+        PluginManager throwing = mock(PluginManager.class);
+        AtomicInteger discoveries = new AtomicInteger();
+        doAnswer(invocation -> {
+            Listener listener = invocation.getArgument(0);
+            org.bukkit.plugin.Plugin owner = invocation.getArgument(1);
+            events.registerEvents(listener, owner);
+            if (listener instanceof RecipeDiscovery && discoveries.incrementAndGet() == 4) {
+                throw new IllegalStateException("simulated post-listener-registration failure");
+            }
+            return null;
+        }).when(throwing).registerEvents(any(), any());
+        when(serverUnderTest.getPluginManager()).thenReturn(throwing);
+        var plugin = plugin();
+        try {
+            plugin.setEnabled(true);
+            assertFalse(registry.containsKey(POWDER));
+            assertTrue(registry.keySet().containsAll(EXISTING));
+            Set<NamespacedKey> known = new LinkedHashSet<>(Set.of(VANILLA));
+            events.callEvent(new PlayerJoinEvent(player("Joining", known, new AtomicInteger(),
+                    new AtomicBoolean()), "joined"));
+            assertTrue(known.containsAll(EXISTING));
+            assertFalse(known.contains(POWDER));
+            assertEquals(1, logs.stream().filter(r -> r.getLevel() == Level.SEVERE).count(),
+                    "Only the deliberately injected listener failure is severe");
+        } finally {
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(strings = {"refused", "before-insert", "after-insert", "lookup"})
+    void registrationPortFailuresPreserveOtherFeaturesAndRetryThroughActualEnable(String failure) {
+        var fail = new AtomicBoolean(true);
+        when(serverUnderTest.getRecipe(any(NamespacedKey.class))).thenAnswer(invocation -> {
+            NamespacedKey requested = invocation.getArgument(0);
+            if (requested.equals(POWDER) && failure.equals("lookup") && fail.get())
+                throw new IllegalStateException("injected lookup failure");
+            return registry.get(requested);
+        });
+        when(serverUnderTest.addRecipe(any(Recipe.class))).thenAnswer(invocation -> {
+            Recipe recipe = invocation.getArgument(0);
+            var key = ((Keyed) recipe).getKey();
+            if (key.equals(POWDER) && fail.get()) {
+                if (failure.equals("refused")) return false;
+                if (failure.equals("before-insert")) throw new IllegalStateException("injected pre-insert failure");
+                if (failure.equals("after-insert")) {
+                    registry.put(key, recipe);
+                    throw new IllegalStateException("injected post-insert failure");
+                }
+            }
+            return registry.putIfAbsent(key, recipe) == null;
+        });
+        var known = new LinkedHashSet<>(Set.of(VANILLA));
+        Player online = player("Online", known, new AtomicInteger(), new AtomicBoolean());
+        doReturn(List.of(online)).when(serverUnderTest).getOnlinePlayers();
+        Recipe vanilla = registry.get(VANILLA);
+        var plugin = plugin();
+        try {
+            plugin.setEnabled(true);
+            assertFalse(registry.containsKey(POWDER));
+            assertFalse(known.contains(POWDER));
+            assertTrue(registry.keySet().containsAll(EXISTING));
+            assertTrue(known.containsAll(EXISTING));
+            assertSame(vanilla, registry.get(VANILLA));
+            // Sorting/admin/native-anvil registration is not withheld by a failed independent recipe.
+            assertNotNull(plugin.sortingSticks());
+            assertFalse(protocolListeners.isEmpty());
+            plugin.setEnabled(false);
+            assertEquals(Set.of(VANILLA), registry.keySet());
+            assertSame(vanilla, registry.get(VANILLA));
+            fail.set(false);
+            plugin.setEnabled(true);
+            assertTrue(registry.containsKey(POWDER));
+            assertTrue(known.contains(POWDER));
+            assertEquals(1, logs.stream().filter(r -> r.getLevel() == Level.SEVERE).count());
+        } finally {
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(strings = {"false", "throw"})
+    void realLifecycleRemovalFailureRetainsOwnershipForRetryWithoutListenersOrOtherRecipeLoss(String failure) {
+        var plugin = plugin();
+        plugin.setEnabled(true);
+        var separateKey = key("powder_removal_probe");
+        var lifecycle = new RecipeLifecycle(serverUnderTest, plugin,
+                new PowderSnowRecipeRegistrar(separateKey), plugin.getLogger());
+        var fail = new AtomicBoolean(true);
+        try {
+            assertTrue(lifecycle.enable());
+            Set<NamespacedKey> before = new LinkedHashSet<>(registry.keySet());
+            when(serverUnderTest.removeRecipe(any(NamespacedKey.class))).thenAnswer(invocation -> {
+                NamespacedKey requested = invocation.getArgument(0);
+                if (requested.equals(separateKey) && fail.get()) {
+                    if (failure.equals("false")) return false;
+                    throw new IllegalStateException("injected removal failure");
+                }
+                return registry.remove(requested) != null;
+            });
+            assertThrows(IllegalStateException.class, lifecycle::disable);
+            assertEquals(before, registry.keySet());
+            var known = new LinkedHashSet<NamespacedKey>();
+            events.callEvent(new PlayerJoinEvent(player("After failed disable", known,
+                    new AtomicInteger(), new AtomicBoolean()), "joined"));
+            assertFalse(known.contains(separateKey), "Unregistered discovery must not grant the stranded recipe");
+            assertTrue(known.contains(POWDER), "Other independently active listeners remain usable");
+            fail.set(false);
+            lifecycle.disable();
+            before.remove(separateKey);
+            assertEquals(before, registry.keySet());
+            assertTrue(lifecycle.enable());
+            assertTrue(registry.containsKey(separateKey));
+            lifecycle.disable();
+            assertEquals(before, registry.keySet());
+        } finally {
+            fail.set(false);
+            lifecycle.disable();
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @Test
+    void exceptionAfterSuccessfulRemovalCanRetryCleanupAndRegisterAgain() {
+        var plugin = plugin();
+        plugin.setEnabled(true);
+        var key = key("powder_post_removal_probe");
+        var lifecycle = new RecipeLifecycle(serverUnderTest, plugin,
+                new PowderSnowRecipeRegistrar(key), plugin.getLogger());
+        try {
+            assertTrue(lifecycle.enable());
+            Set<NamespacedKey> before = new LinkedHashSet<>(registry.keySet());
+            when(serverUnderTest.removeRecipe(any(NamespacedKey.class))).thenAnswer(invocation -> {
+                NamespacedKey requested = invocation.getArgument(0);
+                boolean removed = registry.remove(requested) != null;
+                if (requested.equals(key) && removed)
+                    throw new IllegalStateException("injected exception after successful removal");
+                return removed;
+            });
+            assertThrows(IllegalStateException.class, lifecycle::disable);
+            before.remove(key);
+            assertEquals(before, registry.keySet());
+            assertDoesNotThrow(lifecycle::disable, "Absent owned registration must permit cleanup retry");
+            assertTrue(lifecycle.enable());
+            assertTrue(registry.containsKey(key));
+        } finally {
+            when(serverUnderTest.removeRecipe(any(NamespacedKey.class))).thenAnswer(
+                    invocation -> registry.remove(invocation.getArgument(0)) != null);
+            // A deliberately stranded absent registration must not mask the RED assertion in cleanup.
+            if (registry.containsKey(key)) lifecycle.disable();
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    @Test
+    void postInsertionAndRollbackRemovalFailureKeepRealLifecycleRetryable() {
+        var plugin = plugin();
+        plugin.setEnabled(true);
+        var key = key("powder_insertion_probe");
+        var lifecycle = new RecipeLifecycle(serverUnderTest, plugin,
+                new PowderSnowRecipeRegistrar(key), plugin.getLogger());
+        var failRemoval = new AtomicBoolean(true);
+        try {
+            Set<NamespacedKey> before = new LinkedHashSet<>(registry.keySet());
+            when(serverUnderTest.addRecipe(any(Recipe.class))).thenAnswer(invocation -> {
+                Recipe recipe = invocation.getArgument(0);
+                var requested = ((Keyed) recipe).getKey();
+                registry.put(requested, recipe);
+                if (requested.equals(key)) throw new IllegalStateException("injected post-insert failure");
+                return true;
+            });
+            when(serverUnderTest.removeRecipe(any(NamespacedKey.class))).thenAnswer(invocation -> {
+                NamespacedKey requested = invocation.getArgument(0);
+                if (requested.equals(key) && failRemoval.get())
+                    throw new IllegalStateException("injected rollback removal failure");
+                return registry.remove(requested) != null;
+            });
+            assertFalse(lifecycle.enable());
+            assertTrue(registry.containsKey(key), "Failed cleanup honestly retains ownership");
+            assertTrue(registry.keySet().containsAll(before));
+            var known = new LinkedHashSet<NamespacedKey>();
+            events.callEvent(new PlayerJoinEvent(player("During failure", known,
+                    new AtomicInteger(), new AtomicBoolean()), "joined"));
+            assertFalse(known.contains(key));
+            failRemoval.set(false);
+            lifecycle.disable();
+            assertEquals(before, registry.keySet());
+            when(serverUnderTest.addRecipe(any(Recipe.class))).thenAnswer(invocation -> {
+                Recipe recipe = invocation.getArgument(0);
+                return registry.putIfAbsent(((Keyed) recipe).getKey(), recipe) == null;
+            });
+            assertTrue(lifecycle.enable());
+            events.callEvent(new PlayerJoinEvent(player("Retry", known,
+                    new AtomicInteger(), new AtomicBoolean()), "joined"));
+            assertTrue(known.contains(key));
+            assertEquals(1, logs.stream().filter(r -> r.getLevel() == Level.SEVERE).count());
+        } finally {
+            failRemoval.set(false);
+            lifecycle.disable();
+            plugin.setEnabled(false);
+            HandlerList.unregisterAll(plugin);
+        }
+    }
+
+    private SpigotInventoryHelperPlugin plugin() {
+        try {
+            createdPlugin = new SpigotInventoryHelperPlugin(new JavaPluginLoader(serverUnderTest),
+                    NativeAnvilFixture.description(), directory.resolve("data").toFile(),
+                    directory.resolve("plugin.jar").toFile(), () -> 99, () -> 1, protocol,
+                    () -> "Purpur 26.2.build.2618-stable");
+            commands.registerAll(createdPlugin.getName(),
+                    org.bukkit.command.PluginCommandYamlParser.parse(createdPlugin));
+            createdPlugin.getLogger().addHandler(logHandler);
+            return createdPlugin;
+        } catch (java.io.IOException | InvalidDescriptionException exception) {
+            throw new AssertionError("Could not read generated plugin metadata", exception);
+        }
+    }
+
+    private static Player player(String name, Set<NamespacedKey> known,
+            AtomicInteger powderSnowGrants, AtomicBoolean failPowderSnow) {
+        Player player = mock(Player.class);
+        when(player.getName()).thenReturn(name);
+        when(player.hasDiscoveredRecipe(any(NamespacedKey.class))).thenAnswer(
+                invocation -> known.contains(invocation.getArgument(0)));
+        when(player.discoverRecipes(any())).thenAnswer(invocation -> {
+            List<NamespacedKey> requested = ((Collection<?>) invocation.getArgument(0)).stream()
+                    .map(NamespacedKey.class::cast).toList();
+            if (requested.contains(POWDER)) {
+                if (failPowderSnow.get()) {
+                    throw new IllegalStateException("simulated player discovery failure");
+                }
+                powderSnowGrants.incrementAndGet();
+            }
+            known.addAll(requested);
+            return requested.size();
+        });
+        return player;
+    }
+
+    private void assertNoSevereLogs() {
+        assertEquals(0, logs.stream().filter(r -> r.getLevel() == Level.SEVERE).count());
+    }
+
+    private static Set<NamespacedKey> expectedKnown() {
+        Set<NamespacedKey> expected = new LinkedHashSet<>(EXISTING);
+        expected.add(POWDER);
+        expected.add(VANILLA);
+        return expected;
+    }
+
+    private static NamespacedKey key(String name) {
+        return new NamespacedKey("spigotinventoryhelper", name);
+    }
+
+    private static void setServer(Server server) throws Exception {
+        var field = Bukkit.class.getDeclaredField("server");
+        field.setAccessible(true);
+        field.set(null, server);
+    }
+}

src/nativeTest/java/games/dmg/spigotinventoryhelper/NativePowderSnowRecipeTest.java

@@ -0,0 +1,312 @@
+package games.dmg.spigotinventoryhelper;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.nio.file.Path;
+import java.util.List;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.inventory.RecipeChoice;
+import org.bukkit.inventory.ShapelessRecipe;
+import org.bukkit.inventory.recipe.CraftingBookCategory;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/** Actual plugin registration, pinned native crafting engine; no replacement plugin logic. */
+class NativePowderSnowRecipeTest {
+    static final NamespacedKey KEY = new NamespacedKey("spigotinventoryhelper", "snow_powder_snow");
+    @TempDir Path directory;
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void discoveredNativeAutofillAndActualPacketTakePayOnceInBothMenus(int width) throws Exception {
+        try (var fixture = new NativePowderSnowFixture(directory, width)) {
+            var inventory = fixture.actor.realInventory;
+            inventory.setItem(0, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(
+                    new org.bukkit.inventory.ItemStack(Material.SNOW_BLOCK, 2)));
+            inventory.setItem(1, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(
+                    new org.bukkit.inventory.ItemStack(Material.BUCKET, 2)));
+            assertEquals(net.minecraft.world.inventory.RecipeBookMenu.PostPlaceAction.NOTHING, fixture.autofill(false));
+            assertEquals(1, NativePowderSnowFixture.count(fixture.menu.craftSlots, Material.SNOW_BLOCK));
+            assertEquals(1, NativePowderSnowFixture.count(fixture.menu.craftSlots, Material.BUCKET));
+            assertEquals(0, NativePowderSnowFixture.count(inventory, Material.POWDER_SNOW_BUCKET));
+            assertEquals(Material.POWDER_SNOW_BUCKET,
+                    org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(fixture.menu.getResultSlot().getItem()).getType());
+            fixture.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.PICKUP);
+            var event = assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, fixture.packets.clicks.getLast());
+            assertEquals(KEY, ((org.bukkit.Keyed) event.getRecipe()).getKey());
+            assertFalse(event.isCancelled());
+            assertEquals(Material.POWDER_SNOW_BUCKET,
+                    org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(fixture.menu.getCarried()).getType());
+            assertTrue(fixture.menu.craftSlots.isEmpty());
+            assertEquals(1, NativePowderSnowFixture.count(inventory, Material.SNOW_BLOCK));
+            assertEquals(1, NativePowderSnowFixture.count(inventory, Material.BUCKET));
+            fixture.actor.assertNoEventErrors();
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void shapelessNativeMatchingRequiresExactlyBothMaterialsInEveryPairOfPositions(int width) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            var recipe = f.powder().value();
+            for (int snow = 0; snow < width * width; snow++) {
+                for (int bucket = 0; bucket < width * width; bucket++) {
+                    if (snow == bucket) continue;
+                    var items = new java.util.ArrayList<>(java.util.Collections.nCopies(width * width,
+                            net.minecraft.world.item.ItemStack.EMPTY));
+                    items.set(snow, nms(Material.SNOW_BLOCK, 2));
+                    items.set(bucket, nms(Material.BUCKET, 3));
+                    assertTrue(recipe.matches(net.minecraft.world.item.crafting.CraftingInput.of(width, width, items), f.actor.level));
+                    items.set(snow, net.minecraft.world.item.ItemStack.EMPTY);
+                    assertFalse(recipe.matches(net.minecraft.world.item.crafting.CraftingInput.of(width, width, items), f.actor.level));
+                    for (Material wrong : List.of(Material.SNOWBALL, Material.SNOW, Material.DIRT)) {
+                        items.set(snow, nms(wrong, 1));
+                        assertFalse(recipe.matches(net.minecraft.world.item.crafting.CraftingInput.of(width, width, items), f.actor.level));
+                    }
+                    items.set(snow, nms(Material.SNOW_BLOCK, 2));
+                    items.set(bucket, net.minecraft.world.item.ItemStack.EMPTY);
+                    assertFalse(recipe.matches(net.minecraft.world.item.crafting.CraftingInput.of(width, width, items), f.actor.level));
+                    for (Material wrong : List.of(Material.SNOWBALL, Material.SNOW, Material.WATER_BUCKET, Material.POWDER_SNOW_BUCKET)) {
+                        items.set(bucket, nms(wrong, 1));
+                        assertFalse(recipe.matches(net.minecraft.world.item.crafting.CraftingInput.of(width, width, items), f.actor.level));
+                    }
+                    items.set(bucket, nms(Material.BUCKET, 1));
+                    int extra = java.util.stream.IntStream.range(0, items.size())
+                            .filter(i -> items.get(i).isEmpty()).findFirst().orElseThrow();
+                    for (Material material : List.of(Material.BUCKET, Material.SNOW_BLOCK, Material.DIRT)) {
+                        items.set(extra, nms(material, 1));
+                        assertFalse(recipe.matches(net.minecraft.world.item.crafting.CraftingInput.of(width, width, items), f.actor.level));
+                    }
+                }
+            }
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.CsvSource({"2,1", "2,3", "2,16", "3,1", "3,3", "3,16"})
+    void nativeBatchPacketConservesEachBucketAndSnowWithUnstackableOutput(int width, int crafts) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            var inventory = f.actor.realInventory;
+            var keep = marked(Material.DIAMOND, 7);
+            inventory.setItem(20, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(keep));
+            inventory.setItem(0, nms(Material.SNOW_BLOCK, crafts));
+            inventory.setItem(1, nms(Material.BUCKET, crafts));
+            assertEquals(16, nms(Material.BUCKET, 1).getMaxStackSize());
+            assertEquals(1, nms(Material.POWDER_SNOW_BUCKET, 1).getMaxStackSize());
+            assertEquals(net.minecraft.world.inventory.RecipeBookMenu.PostPlaceAction.NOTHING, f.autofill(true));
+            assertEquals(crafts, NativePowderSnowFixture.count(f.menu.craftSlots, Material.BUCKET));
+            assertEquals(crafts, NativePowderSnowFixture.count(f.menu.craftSlots, Material.SNOW_BLOCK));
+            assertEquals(0, NativePowderSnowFixture.count(inventory, Material.POWDER_SNOW_BUCKET));
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.QUICK_MOVE);
+            var event = assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast());
+            assertFalse(event.isCancelled());
+            assertEquals(KEY, ((org.bukkit.Keyed) event.getRecipe()).getKey());
+            assertEquals(crafts, NativePowderSnowFixture.count(inventory, Material.POWDER_SNOW_BUCKET));
+            assertEquals(0, NativePowderSnowFixture.count(inventory, Material.BUCKET));
+            assertEquals(0, NativePowderSnowFixture.count(inventory, Material.SNOW_BLOCK));
+            assertTrue(f.menu.craftSlots.isEmpty());
+            assertTrue(f.menu.getCarried().isEmpty());
+            assertEquals(keep, org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(inventory.getItem(20)));
+            for (var item : inventory.getNonEquipmentItems()) {
+                if (item.is(net.minecraft.world.item.Items.POWDER_SNOW_BUCKET)) ordinaryOutput(item);
+            }
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty),
+                    "Native empty-stack drop calls award nothing");
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void ordinaryPacketPreservesRemainingIngredientMetadataAndAwardsNoExtraBucket(int width) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            var snow = marked(Material.SNOW_BLOCK, 3);
+            var buckets = marked(Material.BUCKET, 3);
+            var keep = marked(Material.DIAMOND, 7);
+            f.actor.realInventory.setItem(20, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(keep));
+            f.menu.craftSlots.setItem(0, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(snow));
+            f.menu.craftSlots.setItem(width * width - 1, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(buckets));
+            var before = f.gridSnapshot();
+            ordinaryOutput(f.menu.getResultSlot().getItem());
+            assertEquals(before, f.gridSnapshot(), "Preview is not payment");
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.PICKUP);
+            assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast());
+            ordinaryOutput(f.menu.getCarried());
+            assertEquals(marked(Material.SNOW_BLOCK, 2), org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(f.menu.craftSlots.getItem(0)));
+            assertEquals(marked(Material.BUCKET, 2), org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(f.menu.craftSlots.getItem(width * width - 1)));
+            assertEquals(0, NativePowderSnowFixture.count(f.actor.realInventory, Material.BUCKET));
+            assertEquals(keep, org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(f.actor.realInventory.getItem(20)));
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty),
+                    "Native empty-stack drop calls award nothing");
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.CsvSource({"2,PICKUP", "2,QUICK_MOVE", "3,PICKUP", "3,QUICK_MOVE"})
+    void actualNativeCraftItemCancellationSpendsNothingAndLaterRetrySucceeds(int width, net.minecraft.world.inventory.ContainerInput input) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            f.actor.realInventory.setItem(0, nms(Material.SNOW_BLOCK, 3));
+            f.actor.realInventory.setItem(1, nms(Material.BUCKET, 3));
+            f.autofill(true);
+            var grid = f.gridSnapshot();
+            var inventory = snapshot(f.actor.realInventory);
+            var cancel = new java.util.concurrent.atomic.AtomicBoolean(true);
+            f.packets.listen(org.bukkit.event.EventPriority.HIGHEST, event -> {
+                if (event instanceof org.bukkit.event.inventory.CraftItemEvent) event.setCancelled(cancel.get());
+            });
+            f.packets.click(0, 0, input);
+            assertTrue(assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast()).isCancelled());
+            assertEquals(grid, f.gridSnapshot());
+            assertEquals(inventory, snapshot(f.actor.realInventory));
+            assertTrue(f.menu.getCarried().isEmpty());
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty),
+                    "Native empty-stack drop calls award nothing");
+            cancel.set(false);
+            f.packets.click(0, 0, input);
+            assertFalse(f.packets.clicks.getLast().isCancelled());
+            long outputs = NativePowderSnowFixture.count(f.actor.realInventory, Material.POWDER_SNOW_BUCKET)
+                    + (f.menu.getCarried().isEmpty() ? 0 : f.menu.getCarried().getCount());
+            assertEquals(input == net.minecraft.world.inventory.ContainerInput.PICKUP ? 1 : 3, outputs);
+            assertEquals(3 - outputs, NativePowderSnowFixture.count(f.menu.craftSlots, Material.BUCKET));
+            assertEquals(3 - outputs, NativePowderSnowFixture.count(f.menu.craftSlots, Material.SNOW_BLOCK));
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void fullInventoryIncompatibleCursorAndWrongContainerRefuseNativeCompletion(int width) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            for (int slot = 0; slot < 36; slot++) f.actor.realInventory.setItem(slot, nms(Material.DIRT, 64));
+            f.menu.craftSlots.setItem(0, nms(Material.SNOW_BLOCK, 3));
+            f.menu.craftSlots.setItem(1, nms(Material.BUCKET, 3));
+            var grid = f.gridSnapshot();
+            var inventory = snapshot(f.actor.realInventory);
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.QUICK_MOVE);
+            assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast());
+            assertEquals(grid, f.gridSnapshot());
+            assertEquals(inventory, snapshot(f.actor.realInventory));
+            assertTrue(f.menu.getCarried().isEmpty());
+            f.menu.setCarried(nms(Material.DIAMOND, 1));
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.PICKUP);
+            assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast());
+            assertEquals(grid, f.gridSnapshot());
+            assertEquals(inventory, snapshot(f.actor.realInventory));
+            assertEquals(Material.DIAMOND, org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(f.menu.getCarried()).getType());
+            int events = f.packets.clicks.size();
+            f.packets.click(f.menu.containerId + 99, 0, 0, 0, net.minecraft.world.inventory.ContainerInput.PICKUP);
+            assertEquals(events, f.packets.clicks.size());
+            assertEquals(grid, f.gridSnapshot());
+            assertEquals(inventory, snapshot(f.actor.realInventory));
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty),
+                    "Native empty-stack drop calls award nothing");
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void ghostAndAutofillRelocationNeverAwardOrLoseItems(int width) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            f.actor.realInventory.setItem(0, nms(Material.SNOW_BLOCK, 3));
+            assertEquals(net.minecraft.world.inventory.RecipeBookMenu.PostPlaceAction.PLACE_GHOST_RECIPE, f.autofill(false));
+            assertEquals(3, NativePowderSnowFixture.count(f.actor.realInventory, Material.SNOW_BLOCK));
+            assertTrue(f.menu.craftSlots.isEmpty());
+            assertTrue(f.menu.resultSlots.isEmpty());
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.PICKUP);
+            assertTrue(f.menu.getCarried().isEmpty());
+            assertFalse(f.packets.clicks.getLast() instanceof org.bukkit.event.inventory.CraftItemEvent);
+            var displaced = marked(Material.DIRT, 2);
+            f.menu.craftSlots.setItem(width * width - 1, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(displaced));
+            f.actor.realInventory.setItem(1, nms(Material.BUCKET, 3));
+            assertEquals(net.minecraft.world.inventory.RecipeBookMenu.PostPlaceAction.NOTHING, f.autofill(false));
+            assertEquals(2, NativePowderSnowFixture.count(f.actor.realInventory, Material.DIRT));
+            assertTrue(snapshot(f.actor.realInventory).contains(displaced));
+            ordinaryOutput(f.menu.getResultSlot().getItem());
+            assertEquals(0, NativePowderSnowFixture.count(f.actor.realInventory, Material.POWDER_SNOW_BUCKET));
+            assertTrue(f.menu.getCarried().isEmpty());
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty),
+                    "Native empty-stack drop calls award nothing");
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void batchWithOnlyOneOutputSlotPaysOnceAndRetainsAllUncraftedInputs(int width) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            for (int slot = 0; slot < 35; slot++) f.actor.realInventory.setItem(slot, nms(Material.DIRT, 64));
+            f.menu.craftSlots.setItem(0, nms(Material.SNOW_BLOCK, 3));
+            f.menu.craftSlots.setItem(1, nms(Material.BUCKET, 3));
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.QUICK_MOVE);
+            assertInstanceOf(org.bukkit.event.inventory.CraftItemEvent.class, f.packets.clicks.getLast());
+            assertEquals(1, NativePowderSnowFixture.count(f.actor.realInventory, Material.POWDER_SNOW_BUCKET));
+            assertEquals(2, NativePowderSnowFixture.count(f.menu.craftSlots, Material.SNOW_BLOCK));
+            assertEquals(2, NativePowderSnowFixture.count(f.menu.craftSlots, Material.BUCKET));
+            assertEquals(35L * 64, NativePowderSnowFixture.count(f.actor.realInventory, Material.DIRT));
+            assertEquals(0, NativePowderSnowFixture.count(f.actor.realInventory, Material.BUCKET));
+            var remaining = f.gridSnapshot();
+            f.packets.click(0, 0, net.minecraft.world.inventory.ContainerInput.QUICK_MOVE);
+            assertEquals(remaining, f.gridSnapshot(), "Now-full output space cannot spend again");
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty));
+        }
+    }
+
+    @org.junit.jupiter.params.ParameterizedTest
+    @org.junit.jupiter.params.provider.ValueSource(ints = {2, 3})
+    void autofillCannotDiscardMetadataWhenExistingGridHasNoRelocationSpace(int width) throws Exception {
+        try (var f = new NativePowderSnowFixture(directory, width)) {
+            for (int slot = 0; slot < 36; slot++) f.actor.realInventory.setItem(slot, nms(Material.DIRT, 64));
+            f.actor.realInventory.setItem(0, nms(Material.SNOW_BLOCK, 3));
+            f.actor.realInventory.setItem(1, nms(Material.BUCKET, 3));
+            f.menu.craftSlots.setItem(0, org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(marked(Material.DIRT, 2)));
+            var before = f.gridSnapshot();
+            var inventory = snapshot(f.actor.realInventory);
+            assertEquals(net.minecraft.world.inventory.RecipeBookMenu.PostPlaceAction.NOTHING, f.autofill(false));
+            assertEquals(before, f.gridSnapshot());
+            assertEquals(inventory, snapshot(f.actor.realInventory));
+            assertTrue(f.menu.resultSlots.isEmpty());
+            assertTrue(f.menu.getCarried().isEmpty());
+            assertTrue(f.packets.drops.stream().allMatch(net.minecraft.world.item.ItemStack::isEmpty));
+        }
+    }
+
+    private static List<org.bukkit.inventory.ItemStack> snapshot(net.minecraft.world.Container container) {
+        return java.util.stream.IntStream.range(0, container.getContainerSize())
+                .mapToObj(i -> org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(container.getItem(i))).toList();
+    }
+
+    private static net.minecraft.world.item.ItemStack nms(Material material, int count) {
+        return org.bukkit.craftbukkit.inventory.CraftItemStack.asNMSCopy(new org.bukkit.inventory.ItemStack(material, count));
+    }
+
+    private static org.bukkit.inventory.ItemStack marked(Material material, int count) {
+        var item = new org.bukkit.inventory.ItemStack(material, count);
+        var meta = item.getItemMeta();
+        meta.displayName(net.kyori.adventure.text.Component.text("Keep metadata"));
+        meta.getPersistentDataContainer().set(new NamespacedKey("acceptance", "keep"),
+                org.bukkit.persistence.PersistentDataType.STRING, "unchanged");
+        item.setItemMeta(meta);
+        return item;
+    }
+
+    private static void ordinaryOutput(net.minecraft.world.item.ItemStack item) {
+        var bukkit = org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(item);
+        assertEquals(Material.POWDER_SNOW_BUCKET, bukkit.getType());
+        assertEquals(1, bukkit.getAmount());
+        assertFalse(bukkit.hasItemMeta());
+    }
+
+    @Test
+    void actualEnableRegistersExactlySnowBlockAndEmptyBucketForOneOrdinaryMiscOutput() throws Exception {
+        try (var actor = new NativeAnvilFixture(directory)) {
+            var recipe = assertInstanceOf(ShapelessRecipe.class, actor.server.getRecipe(KEY));
+            assertEquals(KEY, recipe.getKey());
+            assertEquals(List.of(List.of(Material.SNOW_BLOCK), List.of(Material.BUCKET)),
+                    recipe.getChoiceList().stream().map(choice ->
+                            assertInstanceOf(RecipeChoice.MaterialChoice.class, choice).getChoices()).toList());
+            assertEquals(CraftingBookCategory.MISC, recipe.getCategory());
+            assertEquals(Material.POWDER_SNOW_BUCKET, recipe.getResult().getType());
+            assertEquals(1, recipe.getResult().getAmount());
+            assertFalse(recipe.getResult().hasItemMeta());
+            actor.assertNoEventErrors();
+        }
+    }
+}

src/test/java/games/dmg/spigotinventoryhelper/PurpurDistributionTest.java

@@ -31,6 +31,7 @@ class PurpurDistributionTest {
             Map<?, ?> config = new Yaml().load(jar.getInputStream(jar.getJarEntry("config.yml")));
             assertEquals(Map.of("advanced-anvil-base-failure-percent", 20,
                     "advanced-anvil-risk-step-percent", 5, "advanced-anvil-max-failure-percent", 99), config);
+            assertNotNull(jar.getJarEntry("games/dmg/spigotinventoryhelper/PowderSnowRecipeRegistrar.class"));
             assertNotNull(jar.getJarEntry("games/dmg/spigotinventoryhelper/AdvancedAnvilListener.class"));
             assertNotNull(jar.getJarEntry("games/dmg/spigotinventoryhelper/AdvancedAnvilProtocolGuard.class"));
             assertNotNull(jar.getJarEntry("games/dmg/spigotinventoryhelper/NativeAnvilGeneration.class"));