d

d

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/VanillaStructureBiomes.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.core.nms.v26_2_R1;
 
+import art.arcane.iris.nativegen.NativeStructureGenerationKeys;
 import net.minecraft.core.Holder;
 import net.minecraft.core.Registry;
 import net.minecraft.core.RegistryAccess;
@@ -12,7 +13,6 @@ import net.minecraft.world.level.biome.BiomeSource;
 import net.minecraft.world.level.levelgen.structure.Structure;
 
 import java.util.LinkedHashSet;
-import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 
@@ -74,18 +74,7 @@ final class VanillaStructureBiomes {
         if (level == null) {
             throw new IllegalStateException("Minecraft server level is unavailable");
         }
-        Set<String> reachable = new LinkedHashSet<>();
         Set<String> possible = possibleBiomeKeys(source);
-        Registry<Structure> registry = level.registryAccess().lookupOrThrow(Registries.STRUCTURE);
+        return NativeStructureGenerationKeys.reachable(level, possible);
-        for (Map.Entry<ResourceKey<Structure>, Structure> entry : registry.entrySet()) {
-            for (Holder<Biome> holder : entry.getValue().biomes()) {
-                Optional<ResourceKey<Biome>> key = holder.unwrapKey();
-                if (key.isPresent() && possible.contains(key.get().identifier().toString())) {
-                    reachable.add(entry.getKey().identifier().toString());
-                    break;
-                }
-            }
-        }
-        return reachable;
     }
 }

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/nativegen/NativeStructureGenerationKeysContractTest.java

@@ -0,0 +1,60 @@
+package art.arcane.iris.nativegen;
+
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Vec3i;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.levelgen.structure.placement.RandomSpreadStructurePlacement;
+import net.minecraft.world.level.levelgen.structure.placement.RandomSpreadType;
+import net.minecraft.world.level.levelgen.structure.placement.StructurePlacement;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Optional;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class NativeStructureGenerationKeysContractTest {
+    @BeforeClass
+    public static void bootstrapMinecraft() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void reachabilityUsesEnabledActiveStructureSetsWithoutLazyPlacementGeneration() throws IOException {
+        String source = Files.readString(Path.of(
+                System.getProperty("iris.nativeStructureGenerationKeysSource")));
+
+        assertTrue(source.contains("getWorldGenSettings().options().generateStructures()"));
+        assertTrue(source.contains("getGeneratorState().possibleStructureSets()"));
+        assertTrue(source.contains("isEnabledPlacement(structureSet.placement())"));
+        assertTrue(source.contains("StructurePlacement.class.getDeclaredMethods()"));
+        assertTrue(source.contains("entry.weight() <= 0"));
+        assertTrue(source.contains("hasPossibleBiome(entry.structure().value(), possibleBiomes)"));
+        assertFalse(source.contains("getPlacementsForStructure("));
+    }
+
+    @Test
+    public void frequencyGateUsesMappedAccessorAndRejectsNonPositivePlacements() {
+        assertFalse(NativeStructureGenerationKeys.isEnabledPlacement(placement(0.0F)));
+        assertFalse(NativeStructureGenerationKeys.isEnabledPlacement(placement(-0.1F)));
+        assertFalse(NativeStructureGenerationKeys.isEnabledPlacement(placement(Float.NaN)));
+        assertTrue(NativeStructureGenerationKeys.isEnabledPlacement(placement(0.25F)));
+    }
+
+    private static RandomSpreadStructurePlacement placement(float frequency) {
+        return new RandomSpreadStructurePlacement(
+                Vec3i.ZERO,
+                StructurePlacement.FrequencyReductionMethod.DEFAULT,
+                frequency,
+                1,
+                Optional.empty(),
+                2,
+                1,
+                RandomSpreadType.LINEAR);
+    }
+}

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandFind.java

@@ -19,17 +19,23 @@
 package art.arcane.iris.core.commands;
 
 import art.arcane.iris.Iris;
-import art.arcane.iris.platform.bukkit.BukkitPlatform;
+import art.arcane.iris.core.localization.BukkitCommandMessages;
+import art.arcane.iris.core.localization.BukkitCommandMessagesExtended;
+import art.arcane.iris.core.localization.IrisLanguage;
+import art.arcane.iris.core.datapack.DatapackIngestService;
 import art.arcane.iris.core.service.ObjectStudioSaveService;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.framework.IrisStructureLocator;
 import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
-import art.arcane.iris.engine.platform.EngineBukkitOps;
 import art.arcane.iris.engine.framework.StructureReachability;
 import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisNativeStructureDecision;
 import art.arcane.iris.engine.object.IrisRegion;
 import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
+import art.arcane.iris.engine.platform.EngineBukkitOps;
+import art.arcane.iris.platform.bukkit.BukkitPlatform;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.spi.PlatformStructureHooks;
 import art.arcane.iris.util.common.director.DirectorExecutor;
 import art.arcane.iris.util.common.director.specialhandlers.ObjectHandler;
 import art.arcane.iris.util.common.director.specialhandlers.StructureHandler;
@@ -40,6 +46,7 @@ import art.arcane.volmlib.util.collection.KList;
 import art.arcane.volmlib.util.director.DirectorOrigin;
 import art.arcane.volmlib.util.director.annotations.Director;
 import art.arcane.volmlib.util.director.annotations.Param;
+import art.arcane.volmlib.util.localization.MessageArgument;
 import org.bukkit.Bukkit;
 import org.bukkit.Location;
 import org.bukkit.NamespacedKey;
@@ -49,10 +56,14 @@ import org.bukkit.entity.Player;
 import org.bukkit.generator.structure.Structure;
 import org.bukkit.util.StructureSearchResult;
 
-import art.arcane.iris.core.localization.IrisLanguage;
+import java.util.ArrayList;
-import art.arcane.iris.core.localization.BukkitCommandMessages;
+import java.util.LinkedHashMap;
-import art.arcane.volmlib.util.localization.MessageArgument;
+import java.util.LinkedHashSet;
-import art.arcane.iris.core.localization.BukkitCommandMessagesExtended;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
+
 @Director(name = "find", origin = DirectorOrigin.PLAYER, description = "Iris Find commands", descriptionKey = "iris.director.commandfind.director.iris_find_commands", aliases = "goto")
 public class CommandFind implements DirectorExecutor {
     @Director(description = "Find a biome", descriptionKey = "iris.director.commandfind.director.find_biome")
@@ -123,57 +134,66 @@ public class CommandFind implements DirectorExecutor {
             return;
         }
 
-        String structureKey = structure == null ? "" : structure.trim();
-        Structure nativeStructure = resolveNativeStructure(structureKey);
-        boolean irisReplacement = false;
-        if (nativeStructure != null) {
-            IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(
-                    e, structureKey, false);
-            if (!decision.generate()
-                    && decision.status() != NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
-                commandSender.sendMessage(C.RED + NativeStructureGenerationPolicy.generationStatusMessage(
-                        structureKey, decision.status()));
-                return;
-            }
-            irisReplacement = decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS;
-            if (irisReplacement && !IrisStructureLocator.hasNativePlacement(e, structureKey)) {
-                locateIrisStructure(e, structureKey, commandSender);
-                return;
-            }
-        }
-
-        if (nativeStructure == null && IrisStructureLocator.isPlaced(e, structureKey)) {
-            locateIrisStructure(e, structureKey, commandSender);
-            return;
-        }
-
-        if (nativeStructure == null) {
-            commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_FIND_UNKNOWN_STRUCTURE, MessageArgument.untrusted("structureKey", structureKey)));
-            return;
-        }
-        final boolean replacementLocate = irisReplacement;
-        final boolean explicitNativePlacement = IrisStructureLocator.hasNativePlacement(
-                e, structureKey);
-
         Player target = player();
         if (target == null) {
             commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_FIND_RUN_THIS_GAME_TELEPORT_STRUCTURE));
             return;
         }
 
+        String structureKey = structure == null ? "" : structure.trim();
+        Structure nativeStructure = resolveNativeStructure(structureKey);
+        boolean registered = nativeStructure != null;
+        IrisNativeStructureDecision decision = registered
+                ? NativeStructureGenerationPolicy.resolve(e, structureKey, false)
+                : null;
+        boolean nativePlacement = IrisStructureLocator.hasNativePlacement(e, structureKey);
+        boolean locatableNativePlacement = IrisStructureLocator.hasLocatableNativePlacement(e, structureKey);
+        boolean locatableEditablePlacement = IrisStructureLocator.hasLocatableEditablePlacement(e, structureKey);
         World targetWorld = target.getWorld();
+        boolean nativeGenerationEnabled = targetWorld.canGenerateStructures();
+        boolean requiresReachability = registered && decision.generate()
+                && decision.status() != NativeStructureGenerationStatus.REPLACED_BY_IRIS
+                && nativeGenerationEnabled;
+        boolean reachable = !requiresReachability || StructureReachability.isReachable(e, structureKey);
+        StructureLookupRoute route = selectStructureLookupRoute(
+                registered, decision, nativePlacement, locatableNativePlacement,
+                locatableEditablePlacement, nativeGenerationEnabled, reachable);
+
+        if (route == StructureLookupRoute.UNKNOWN) {
+            commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_FIND_UNKNOWN_STRUCTURE, MessageArgument.untrusted("structureKey", structureKey)));
+            return;
+        }
+        if (route == StructureLookupRoute.POLICY_DISABLED) {
+            commandSender.sendMessage(C.RED + NativeStructureGenerationPolicy.generationStatusMessage(
+                    structureKey, decision.status()));
+            return;
+        }
+        if (route == StructureLookupRoute.NO_ACTIVE_PLACEMENT) {
+            commandSender.sendMessage(C.YELLOW + structureKey
+                    + " has no active placement in this world.");
+            return;
+        }
+        if (route == StructureLookupRoute.WORLD_DISABLED) {
+            commandSender.sendMessage(C.YELLOW + structureKey
+                    + " cannot generate because native structure generation is disabled for this world.");
+            return;
+        }
+        if (route == StructureLookupRoute.UNREACHABLE) {
+            KList<String> miss = StructureReachability.missingBiomeKeys(e, structureKey);
+            commandSender.sendMessage(C.YELLOW + structureKey
+                    + " cannot generate in this world (its required biomes are not produced by this pack"
+                    + (miss.isEmpty() ? "" : ": needs " + String.join("/", miss)) + ").");
+            return;
+        }
+        if (route == StructureLookupRoute.IRIS) {
+            locateIrisStructure(e, structureKey, commandSender);
+            return;
+        }
+
         Location origin = target.getLocation();
         commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_FIND_LOCATING, MessageArgument.untrusted("structureKey", structureKey)));
         J.s(() -> {
             try {
-                if (!replacementLocate && !explicitNativePlacement
-                        && !StructureReachability.isReachable(e, structureKey)) {
-                    KList<String> miss = StructureReachability.missingBiomeKeys(e, structureKey);
-                    sendStructureMessage(target, commandSender,
-                            C.YELLOW + structureKey + " cannot generate in this world (its required biomes are not produced by this pack"
-                                    + (miss.isEmpty() ? "" : ": needs " + String.join("/", miss)) + ").");
-                    return;
-                }
                 StructureSearchResult result = targetWorld.locateNearestStructure(
                         origin, nativeStructure, 100, false);
                 if (result == null || result.getLocation() == null) {
@@ -191,6 +211,365 @@ public class CommandFind implements DirectorExecutor {
         });
     }
 
+    @Director(description = "Print every structure excluded from /iris goto and its rejection reason to the server console", sync = true)
+    public void unregistered() {
+        VolmitSender commandSender = sender();
+        if (commandSender == null) {
+            Iris.reportError("Structure exclusion report started without a command sender context.",
+                    new IllegalStateException("Missing command sender context"));
+            return;
+        }
+        Engine activeEngine = engine();
+        if (activeEngine == null) {
+            commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_FIND_NOT_IRIS_WORLD));
+            return;
+        }
+        Player target = player();
+        if (target == null) {
+            commandSender.sendMessage(C.RED + "Run this command from the Iris world to inspect its structures.");
+            return;
+        }
+
+        StructureExclusionReport snapshot;
+        try {
+            snapshot = collectStructureExclusions(
+                    activeEngine, target.getWorld().canGenerateStructures());
+        } catch (Throwable error) {
+            commandSender.sendMessage(C.RED + "Could not build the structure exclusion report; see the server console.");
+            Iris.reportError("Could not snapshot /iris goto unregistered report for world '"
+                    + target.getWorld().getName() + "'.", error);
+            return;
+        }
+
+        String worldName = target.getWorld().getName();
+        J.a(() -> {
+            try {
+                StructureExclusionReport report = includeManagedDatapackStructures(
+                        snapshot, DatapackIngestService.installed());
+                printStructureExclusionReport(worldName, report);
+                sendStructureMessage(target, commandSender, C.GREEN + "Printed " + report.entries().size()
+                        + " non-generating structure candidate(s) and their reasons to the server console. "
+                        + "This was an eligibility check; no chunks were searched.");
+            } catch (Throwable error) {
+                sendStructureMessage(target, commandSender,
+                        C.RED + "Could not finish the structure exclusion report; see the server console.");
+                Iris.reportError("Could not finish /iris goto unregistered report for world '"
+                        + worldName + "'.", error);
+            }
+        });
+    }
+
+    private static StructureExclusionReport collectStructureExclusions(
+            Engine engine, boolean nativeGenerationEnabled) {
+        PlatformStructureHooks structureHooks = IrisPlatforms.get().structureHooks();
+        Map<String, String> registeredKeys = distinctStructureKeys(structureHooks.structureKeys());
+        Set<String> reachableKeys = StructureReachability.reachableKeys(engine);
+        Set<String> possibleBiomeKeys = normalizedStructureKeys(
+                structureHooks.possibleBiomeKeys(engine.getWorld().platformWorld()));
+        List<StructureExclusion> exclusions = new ArrayList<>();
+        int registeredExcluded = 0;
+
+        for (Map.Entry<String, String> entry : registeredKeys.entrySet()) {
+            String normalizedKey = entry.getKey();
+            String key = entry.getValue();
+            IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(engine, key, false);
+            boolean nativePlacement = IrisStructureLocator.hasNativePlacement(engine, key);
+            boolean locatableNativePlacement = IrisStructureLocator.hasLocatableNativePlacement(engine, key);
+            boolean locatableEditablePlacement = IrisStructureLocator.hasLocatableEditablePlacement(engine, key);
+            StructureLookupRoute route = selectStructureLookupRoute(
+                    true, decision, nativePlacement, locatableNativePlacement,
+                    locatableEditablePlacement, nativeGenerationEnabled,
+                    reachableKeys.contains(normalizedKey));
+            if (route == StructureLookupRoute.IRIS || route == StructureLookupRoute.NATIVE) {
+                continue;
+            }
+            List<String> requiredBiomes = needsNativeReachabilityReason(route, decision)
+                    ? structureHooks.structureBiomeKeys(key)
+                    : List.of();
+            exclusions.add(new StructureExclusion(
+                    StructureExclusionKind.EXCLUDED, key, null,
+                    describeStructureExclusion(
+                            route, key, decision.status(), nativePlacement,
+                            requiredBiomes, possibleBiomeKeys)));
+            registeredExcluded++;
+        }
+
+        int configuredUnregistered = 0;
+        Set<String> configuredUnregisteredKeys = new LinkedHashSet<>();
+        for (String configuredKey : IrisStructureLocator.placedKeys(engine)) {
+            String normalizedKey = normalizeStructureKey(configuredKey);
+            if (normalizedKey.isEmpty()
+                    || registeredKeys.containsKey(normalizedKey)
+                    || !IrisStructureLocator.hasNativePlacement(engine, configuredKey)
+                    || !configuredUnregisteredKeys.add(normalizedKey)) {
+                continue;
+            }
+            exclusions.add(new StructureExclusion(
+                    StructureExclusionKind.UNREGISTERED, configuredKey, null,
+                    describeConfiguredUnregisteredNative(
+                            IrisStructureLocator.hasLocatableNativePlacement(engine, configuredKey))));
+            configuredUnregistered++;
+        }
+
+        int editableUnplaced = 0;
+        Set<String> unplacedEditableKeys = new LinkedHashSet<>();
+        Set<String> locatableEditableKeys = normalizedStructureKeys(
+                IrisStructureLocator.locatableEditableKeys(engine));
+        for (String editableKey : engine.getData().getStructureLoader().getPossibleKeys()) {
+            String normalizedKey = normalizeStructureKey(editableKey);
+            if (!isUnplacedEditableCandidate(
+                    normalizedKey, registeredKeys.keySet(), locatableEditableKeys,
+                    IrisStructureLocator.hasNativePlacement(engine, editableKey))
+                    || !unplacedEditableKeys.add(normalizedKey)) {
+                continue;
+            }
+            boolean configuredPlacement = IrisStructureLocator.hasEditablePlacement(engine, editableKey);
+            String reason = configuredPlacement
+                    ? "editable Iris structure has a configured placement, but no matching placement is active "
+                    + "because its density is not positive or its Y band does not intersect this world"
+                    : "editable Iris structure exists in this pack, but no structure placement references it";
+            exclusions.add(new StructureExclusion(
+                    StructureExclusionKind.UNPLACED, editableKey, null, reason));
+            editableUnplaced++;
+        }
+
+        Set<String> configuredImportUrls = normalizedImportUrls(
+                engine.getDimension().getDatapackImports());
+        return new StructureExclusionReport(
+                List.copyOf(exclusions), Set.copyOf(registeredKeys.keySet()),
+                configuredImportUrls, registeredExcluded, configuredUnregistered,
+                editableUnplaced, 0);
+    }
+
+    static boolean isUnplacedEditableCandidate(
+            String normalizedKey, Set<String> registeredKeys,
+            Set<String> locatableEditableKeys, boolean nativePlacement) {
+        return normalizedKey != null
+                && !normalizedKey.isEmpty()
+                && !registeredKeys.contains(normalizedKey)
+                && !locatableEditableKeys.contains(normalizedKey)
+                && !nativePlacement;
+    }
+
+    private static StructureExclusionReport includeManagedDatapackStructures(
+            StructureExclusionReport snapshot, List<DatapackIngestService.Entry> installedEntries) {
+        Map<String, ManagedDatapackStructure> unregisteredStructures = new LinkedHashMap<>();
+        for (DatapackIngestService.Entry entry : installedEntries) {
+            String importUrl = normalizeImportUrl(entry.url);
+            if (importUrl.isEmpty() || !snapshot.configuredImportUrls().contains(importUrl)) {
+                continue;
+            }
+            String sourceId = entry.id == null || entry.id.isBlank() ? "unknown" : entry.id.trim();
+            List<String> structureKeys = entry.structureKeys == null ? List.of() : entry.structureKeys;
+            for (String key : structureKeys) {
+                String normalizedKey = normalizeStructureKey(key);
+                if (normalizedKey.isEmpty() || snapshot.registeredKeys().contains(normalizedKey)) {
+                    continue;
+                }
+                ManagedDatapackStructure managed = unregisteredStructures.computeIfAbsent(
+                        normalizedKey, ignored -> new ManagedDatapackStructure(key.trim()));
+                managed.sourceIds().add(sourceId);
+            }
+        }
+
+        List<StructureExclusion> entries = new ArrayList<>();
+        int configuredUnregistered = snapshot.configuredUnregistered();
+        for (StructureExclusion exclusion : snapshot.entries()) {
+            boolean replacedByManagedSource = exclusion.kind() == StructureExclusionKind.UNREGISTERED
+                    && unregisteredStructures.containsKey(normalizeStructureKey(exclusion.key()));
+            if (replacedByManagedSource) {
+                configuredUnregistered--;
+                continue;
+            }
+            entries.add(exclusion);
+        }
+        for (ManagedDatapackStructure managed : unregisteredStructures.values()) {
+            entries.add(new StructureExclusion(
+                    StructureExclusionKind.UNREGISTERED, managed.key(),
+                    String.join(",", managed.sourceIds()),
+                    "declared by an Iris-managed datapack but absent from the live registry; "
+                            + "restart, enablement, or datapack validation may be required"));
+        }
+        sortStructureExclusions(entries);
+        return new StructureExclusionReport(
+                List.copyOf(entries), snapshot.registeredKeys(), snapshot.configuredImportUrls(),
+                snapshot.registeredExcluded(), Math.max(0, configuredUnregistered),
+                snapshot.editableUnplaced(), unregisteredStructures.size());
+    }
+
+    private static void printStructureExclusionReport(
+            String worldName, StructureExclusionReport report) {
+        Iris.info("Iris goto unregistered report for world '%s': %d non-generating structure candidate(s).",
+                worldName, report.entries().size());
+        for (StructureExclusion exclusion : report.entries()) {
+            String source = exclusion.source() == null
+                    ? ""
+                    : " (source " + exclusion.source() + ")";
+            Iris.info("[%s] %s%s: %s",
+                    exclusion.kind().label(), exclusion.key(), source, exclusion.reason());
+        }
+        Iris.info("Iris goto unregistered summary: %d registered key(s) excluded, "
+                        + "%d managed datapack key(s) unregistered, %d configured native key(s) unregistered, "
+                        + "%d editable Iris structure(s) unplaced.",
+                report.registeredExcluded(), report.managedUnregistered(),
+                report.configuredUnregistered(), report.editableUnplaced());
+        Iris.info("Eligibility report only; no chunks were searched and existing generated starts were not scanned.");
+    }
+
+    private static boolean needsNativeReachabilityReason(
+            StructureLookupRoute route, IrisNativeStructureDecision decision) {
+        return route == StructureLookupRoute.UNREACHABLE
+                || route == StructureLookupRoute.NO_ACTIVE_PLACEMENT && decision.generate();
+    }
+
+    static String describeStructureExclusion(
+            StructureLookupRoute route, String key, NativeStructureGenerationStatus status,
+            boolean nativePlacement, List<String> requiredBiomes, Set<String> possibleBiomeKeys) {
+        return switch (route) {
+            case UNKNOWN -> "the key is not registered by the active server/datapack";
+            case POLICY_DISABLED -> NativeStructureGenerationPolicy.generationStatusMessage(key, status);
+            case WORLD_DISABLED -> "native structure generation is disabled for this world";
+            case UNREACHABLE -> nativeReachabilityReason(requiredBiomes, possibleBiomeKeys);
+            case NO_ACTIVE_PLACEMENT -> {
+                String placementType = nativePlacement
+                        ? "configured nativeStructures placement"
+                        : "configured Iris replacement";
+                String reason = placementType + " is inactive: no matching placement has positive density "
+                        + "when density-based and a Y band intersecting this world";
+                if (status == NativeStructureGenerationStatus.GENERATE_NATIVE) {
+                    reason += "; the native route is also inactive because "
+                            + nativeReachabilityReason(requiredBiomes, possibleBiomeKeys);
+                }
+                yield reason;
+            }
+            case IRIS, NATIVE -> throw new IllegalArgumentException(
+                    "Active structure route cannot be described as excluded: " + route);
+        };
+    }
+
+    static String nativeReachabilityReason(
+            List<String> requiredBiomes, Set<String> possibleBiomeKeys) {
+        if (requiredBiomes == null || requiredBiomes.isEmpty()) {
+            return "its resolved biome filter is empty";
+        }
+        Set<String> possible = possibleBiomeKeys == null ? Set.of() : possibleBiomeKeys;
+        for (String requiredBiome : requiredBiomes) {
+            if (possible.contains(normalizeStructureKey(requiredBiome))) {
+                return "no active positive-weight, positive-frequency structure-set entry includes it in this world";
+            }
+        }
+        return "this pack does not produce any of its required biome(s): "
+                + String.join("/", requiredBiomes);
+    }
+
+    static String describeConfiguredUnregisteredNative(boolean locatablePlacement) {
+        String reason = "configured in nativeStructures, but the key is not registered by the active "
+                + "server/datapack, so Minecraft cannot create its native structure start";
+        return locatablePlacement
+                ? reason
+                : reason + "; its Iris placement is also inactive because no matching placement has positive "
+                + "density when density-based and a Y band intersecting this world";
+    }
+
+    private static Map<String, String> distinctStructureKeys(List<String> keys) {
+        Map<String, String> distinctKeys = new LinkedHashMap<>();
+        for (String key : keys) {
+            String normalizedKey = normalizeStructureKey(key);
+            if (!normalizedKey.isEmpty()) {
+                distinctKeys.putIfAbsent(normalizedKey, key.trim());
+            }
+        }
+        return distinctKeys;
+    }
+
+    private static Set<String> normalizedStructureKeys(Iterable<String> keys) {
+        Set<String> normalizedKeys = new LinkedHashSet<>();
+        if (keys == null) {
+            return normalizedKeys;
+        }
+        for (String key : keys) {
+            String normalizedKey = normalizeStructureKey(key);
+            if (!normalizedKey.isEmpty()) {
+                normalizedKeys.add(normalizedKey);
+            }
+        }
+        return normalizedKeys;
+    }
+
+    private static Set<String> normalizedImportUrls(Iterable<String> urls) {
+        Set<String> normalizedUrls = new LinkedHashSet<>();
+        if (urls == null) {
+            return normalizedUrls;
+        }
+        for (String url : urls) {
+            String normalizedUrl = normalizeImportUrl(url);
+            if (!normalizedUrl.isEmpty()) {
+                normalizedUrls.add(normalizedUrl);
+            }
+        }
+        return Set.copyOf(normalizedUrls);
+    }
+
+    private static String normalizeImportUrl(String url) {
+        return url == null ? "" : url.trim();
+    }
+
+    private static void sortStructureExclusions(List<StructureExclusion> exclusions) {
+        exclusions.sort((left, right) -> {
+            int kindComparison = left.kind().compareTo(right.kind());
+            return kindComparison == 0
+                    ? left.key().compareToIgnoreCase(right.key())
+                    : kindComparison;
+        });
+    }
+
+    private static String normalizeStructureKey(String key) {
+        return key == null ? "" : key.trim().toLowerCase(Locale.ROOT);
+    }
+
+    static StructureLookupRoute selectStructureLookupRoute(
+            boolean registered, IrisNativeStructureDecision decision, boolean nativePlacement,
+            boolean locatableNativePlacement, boolean locatableEditablePlacement,
+            boolean nativeGenerationEnabled, boolean reachable) {
+        if (!registered) {
+            return !nativePlacement && locatableEditablePlacement
+                    ? StructureLookupRoute.IRIS
+                    : StructureLookupRoute.UNKNOWN;
+        }
+        if (decision == null) {
+            throw new IllegalArgumentException("Registered structure lookup requires a generation decision");
+        }
+        if (!decision.generate()
+                && decision.status() != NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+            return StructureLookupRoute.POLICY_DISABLED;
+        }
+        if (decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+            if (!nativePlacement) {
+                return locatableEditablePlacement
+                        ? StructureLookupRoute.IRIS
+                        : StructureLookupRoute.NO_ACTIVE_PLACEMENT;
+            }
+            if (!nativeGenerationEnabled) {
+                return StructureLookupRoute.WORLD_DISABLED;
+            }
+            return locatableNativePlacement
+                    ? StructureLookupRoute.NATIVE
+                    : StructureLookupRoute.NO_ACTIVE_PLACEMENT;
+        }
+        if (!nativeGenerationEnabled) {
+            return StructureLookupRoute.WORLD_DISABLED;
+        }
+        if (nativePlacement && locatableNativePlacement) {
+            return StructureLookupRoute.NATIVE;
+        }
+        if (reachable) {
+            return StructureLookupRoute.NATIVE;
+        }
+        return nativePlacement
+                ? StructureLookupRoute.NO_ACTIVE_PLACEMENT
+                : StructureLookupRoute.UNREACHABLE;
+    }
+
     private static Structure resolveNativeStructure(String structureKey) {
         Registry<Structure> structureRegistry = Bukkit.getRegistry(Structure.class);
         if (structureRegistry == null) {
@@ -314,4 +693,46 @@ public class CommandFind implements DirectorExecutor {
     private void sendStructureMessage(Player target, VolmitSender commandSender, String message) {
         J.runEntity(target, () -> commandSender.sendMessage(message));
     }
+
+    enum StructureLookupRoute {
+        UNKNOWN,
+        POLICY_DISABLED,
+        NO_ACTIVE_PLACEMENT,
+        WORLD_DISABLED,
+        UNREACHABLE,
+        IRIS,
+        NATIVE
+    }
+
+    private enum StructureExclusionKind {
+        UNREGISTERED("unregistered"),
+        EXCLUDED("excluded"),
+        UNPLACED("unplaced");
+
+        private final String label;
+
+        StructureExclusionKind(String label) {
+            this.label = label;
+        }
+
+        private String label() {
+            return label;
+        }
+    }
+
+    private record StructureExclusion(
+            StructureExclusionKind kind, String key, String source, String reason) {
+    }
+
+    private record StructureExclusionReport(
+            List<StructureExclusion> entries, Set<String> registeredKeys,
+            Set<String> configuredImportUrls, int registeredExcluded,
+            int configuredUnregistered, int editableUnplaced, int managedUnregistered) {
+    }
+
+    private record ManagedDatapackStructure(String key, Set<String> sourceIds) {
+        private ManagedDatapackStructure(String key) {
+            this(key, new LinkedHashSet<>());
+        }
+    }
 }

adapters/bukkit/plugin/src/test/java/art/arcane/iris/core/commands/IrisStructureLocateCommandContractTest.java

@@ -1,12 +1,15 @@
 package art.arcane.iris.core.commands;
 
 import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
+import art.arcane.iris.engine.object.IrisNativeStructureDecision;
 import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
 import org.junit.Test;
 
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.List;
+import java.util.Set;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -25,32 +28,189 @@ public class IrisStructureLocateCommandContractTest {
     }
 
     @Test
-    public void findRoutesRegisteredReplacementThroughPersistedNativeLocate() throws IOException {
+    public void findRoutesOnlyActiveWorldStructures() throws IOException {
         String source = Files.readString(Path.of(System.getProperty("iris.commandFindSource")));
         int methodStart = source.indexOf("public void structure(");
-        int methodEnd = source.indexOf("private static Structure resolveNativeStructure", methodStart);
+        int methodEnd = source.indexOf("static StructureLookupRoute selectStructureLookupRoute", methodStart);
         String method = source.substring(methodStart, methodEnd);
         int nativeResolution = method.indexOf("resolveNativeStructure(structureKey)");
         int policyResolution = method.indexOf("NativeStructureGenerationPolicy.resolve(", nativeResolution);
-        int replacementCheck = method.indexOf(
+        int nativeLocatableCheck = method.indexOf(
-                "decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS", policyResolution);
+                "IrisStructureLocator.hasLocatableNativePlacement(e, structureKey)", policyResolution);
-        int genericIrisLookup = method.indexOf(
+        int editableLocatableCheck = method.indexOf(
-                "nativeStructure == null && IrisStructureLocator.isPlaced(e, structureKey)", replacementCheck);
+                "IrisStructureLocator.hasLocatableEditablePlacement(e, structureKey)", nativeLocatableCheck);
-        int replacementLocate = method.indexOf("final boolean replacementLocate = irisReplacement", genericIrisLookup);
+        int worldGenerationCheck = method.indexOf("targetWorld.canGenerateStructures()", editableLocatableCheck);
-        int nativeLocate = method.indexOf("targetWorld.locateNearestStructure(", genericIrisLookup);
+        int routeResolution = method.indexOf("selectStructureLookupRoute(", editableLocatableCheck);
+        int nativeLocate = method.indexOf("targetWorld.locateNearestStructure(", routeResolution);
+
         assertTrue(nativeResolution >= 0);
         assertTrue(policyResolution > nativeResolution);
-        assertTrue(replacementCheck > policyResolution);
+        assertTrue(nativeLocatableCheck > policyResolution);
-        assertTrue(genericIrisLookup > replacementCheck);
+        assertTrue(editableLocatableCheck > nativeLocatableCheck);
-        assertTrue(replacementLocate > genericIrisLookup);
+        assertTrue(worldGenerationCheck > editableLocatableCheck);
-        assertTrue(nativeLocate > policyResolution);
+        assertTrue(routeResolution > editableLocatableCheck);
-        assertTrue(method.contains("irisReplacement && !IrisStructureLocator.hasNativePlacement"));
+        assertTrue(nativeLocate > routeResolution);
-        assertTrue(method.contains("!replacementLocate && !explicitNativePlacement"));
+        assertFalse(method.contains("IrisStructureLocator.isPlaced(e, structureKey)"));
-        assertTrue(method.contains("&& !StructureReachability.isReachable"));
-        assertTrue(method.contains("decision.status() != NativeStructureGenerationStatus.REPLACED_BY_IRIS"));
         assertFalse(method.contains("NativeStructureLocateCapability"));
     }
 
+    @Test
+    public void findRejectsUnregisteredNativeAndDormantPlacements() {
+        assertEquals(CommandFind.StructureLookupRoute.UNKNOWN,
+                CommandFind.selectStructureLookupRoute(
+                        false, null, true, true, false, true, true));
+        assertEquals(CommandFind.StructureLookupRoute.UNKNOWN,
+                CommandFind.selectStructureLookupRoute(
+                        false, null, false, false, false, true, true));
+        assertEquals(CommandFind.StructureLookupRoute.NO_ACTIVE_PLACEMENT,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.REPLACED_BY_IRIS),
+                        false, false, false, true, true));
+        assertEquals(CommandFind.StructureLookupRoute.NO_ACTIVE_PLACEMENT,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.GENERATE_NATIVE),
+                        true, false, false, true, false));
+    }
+
+    @Test
+    public void findAllowsLocatableEditablePlacementsWithoutNativeGeneration() {
+        assertEquals(CommandFind.StructureLookupRoute.IRIS,
+                CommandFind.selectStructureLookupRoute(
+                        false, null, false, false, true, false, false));
+        assertEquals(CommandFind.StructureLookupRoute.IRIS,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.REPLACED_BY_IRIS),
+                        false, false, true, false, false));
+    }
+
+    @Test
+    public void findRequiresWorldGenerationAndReachabilityForNativeRoutes() {
+        assertEquals(CommandFind.StructureLookupRoute.WORLD_DISABLED,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.REPLACED_BY_IRIS),
+                        true, true, false, false, true));
+        assertEquals(CommandFind.StructureLookupRoute.WORLD_DISABLED,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.GENERATE_NATIVE),
+                        false, false, false, false, true));
+        assertEquals(CommandFind.StructureLookupRoute.UNREACHABLE,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.GENERATE_NATIVE),
+                        false, false, false, true, false));
+        assertEquals(CommandFind.StructureLookupRoute.NATIVE,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.GENERATE_NATIVE),
+                        true, true, false, true, false));
+        assertEquals(CommandFind.StructureLookupRoute.NATIVE,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.GENERATE_NATIVE),
+                        true, false, false, true, true));
+    }
+
+    @Test
+    public void findHonorsPackDisableBeforePlacementRouting() {
+        assertEquals(CommandFind.StructureLookupRoute.POLICY_DISABLED,
+                CommandFind.selectStructureLookupRoute(
+                        true, decision(NativeStructureGenerationStatus.DISABLED_BY_PACK),
+                        false, false, true, true, true));
+    }
+
+    @Test
+    public void unregisteredDiagnosticExplainsEveryRejectedRoute() {
+        assertEquals(
+                "Native structure minecraft:village is disabled by this dimension's importedStructures settings.",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.POLICY_DISABLED, "minecraft:village",
+                        NativeStructureGenerationStatus.DISABLED_BY_PACK,
+                        false, List.of(), Set.of()));
+        assertEquals(
+                "native structure generation is disabled for this world",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.WORLD_DISABLED, "minecraft:village",
+                        NativeStructureGenerationStatus.GENERATE_NATIVE,
+                        false, List.of(), Set.of()));
+        assertEquals(
+                "its resolved biome filter is empty",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.UNREACHABLE, "towns_and_towers:exclusive",
+                        NativeStructureGenerationStatus.GENERATE_NATIVE,
+                        false, List.of(), Set.of()));
+        assertEquals(
+                "this pack does not produce any of its required biome(s): terralith:alpine_grove/bwg:aspen_boreal",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.UNREACHABLE, "towns_and_towers:exclusive",
+                        NativeStructureGenerationStatus.GENERATE_NATIVE,
+                        false, List.of("terralith:alpine_grove", "bwg:aspen_boreal"),
+                        Set.of("minecraft:plains")));
+        assertEquals(
+                "no active positive-weight, positive-frequency structure-set entry includes it in this world",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.UNREACHABLE, "example:dormant",
+                        NativeStructureGenerationStatus.GENERATE_NATIVE,
+                        false, List.of("minecraft:plains"), Set.of("minecraft:plains")));
+        assertEquals(
+                "no active positive-weight, positive-frequency structure-set entry includes it in this world",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.UNREACHABLE, "example:partial_overlap",
+                        NativeStructureGenerationStatus.GENERATE_NATIVE,
+                        false, List.of("minecraft:plains", "mod:absent"), Set.of("minecraft:plains")));
+    }
+
+    @Test
+    public void unregisteredDiagnosticExplainsInactiveAndMissingNativePlacements() {
+        assertEquals(
+                "configured Iris replacement is inactive: no matching placement has positive density when "
+                        + "density-based and a Y band intersecting this world",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.NO_ACTIVE_PLACEMENT, "example:replacement",
+                        NativeStructureGenerationStatus.REPLACED_BY_IRIS,
+                        false, List.of(), Set.of()));
+        assertEquals(
+                "configured nativeStructures placement is inactive: no matching placement has positive density "
+                        + "when density-based and a Y band intersecting this world; the native route is also "
+                        + "inactive because its resolved biome filter is empty",
+                CommandFind.describeStructureExclusion(
+                        CommandFind.StructureLookupRoute.NO_ACTIVE_PLACEMENT, "example:native",
+                        NativeStructureGenerationStatus.GENERATE_NATIVE,
+                        true, List.of(), Set.of()));
+        assertTrue(CommandFind.describeConfiguredUnregisteredNative(true)
+                .contains("key is not registered by the active server/datapack"));
+        assertFalse(CommandFind.describeConfiguredUnregisteredNative(true)
+                .contains("Iris placement is also inactive"));
+        assertTrue(CommandFind.describeConfiguredUnregisteredNative(false)
+                .contains("Iris placement is also inactive"));
+    }
+
+    @Test
+    public void unplacedEditableDiagnosticDefersToRegistryAndNativeCategories() {
+        assertTrue(CommandFind.isUnplacedEditableCandidate(
+                "pack:editable", Set.of(), Set.of(), false));
+        assertFalse(CommandFind.isUnplacedEditableCandidate(
+                "pack:editable", Set.of("pack:editable"), Set.of(), false));
+        assertFalse(CommandFind.isUnplacedEditableCandidate(
+                "pack:editable", Set.of(), Set.of("pack:editable"), false));
+        assertFalse(CommandFind.isUnplacedEditableCandidate(
+                "pack:editable", Set.of(), Set.of(), true));
+    }
+
+    @Test
+    public void unregisteredDiagnosticPrintsDetailsOnlyToConsole() throws IOException {
+        String source = Files.readString(Path.of(System.getProperty("iris.commandFindSource")));
+        int methodStart = source.indexOf("public void unregistered()");
+        int methodEnd = source.indexOf("private static StructureExclusionReport", methodStart);
+        String method = source.substring(methodStart, methodEnd);
+
+        assertTrue(methodStart >= 0);
+        assertTrue(source.contains("Iris.info(\"[%s] %s%s: %s\""));
+        assertTrue(method.contains("non-generating structure candidate(s) and their reasons to the server console"));
+        assertTrue(method.contains("no chunks were searched"));
+        assertTrue(method.indexOf("DatapackIngestService.installed()") > method.indexOf("J.a(() ->"));
+        assertTrue(source.contains("engine.getDimension().getDatapackImports()"));
+        assertTrue(source.contains("snapshot.configuredImportUrls().contains(importUrl)"));
+        assertTrue(source.contains("engine.getData().getStructureLoader().getPossibleKeys()"));
+        assertFalse(method.contains("commandSender.sendMessage(exclusion"));
+    }
+
     @Test
     public void findNativePolicyMessagesMatchModdedDiagnostics() {
         assertEquals(
@@ -95,4 +255,9 @@ public class IrisStructureLocateCommandContractTest {
         assertTrue(reachabilityGuard > nativeRequirement);
         assertTrue(reachabilityLookup > reachabilityGuard);
     }
+
+    private static IrisNativeStructureDecision decision(NativeStructureGenerationStatus status) {
+        return new IrisNativeStructureDecision(
+                status, 0, null, false, false, null, null);
+    }
 }

adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeStructureGenerationKeys.java

@@ -0,0 +1,117 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.nativegen;
+
+import net.minecraft.core.Holder;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.levelgen.structure.Structure;
+import net.minecraft.world.level.levelgen.structure.StructureSet;
+import net.minecraft.world.level.levelgen.structure.placement.StructurePlacement;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+
+public final class NativeStructureGenerationKeys {
+    private static final Method FREQUENCY_METHOD = resolveFrequencyMethod();
+
+    private NativeStructureGenerationKeys() {
+    }
+
+    public static Set<String> reachable(ServerLevel level, Set<String> possibleBiomeKeys) {
+        ServerLevel activeLevel = Objects.requireNonNull(level, "Native structure reachability requires a level");
+        Set<String> possibleBiomes = Objects.requireNonNull(
+                possibleBiomeKeys, "Native structure reachability requires possible biome keys");
+        if (!activeLevel.getServer().getWorldGenSettings().options().generateStructures()) {
+            return Collections.emptySet();
+        }
+
+        Set<String> keys = new LinkedHashSet<>();
+        List<Holder<StructureSet>> structureSets =
+                activeLevel.getChunkSource().getGeneratorState().possibleStructureSets();
+        for (Holder<StructureSet> structureSetHolder : structureSets) {
+            StructureSet structureSet = structureSetHolder.value();
+            if (!isEnabledPlacement(structureSet.placement())) {
+                continue;
+            }
+            for (StructureSet.StructureSelectionEntry entry : structureSet.structures()) {
+                if (entry.weight() <= 0 || !hasPossibleBiome(entry.structure().value(), possibleBiomes)) {
+                    continue;
+                }
+                Optional<ResourceKey<Structure>> key = entry.structure().unwrapKey();
+                key.ifPresent(resourceKey -> keys.add(resourceKey.identifier().toString()));
+            }
+        }
+        return Collections.unmodifiableSet(keys);
+    }
+
+    static boolean hasPossibleBiome(Structure structure, Set<String> possibleBiomeKeys) {
+        for (Holder<Biome> holder : structure.biomes()) {
+            Optional<ResourceKey<Biome>> key = holder.unwrapKey();
+            if (key.isPresent() && possibleBiomeKeys.contains(key.get().identifier().toString())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    static boolean isEnabledPlacement(StructurePlacement placement) {
+        return placementFrequency(placement) > 0.0F;
+    }
+
+    private static float placementFrequency(StructurePlacement placement) {
+        StructurePlacement activePlacement = Objects.requireNonNull(
+                placement, "Native structure placement frequency requires a placement");
+        try {
+            return ((Float) FREQUENCY_METHOD.invoke(activePlacement)).floatValue();
+        } catch (ReflectiveOperationException error) {
+            throw new IllegalStateException(
+                    "Unable to read native structure placement frequency from "
+                            + activePlacement.getClass().getName(), error);
+        }
+    }
+
+    private static Method resolveFrequencyMethod() {
+        Method frequencyMethod = null;
+        for (Method method : StructurePlacement.class.getDeclaredMethods()) {
+            if (Modifier.isStatic(method.getModifiers())
+                    || method.getParameterCount() != 0
+                    || method.getReturnType() != float.class) {
+                continue;
+            }
+            if (frequencyMethod != null) {
+                throw new IllegalStateException(
+                        "Native structure placement exposes multiple zero-argument float accessors");
+            }
+            frequencyMethod = method;
+        }
+        if (frequencyMethod == null || !frequencyMethod.trySetAccessible()) {
+            throw new IllegalStateException(
+                    "Native structure placement frequency accessor is unavailable");
+        }
+        return frequencyMethod;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedStructureHooks.java

@@ -19,6 +19,7 @@
 package art.arcane.iris.modded;
 
 import art.arcane.iris.nativegen.NativeStructureGenerationException;
+import art.arcane.iris.nativegen.NativeStructureGenerationKeys;
 import art.arcane.iris.nativegen.NativeStructureFactory;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.spi.PlatformStructureHooks;
@@ -225,22 +226,15 @@ public final class ModdedStructureHooks implements PlatformStructureHooks {
 
     @Override
     public List<String> reachableStructureKeys(PlatformWorld world) {
-        List<String> keys = new ArrayList<>();
         ServerLevel level = requireLevel(world, "resolve reachable structures");
         try {
             BiomeSource source = level.getChunkSource().getGenerator().getBiomeSource();
             Set<String> possibleBiomes = possibleBiomeKeys(source);
-            Registry<Structure> registry = level.registryAccess().lookupOrThrow(Registries.STRUCTURE);
+            return new ArrayList<>(NativeStructureGenerationKeys.reachable(level, possibleBiomes));
-            for (Map.Entry<ResourceKey<Structure>, Structure> entry : registry.entrySet()) {
-                if (hasPossibleBiome(entry.getValue(), possibleBiomes)) {
-                    keys.add(entry.getKey().identifier().toString());
-                }
-            }
         } catch (RuntimeException error) {
             throw new IllegalStateException("Iris failed to resolve reachable structures for modded level '"
                     + level.dimension().identifier() + "'", error);
         }
-        return keys;
     }
 
     @Override
@@ -401,16 +395,6 @@ public final class ModdedStructureHooks implements PlatformStructureHooks {
         return keys;
     }
 
-    private static boolean hasPossibleBiome(Structure structure, Set<String> possibleBiomeKeys) {
-        for (Holder<Biome> holder : structure.biomes()) {
-            Optional<ResourceKey<Biome>> key = holder.unwrapKey();
-            if (key.isPresent() && possibleBiomeKeys.contains(key.get().identifier().toString())) {
-                return true;
-            }
-        }
-        return false;
-    }
-
     private static ServerLevel level(PlatformWorld world) {
         return world instanceof ModdedPlatformWorld moddedWorld ? moddedWorld.level() : null;
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedCommandHelp.java

@@ -54,6 +54,9 @@ import static art.arcane.iris.modded.command.ModdedCommandFeedback.USAGE_ICON;
 final class ModdedCommandHelp {
     private static final int PAGE_SIZE = 17;
     private static final int PAGE_BUTTON_WIDTH = 10;
+    private static final TextKey COMMAND_UNREGISTERED = TextKey.of(
+            "iris.modded.help.entry.command.unregistered",
+            "Print every structure excluded from goto completion and its exact reason to the server console");
     private static final Map<String, List<Entry>> SECTIONS = new LinkedHashMap<>();
 
     static {
@@ -98,6 +101,7 @@ final class ModdedCommandHelp {
                 Entry.command("biome", "<key>", ModdedHelpMessages.COMMAND_BIOME_FIND_AN_IRIS_BIOME),
                 Entry.command("region", "<key>", ModdedHelpMessages.COMMAND_REGION_FIND_AN_IRIS_REGION),
                 Entry.command("object", "<key>", ModdedHelpMessages.COMMAND_OBJECT_FIND_AN_OBJECT_PLACEMENT),
+                Entry.command("unregistered", "", COMMAND_UNREGISTERED),
                 Entry.command("structure", "<key>", ModdedHelpMessages.COMMAND_STRUCTURE_FIND_AN_IRIS_PLACED_OR_NATIVE_DATAPACK_STRUCTURE),
                 Entry.command("poi", "<type>", ModdedHelpMessages.COMMAND_POI_FIND_A_SUPPORTED_POINT_OF_INTEREST)
         ));

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedCommandSuggestions.java

@@ -21,6 +21,10 @@ package art.arcane.iris.modded.command;
 import art.arcane.iris.core.pack.PackDirectoryResolver;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.framework.IrisStructureLocator;
+import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
+import art.arcane.iris.engine.framework.StructureReachability;
+import art.arcane.iris.engine.object.IrisNativeStructureDecision;
+import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
 import art.arcane.iris.modded.IrisModdedChunkGenerator;
 import art.arcane.iris.modded.ModdedEngineBootstrap;
 import art.arcane.iris.modded.ModdedServerLevels;
@@ -41,11 +45,16 @@ import org.slf4j.LoggerFactory;
 import java.io.File;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
+import java.util.Map;
 import java.util.Set;
+import java.util.TreeMap;
 import java.util.TreeSet;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Predicate;
 
 final class ModdedCommandSuggestions {
     static final SuggestionProvider<CommandSourceStack> BIOME_KEYS = (CommandContext<CommandSourceStack> context, SuggestionsBuilder builder) -> suggestBiomeKeys(context, builder);
@@ -103,22 +112,62 @@ final class ModdedCommandSuggestions {
     }
 
     static CompletableFuture<Suggestions> suggestStructureKeys(CommandContext<CommandSourceStack> context, SuggestionsBuilder builder) {
-        ModdedCommandFeedback.tab(context.getSource());
+        CommandSourceStack source = context.getSource();
+        ModdedCommandFeedback.tab(source);
         try {
-            Engine engine = IrisModdedCommands.engineFor(context.getSource().getLevel());
+            ServerLevel level = source.getLevel();
-            Collection<String> irisKeys = engine == null ? List.of() : IrisStructureLocator.placedKeys(engine);
+            Engine engine = IrisModdedCommands.engineFor(level);
-            Registry<Structure> registry = context.getSource().getServer().registryAccess().lookupOrThrow(Registries.STRUCTURE);
+            if (engine == null) {
-            List<String> nativeKeys = new ArrayList<>(registry.keySet().size());
+                return builder.buildFuture();
-            for (Identifier identifier : registry.keySet()) {
-                nativeKeys.add(identifier.toString());
             }
-            return SharedSuggestionProvider.suggest(combineStructureKeys(irisKeys, nativeKeys), builder);
+            boolean nativeGenerationEnabled =
+                    source.getServer().getWorldGenSettings().options().generateStructures();
+            Collection<String> irisKeys = IrisStructureLocator.locatableEditableKeys(engine);
+            Set<String> reachableNativeKeys = StructureReachability.reachableKeys(engine);
+            Registry<Structure> registry = source.getServer().registryAccess().lookupOrThrow(Registries.STRUCTURE);
+            List<String> nativeKeys = new ArrayList<>(registry.keySet().size());
+            Set<String> registeredKeys = new HashSet<>(registry.keySet().size());
+            for (Identifier identifier : registry.keySet()) {
+                String key = identifier.toString();
+                registeredKeys.add(normalizeKey(key));
+                IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(engine, key, false);
+                boolean nativePlacement = IrisStructureLocator.hasNativePlacement(engine, key);
+                boolean locatableNativePlacement = nativePlacement
+                        && IrisStructureLocator.hasLocatableNativePlacement(engine, key);
+                boolean locatableEditableReplacement = !nativePlacement
+                        && decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS
+                        && IrisStructureLocator.hasLocatableEditablePlacement(engine, key);
+                if (isEligibleRegisteredStructure(decision, nativePlacement,
+                        locatableNativePlacement, locatableEditableReplacement,
+                        reachableNativeKeys.contains(normalizeKey(key)), nativeGenerationEnabled)) {
+                    nativeKeys.add(key);
+                }
+            }
+            Collection<String> unregisteredIrisKeys = eligibleUnregisteredEditableKeys(
+                    irisKeys, registeredKeys,
+                    (String candidate) -> IrisStructureLocator.hasNativePlacement(engine, candidate));
+            return SharedSuggestionProvider.suggest(
+                    combineStructureKeys(unregisteredIrisKeys, nativeKeys), builder);
         } catch (Throwable e) {
-            warnTabFailure("structure keys", context.getSource(), e);
+            warnTabFailure("structure keys", source, e);
         }
         return builder.buildFuture();
     }
 
+    static boolean isEligibleRegisteredStructure(IrisNativeStructureDecision decision,
+                                                 boolean nativePlacement,
+                                                 boolean locatableNativePlacement,
+                                                 boolean locatableEditableReplacement,
+                                                 boolean reachable,
+                                                 boolean nativeGenerationEnabled) {
+        if (decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+            return locatableEditableReplacement
+                    || nativeGenerationEnabled && nativePlacement && locatableNativePlacement;
+        }
+        return nativeGenerationEnabled && decision.generate()
+                && (reachable || nativePlacement && locatableNativePlacement);
+    }
+
     static void warnTabFailure(String suggestion, CommandSourceStack source, Throwable error) {
         String origin = tabOrigin(source);
         if (!REPORTED_TAB_FAILURES.add(suggestion + '|' + origin + '|' + error.getClass().getName())) {
@@ -142,10 +191,38 @@ final class ModdedCommandSuggestions {
     }
 
     static List<String> combineStructureKeys(Collection<String> irisKeys, Collection<String> nativeKeys) {
-        Set<String> combined = new TreeSet<>();
+        Map<String, String> combined = new TreeMap<>();
-        combined.addAll(irisKeys);
+        addStructureKeys(combined, irisKeys);
-        combined.addAll(nativeKeys);
+        addStructureKeys(combined, nativeKeys);
-        return List.copyOf(combined);
+        return List.copyOf(combined.values());
+    }
+
+    static List<String> eligibleUnregisteredEditableKeys(
+            Collection<String> irisKeys, Set<String> normalizedRegisteredKeys,
+            Predicate<String> nativePlacement) {
+        List<String> filtered = new ArrayList<>(irisKeys.size());
+        for (String key : irisKeys) {
+            String normalizedKey = normalizeKey(key);
+            if (!normalizedKey.isEmpty()
+                    && !normalizedRegisteredKeys.contains(normalizedKey)
+                    && !nativePlacement.test(key)) {
+                filtered.add(key.trim());
+            }
+        }
+        return List.copyOf(filtered);
+    }
+
+    private static void addStructureKeys(Map<String, String> combined, Collection<String> keys) {
+        for (String key : keys) {
+            String normalizedKey = normalizeKey(key);
+            if (!normalizedKey.isEmpty()) {
+                combined.putIfAbsent(normalizedKey, key.trim());
+            }
+        }
+    }
+
+    static String normalizeKey(String key) {
+        return key == null ? "" : key.trim().toLowerCase(Locale.ROOT);
     }
 
     private static CompletableFuture<Suggestions> suggestPackNames(CommandContext<CommandSourceStack> context, SuggestionsBuilder builder) {

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedCommandTree.java

@@ -242,6 +242,9 @@ final class ModdedCommandTree {
                 .then(Commands.literal("object")
                         .then(Commands.argument("key", StringArgumentType.greedyString()).suggests(ModdedCommandSuggestions.OBJECT_KEYS)
                                 .executes((CommandContext<CommandSourceStack> context) -> ModdedLocateCommands.gotoObject(context.getSource(), StringArgumentType.getString(context, "key")))))
+                .then(Commands.literal("unregistered")
+                        .executes((CommandContext<CommandSourceStack> context) ->
+                                ModdedUnregisteredStructures.print(context.getSource())))
                 .then(Commands.literal("structure")
                         .then(Commands.argument("key", StringArgumentType.greedyString()).suggests(ModdedCommandSuggestions.STRUCTURE_KEYS)
                                 .executes((CommandContext<CommandSourceStack> context) -> ModdedLocateCommands.gotoStructure(context.getSource(), StringArgumentType.getString(context, "key")))))

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedLocateCommands.java

@@ -26,6 +26,7 @@ import art.arcane.iris.engine.framework.GenerationSessionLease;
 import art.arcane.iris.engine.framework.IrisStructureLocator;
 import art.arcane.iris.engine.framework.Locator;
 import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
+import art.arcane.iris.engine.framework.StructureReachability;
 import art.arcane.iris.engine.framework.WrongEngineBroException;
 import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisNativeStructureDecision;
@@ -157,7 +158,8 @@ final class ModdedLocateCommands {
         }
         Optional<NativeStructureTarget> resolved = resolveNativeStructure(source, level, engine, key);
         if (resolved.isEmpty()) {
-            if (IrisStructureLocator.isPlaced(engine, key)) {
+            if (!IrisStructureLocator.hasNativePlacement(engine, key)
+                    && IrisStructureLocator.hasLocatableEditablePlacement(engine, key)) {
                 locateIrisStructure(source, level, engine, player, key);
                 return 1;
             }
@@ -166,31 +168,74 @@ final class ModdedLocateCommands {
         }
         NativeStructureTarget target = resolved.get();
         IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(engine, target.key(), false);
-        if (!decision.generate()
+        boolean nativeGenerationEnabled =
-                && decision.status() != NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+                source.getServer().getWorldGenSettings().options().generateStructures();
-            IrisModdedCommands.fail(source, NativeStructureGenerationPolicy.generationStatusMessage(
+        boolean nativePlacement = IrisStructureLocator.hasNativePlacement(engine, target.key());
-                    target.key(), decision.status()));
+        boolean locatableNativePlacement = nativePlacement
+                && IrisStructureLocator.hasLocatableNativePlacement(engine, target.key());
+        boolean locatableEditableReplacement = !nativePlacement
+                && decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS
+                && IrisStructureLocator.hasLocatableEditablePlacement(engine, target.key());
+        boolean reachable = StructureReachability.isReachable(engine, target.key());
+        if (!ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                decision, nativePlacement, locatableNativePlacement, locatableEditableReplacement,
+                reachable, nativeGenerationEnabled)) {
+            IrisModdedCommands.fail(source, registeredStructureUnavailableMessage(
+                    target.key(), target.availability(), decision,
+                    nativePlacement, locatableNativePlacement,
+                    nativeGenerationEnabled, reachable));
             return 0;
         }
-        if (decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+        if (locatableEditableReplacement) {
-            if (!IrisStructureLocator.hasNativePlacement(engine, target.key())) {
+            locateIrisStructure(source, level, engine, player, target.key());
-                locateIrisStructure(source, level, engine, player, target.key());
-                return 1;
-            }
-            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_SEARCHING_NATIVE_STRUCTURE_WITHIN_CHUNKS, MessageArgument.untrusted("value", target.key()), MessageArgument.untrusted("NATIVESTRUCTURELOCATERADIUS", NATIVE_STRUCTURE_LOCATE_RADIUS)));
-            runNativeStructureLocate(source, level, player, target);
             return 1;
         }
-        if (!IrisStructureLocator.hasNativePlacement(engine, target.key())
-                && target.availability() != NativeStructureAvailability.AVAILABLE) {
-            IrisModdedCommands.fail(source, nativeUnavailableMessage(target.key(), target.availability()));
-            return 0;
-        }
         IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_SEARCHING_NATIVE_STRUCTURE_WITHIN_CHUNKS, MessageArgument.untrusted("value", target.key()), MessageArgument.untrusted("NATIVESTRUCTURELOCATERADIUS", NATIVE_STRUCTURE_LOCATE_RADIUS)));
         runNativeStructureLocate(source, level, player, target);
         return 1;
     }
 
+    static String registeredStructureUnavailableMessage(
+            String key, NativeStructureAvailability nativeAvailability,
+            IrisNativeStructureDecision decision,
+            boolean nativePlacement, boolean locatableNativePlacement,
+            boolean nativeGenerationEnabled, boolean reachable) {
+        if (!decision.generate()
+                && decision.status() != NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+            return NativeStructureGenerationPolicy.generationStatusMessage(key, decision.status());
+        }
+        if (decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+            if (nativePlacement && !nativeGenerationEnabled) {
+                return withInactiveNativePlacement(
+                        nativeUnavailableMessage(key, NativeStructureAvailability.WORLD_DISABLED),
+                        nativePlacement, locatableNativePlacement);
+            }
+            return "Iris replacement " + key
+                    + " is configured, but every matching placement has non-positive density or a Y band "
+                    + "outside this world's height range.";
+        }
+        if (!nativeGenerationEnabled) {
+            return withInactiveNativePlacement(
+                    nativeUnavailableMessage(key, NativeStructureAvailability.WORLD_DISABLED),
+                    nativePlacement, locatableNativePlacement);
+        }
+        NativeStructureAvailability availability = nativeAvailability;
+        if (availability == NativeStructureAvailability.AVAILABLE && !reachable) {
+            availability = NativeStructureAvailability.NO_PLACEMENT;
+        }
+        return withInactiveNativePlacement(
+                nativeUnavailableMessage(key, availability), nativePlacement, locatableNativePlacement);
+    }
+
+    private static String withInactiveNativePlacement(
+            String reason, boolean nativePlacement, boolean locatableNativePlacement) {
+        if (!nativePlacement || locatableNativePlacement) {
+            return reason;
+        }
+        return reason + " A matching Iris nativeStructures placement is also configured, but has non-positive "
+                + "density or a Y band outside this world's height range.";
+    }
+
     private static void locateIrisStructure(CommandSourceStack source, ServerLevel level, Engine engine,
                                             ServerPlayer player, String key) {
         MinecraftServer server = source.getServer();
@@ -311,7 +356,7 @@ final class ModdedLocateCommands {
                 case AVAILABLE -> available++;
                 case WORLD_DISABLED, FILTERED -> disabled++;
                 case IRIS_SUPPRESSED -> suppressed++;
-                case BIOME_UNREACHABLE -> unreachableBiomes++;
+                case EMPTY_BIOME_FILTER, BIOME_UNREACHABLE -> unreachableBiomes++;
                 case NO_PLACEMENT -> unsupported++;
             }
         }
@@ -361,25 +406,28 @@ final class ModdedLocateCommands {
         return Optional.of(new NativeStructureTarget(key, holder.get(), availability));
     }
 
-    private static NativeStructureAvailability nativeAvailability(CommandSourceStack source, ServerLevel level,
+    static NativeStructureAvailability nativeAvailability(CommandSourceStack source, ServerLevel level,
-                                                                   Engine engine, String key,
+                                                           Engine engine, String key,
-                                                                   Holder.Reference<Structure> holder) {
+                                                           Holder.Reference<Structure> holder) {
         boolean worldEnabled = source.getServer().getWorldGenSettings().options().generateStructures();
         IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(engine, key, false);
         boolean selected = decision.status() != NativeStructureGenerationStatus.DISABLED_BY_PACK;
         boolean suppressed = decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS;
+        boolean biomeFilterEmpty = holder.value().biomes().stream().findAny().isEmpty();
         ChunkGenerator chunkGenerator = level.getChunkSource().getGenerator();
         boolean biomeReachable = chunkGenerator instanceof IrisModdedChunkGenerator irisGenerator
                 && irisGenerator.isNativeStructureReachable(holder);
         boolean hasPlacement = false;
-        if (worldEnabled && selected && !suppressed && biomeReachable) {
+        if (worldEnabled && selected && !suppressed && !biomeFilterEmpty && biomeReachable) {
             hasPlacement = !level.getChunkSource().getGeneratorState().getPlacementsForStructure(holder).isEmpty();
         }
-        return classifyNativeAvailability(worldEnabled, selected, suppressed, biomeReachable, hasPlacement);
+        return classifyNativeAvailability(
+                worldEnabled, selected, suppressed, biomeFilterEmpty, biomeReachable, hasPlacement);
     }
 
     static NativeStructureAvailability classifyNativeAvailability(boolean worldEnabled, boolean selected,
-                                                                   boolean suppressed, boolean biomeReachable,
+                                                                   boolean suppressed, boolean biomeFilterEmpty,
+                                                                   boolean biomeReachable,
                                                                    boolean hasPlacement) {
         if (!worldEnabled) {
             return NativeStructureAvailability.WORLD_DISABLED;
@@ -390,6 +438,9 @@ final class ModdedLocateCommands {
         if (suppressed) {
             return NativeStructureAvailability.IRIS_SUPPRESSED;
         }
+        if (biomeFilterEmpty) {
+            return NativeStructureAvailability.EMPTY_BIOME_FILTER;
+        }
         if (!biomeReachable) {
             return NativeStructureAvailability.BIOME_UNREACHABLE;
         }
@@ -399,15 +450,19 @@ final class ModdedLocateCommands {
         return NativeStructureAvailability.AVAILABLE;
     }
 
-    private static String nativeUnavailableMessage(String key, NativeStructureAvailability availability) {
+    static String nativeUnavailableMessage(String key, NativeStructureAvailability availability) {
         return switch (availability) {
             case WORLD_DISABLED -> "Native structure generation is disabled for this world, so " + key + " cannot generate or be located.";
             case FILTERED -> NativeStructureGenerationPolicy.generationStatusMessage(
                     key, NativeStructureGenerationStatus.DISABLED_BY_PACK);
             case IRIS_SUPPRESSED -> NativeStructureGenerationPolicy.generationStatusMessage(
                     key, NativeStructureGenerationStatus.REPLACED_BY_IRIS);
+            case EMPTY_BIOME_FILTER -> "Native structure " + key
+                    + " has a biome tag or filter that resolves to zero registered biomes.";
             case BIOME_UNREACHABLE -> "Native structure " + key + " cannot generate because none of its required biomes are produced by this Iris pack.";
-            case NO_PLACEMENT -> "Native structure " + key + " is registered, but its structure set has no placement supported by this dimension's generator state.";
+            case NO_PLACEMENT -> "Native structure " + key
+                    + " is registered and biome-compatible, but has no active positive-weight, "
+                    + "positive-frequency structure-set placement in this dimension's generator state.";
             case AVAILABLE -> "Native structure " + key + " is available.";
         };
     }
@@ -531,6 +586,7 @@ final class ModdedLocateCommands {
         WORLD_DISABLED,
         FILTERED,
         IRIS_SUPPRESSED,
+        EMPTY_BIOME_FILTER,
         BIOME_UNREACHABLE,
         NO_PLACEMENT
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedUnregisteredStructures.java

@@ -0,0 +1,204 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.framework.IrisStructureLocator;
+import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
+import art.arcane.iris.engine.framework.StructureReachability;
+import art.arcane.iris.engine.object.IrisNativeStructureDecision;
+import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
+import net.minecraft.commands.CommandSourceStack;
+import net.minecraft.core.Holder;
+import net.minecraft.core.Registry;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.Identifier;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.levelgen.structure.Structure;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.function.Predicate;
+
+final class ModdedUnregisteredStructures {
+    private static final Logger LOGGER = LoggerFactory.getLogger("Iris");
+
+    private ModdedUnregisteredStructures() {
+    }
+
+    static int print(CommandSourceStack source) {
+        ServerLevel level = source.getLevel();
+        Engine engine = IrisModdedCommands.engineFor(level);
+        if (engine == null) {
+            IrisModdedCommands.fail(source,
+                    "This dimension is not generated by Iris, so it has no Iris structure eligibility report.");
+            return 0;
+        }
+        try {
+            List<ExcludedStructure> excluded = collect(source, level, engine);
+            String dimension = level.dimension().identifier().toString();
+            long unregistered = excluded.stream()
+                    .filter((ExcludedStructure entry) -> entry.status() == ReportStatus.UNREGISTERED)
+                    .count();
+            long unplaced = excluded.stream()
+                    .filter((ExcludedStructure entry) -> entry.status() == ReportStatus.UNPLACED)
+                    .count();
+            long hidden = excluded.size() - unregistered - unplaced;
+            LOGGER.info("[Iris goto unregistered] {} structure candidate(s) excluded from /iris goto structure in {}",
+                    excluded.size(), dimension);
+            for (ExcludedStructure entry : excluded) {
+                LOGGER.info("[Iris goto unregistered] [{}] {} - {}",
+                        entry.status().label(), entry.key(), entry.reason());
+            }
+            LOGGER.info("[Iris goto unregistered] Inventory scope is the live registry, this pack's "
+                    + "nativeStructures placements, and structureLoader editable resources. This is deterministic "
+                    + "eligibility analysis and performs no chunk search; absent unmanaged datapack resources "
+                    + "cannot be inferred after registry loading.");
+            IrisModdedCommands.ok(source, "Iris wrote " + excluded.size() + " structure candidate(s) for "
+                    + dimension + " to the server console (" + hidden + " excluded, "
+                    + unregistered + " unregistered, " + unplaced + " unplaced).");
+            return 1;
+        } catch (Throwable error) {
+            LOGGER.error("Iris failed to build the excluded structure report for {}",
+                    level.dimension().identifier(), error);
+            IrisModdedCommands.fail(source,
+                    "Iris could not build the excluded structure report; see the server console.");
+            return 0;
+        }
+    }
+
+    static List<ExcludedStructure> collect(CommandSourceStack source, ServerLevel level, Engine engine) {
+        boolean nativeGenerationEnabled =
+                source.getServer().getWorldGenSettings().options().generateStructures();
+        Set<String> reachableNativeKeys = StructureReachability.reachableKeys(engine);
+        Registry<Structure> registry = source.getServer().registryAccess().lookupOrThrow(Registries.STRUCTURE);
+        Map<String, ExcludedStructure> excluded = new TreeMap<>();
+        Set<String> registeredKeys = new HashSet<>(registry.keySet().size());
+        Set<String> eligibleRegisteredKeys = new HashSet<>(registry.keySet().size());
+        for (Identifier identifier : registry.keySet()) {
+            String key = identifier.toString();
+            String normalizedKey = ModdedCommandSuggestions.normalizeKey(key);
+            registeredKeys.add(normalizedKey);
+            Optional<Holder.Reference<Structure>> holder = registry.get(identifier);
+            if (holder.isEmpty()) {
+                excluded.put(normalizedKey, new ExcludedStructure(ReportStatus.EXCLUDED,
+                        key, "The live structure registry contains this key but has no bound structure holder."));
+                continue;
+            }
+            IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(engine, key, false);
+            boolean nativePlacement = IrisStructureLocator.hasNativePlacement(engine, key);
+            boolean locatableNativePlacement = nativePlacement
+                    && IrisStructureLocator.hasLocatableNativePlacement(engine, key);
+            boolean locatableEditableReplacement = !nativePlacement
+                    && decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS
+                    && IrisStructureLocator.hasLocatableEditablePlacement(engine, key);
+            boolean reachable = reachableNativeKeys.contains(normalizedKey);
+            if (ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                    decision, nativePlacement, locatableNativePlacement,
+                    locatableEditableReplacement, reachable, nativeGenerationEnabled)) {
+                eligibleRegisteredKeys.add(normalizedKey);
+                continue;
+            }
+            ModdedLocateCommands.NativeStructureAvailability availability =
+                    ModdedLocateCommands.nativeAvailability(source, level, engine, key, holder.get());
+            String reason = ModdedLocateCommands.registeredStructureUnavailableMessage(
+                    key, availability, decision, nativePlacement, locatableNativePlacement,
+                    nativeGenerationEnabled, reachable);
+            excluded.put(normalizedKey, new ExcludedStructure(ReportStatus.EXCLUDED, key, reason));
+        }
+        List<String> absentNativeKeys = missingConfiguredNativeKeys(
+                IrisStructureLocator.placedKeys(engine), registeredKeys,
+                (String key) -> IrisStructureLocator.hasNativePlacement(engine, key));
+        for (String key : absentNativeKeys) {
+            String normalizedKey = ModdedCommandSuggestions.normalizeKey(key);
+            excluded.putIfAbsent(normalizedKey, new ExcludedStructure(ReportStatus.UNREGISTERED, key,
+                    "Configured by an Iris nativeStructures placement, but absent from the live structure registry; "
+                            + "install or enable the datapack or mod that provides this key."));
+        }
+        if (engine.getData().getStructureLoader() != null) {
+            for (String key : engine.getData().getStructureLoader().getPossibleKeys()) {
+                String normalizedKey = ModdedCommandSuggestions.normalizeKey(key);
+                if (normalizedKey.isEmpty() || eligibleRegisteredKeys.contains(normalizedKey)
+                        || excluded.containsKey(normalizedKey)) {
+                    continue;
+                }
+                boolean registered = registeredKeys.contains(normalizedKey);
+                boolean nativePlacement = IrisStructureLocator.hasNativePlacement(engine, key);
+                boolean locatableEditable = IrisStructureLocator.hasLocatableEditablePlacement(engine, key);
+                if (!registered && !nativePlacement && locatableEditable) {
+                    continue;
+                }
+                boolean configured = IrisStructureLocator.hasEditablePlacement(engine, key);
+                excluded.putIfAbsent(normalizedKey, new ExcludedStructure(
+                        ReportStatus.UNPLACED, key.trim(), editableExclusionReason(configured)));
+            }
+        }
+        return List.copyOf(excluded.values());
+    }
+
+    static List<String> missingConfiguredNativeKeys(
+            Collection<String> placedKeys, Set<String> normalizedRegisteredKeys,
+            Predicate<String> nativePlacement) {
+        Map<String, String> missing = new TreeMap<>();
+        for (String key : placedKeys) {
+            String normalizedKey = ModdedCommandSuggestions.normalizeKey(key);
+            if (!normalizedKey.isEmpty()
+                    && !normalizedRegisteredKeys.contains(normalizedKey)
+                    && nativePlacement.test(key)) {
+                missing.putIfAbsent(normalizedKey, key.trim());
+            }
+        }
+        return List.copyOf(missing.values());
+    }
+
+    static String editableExclusionReason(boolean configured) {
+        if (!configured) {
+            return "Editable Iris structure resource is loaded, but no biome, region, or dimension structure "
+                    + "placement references it.";
+        }
+        return "Editable Iris structure resource is referenced by a placement, but every matching placement "
+                + "has non-positive density or a Y band outside this world's height range.";
+    }
+
+    enum ReportStatus {
+        EXCLUDED("excluded"),
+        UNREGISTERED("unregistered"),
+        UNPLACED("unplaced");
+
+        private final String label;
+
+        ReportStatus(String label) {
+            this.label = label;
+        }
+
+        String label() {
+            return label;
+        }
+    }
+
+    record ExcludedStructure(ReportStatus status, String key, String reason) {
+    }
+}

adapters/modded-common/src/test/java/art/arcane/iris/modded/command/IrisModdedCommandParityTest.java

@@ -39,6 +39,7 @@ public class IrisModdedCommandParityTest {
         child(iris, "height");
         child(iris, "worlds");
         child(iris, "accesslist");
+        child(child(iris, "goto"), "unregistered");
 
         CommandNode<CommandSourceStack> edit = child(iris, "edit");
         child(edit, "b");
@@ -75,6 +76,7 @@ public class IrisModdedCommandParityTest {
         assertTrue(ModdedCommandHelp.documents("studio", "pkg"));
         assertTrue(ModdedCommandHelp.documents("object", "we"));
         assertTrue(ModdedCommandHelp.documents("world", "mainworld"));
+        assertTrue(ModdedCommandHelp.documents("goto", "unregistered"));
     }
 
     @Test

adapters/modded-common/src/test/java/art/arcane/iris/modded/command/IrisModdedStructureCommandTest.java

@@ -1,5 +1,7 @@
 package art.arcane.iris.modded.command;
 
+import art.arcane.iris.engine.object.IrisNativeStructureDecision;
+import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
 import art.arcane.iris.nativegen.NativeStructureLocateResults;
 import com.mojang.datafixers.util.Pair;
 import net.minecraft.core.BlockPos;
@@ -8,6 +10,8 @@ import org.junit.Test;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.List;
+import java.util.Set;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.junit.Assert.assertEquals;
@@ -49,7 +53,7 @@ public class IrisModdedStructureCommandTest {
         String source = source("ModdedLocateCommands.java");
         String suggestions = source("ModdedCommandSuggestions.java");
 
-        assertTrue(source.contains("IrisStructureLocator.isPlaced(engine, key)"));
+        assertTrue(source.contains("IrisStructureLocator.hasLocatableEditablePlacement(engine, key)"));
         assertTrue(source.contains("registry.get(identifier)"));
         assertTrue(source.contains("getPlacementsForStructure(holder)"));
         assertTrue(source.contains("generator.findNearestMapStructure("));
@@ -57,7 +61,7 @@ public class IrisModdedStructureCommandTest {
         assertTrue(source.contains("HolderSet.direct(target.holder())"));
         assertFalse(source.contains("NativeStructureLocateCapability"));
         assertTrue(source.contains("boolean teleported = player.teleportTo("));
-        assertTrue(suggestions.contains("combineStructureKeys(irisKeys, nativeKeys)"));
+        assertTrue(suggestions.contains("combineStructureKeys(unregisteredIrisKeys, nativeKeys)"));
         assertTrue(source.contains("irisGenerator.isNativeStructureReachable(holder)"));
         assertTrue(source.contains("LocateStatus.SEARCH_LIMIT_REACHED"));
         assertTrue(source.contains("IRIS_MODDED_COMMANDS_UNABLE_LOCATE_IRIS_PLACED_STRUCTURE_DENSITY_SEARCH_SAFETY_LIMIT_WAS"));
@@ -68,6 +72,148 @@ public class IrisModdedStructureCommandTest {
         assertFalse(source.contains("at[2] + 8"));
     }
 
+    @Test
+    public void registeredStructureEligibilityMatchesGotoAndSuggestions() {
+        IrisNativeStructureDecision nativeDecision = decision(NativeStructureGenerationStatus.GENERATE_NATIVE);
+        IrisNativeStructureDecision replacementDecision = decision(
+                NativeStructureGenerationStatus.REPLACED_BY_IRIS);
+        IrisNativeStructureDecision disabledDecision = decision(
+                NativeStructureGenerationStatus.DISABLED_BY_PACK);
+
+        assertTrue(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                nativeDecision, false, false, false, true, true));
+        assertTrue(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                nativeDecision, true, true, false, false, true));
+        assertFalse(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                nativeDecision, true, false, false, false, true));
+        assertFalse(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                nativeDecision, true, true, false, true, false));
+        assertTrue(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                replacementDecision, false, false, true, false, false));
+        assertTrue(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                replacementDecision, true, true, false, false, true));
+        assertFalse(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                replacementDecision, true, true, false, false, false));
+        assertFalse(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                replacementDecision, false, false, false, true, true));
+        assertFalse(ModdedCommandSuggestions.isEligibleRegisteredStructure(
+                disabledDecision, true, true, true, true, true));
+    }
+
+    @Test
+    public void structureSuggestionsDedupeAndSortPlacedAndNativeKeys() {
+        List<String> suggestions = ModdedCommandSuggestions.combineStructureKeys(
+                List.of("towns_and_towers:village_forest", "minecraft:village_plains",
+                        "towns_and_towers:village_forest", "MINECRAFT:VILLAGE_PLAINS"),
+                List.of("minecraft:stronghold", "minecraft:village_plains"));
+
+        assertEquals(List.of("minecraft:stronghold", "minecraft:village_plains",
+                "towns_and_towers:village_forest"), suggestions);
+    }
+
+    @Test
+    public void structureSuggestionsCannotReintroduceRegistryOrNativePlacementCollisions() {
+        List<String> suggestions = ModdedCommandSuggestions.eligibleUnregisteredEditableKeys(
+                List.of("iris:custom", "minecraft:disabled", "MINECRAFT:UNREACHABLE",
+                        "iris:native_collision"),
+                Set.of("minecraft:disabled", "minecraft:unreachable"),
+                (String key) -> key.equalsIgnoreCase("iris:native_collision"));
+
+        assertEquals(List.of("iris:custom"), suggestions);
+    }
+
+    @Test
+    public void unregisteredReportFindsOnlyConfiguredNativeKeysAbsentFromRegistry() {
+        List<String> missing = ModdedUnregisteredStructures.missingConfiguredNativeKeys(
+                List.of("iris:editable", "missing:native", "MISSING:NATIVE", "registered:native"),
+                Set.of("registered:native"),
+                (String key) -> key.equalsIgnoreCase("missing:native")
+                        || key.equalsIgnoreCase("registered:native"));
+
+        assertEquals(List.of("missing:native"), missing);
+    }
+
+    @Test
+    public void unregisteredReportDistinguishesEveryNativeExclusionReason() {
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.WORLD_DISABLED,
+                ModdedLocateCommands.classifyNativeAvailability(false, true, false, false, true, true));
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.FILTERED,
+                ModdedLocateCommands.classifyNativeAvailability(true, false, false, false, true, true));
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.IRIS_SUPPRESSED,
+                ModdedLocateCommands.classifyNativeAvailability(true, true, true, false, true, true));
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.EMPTY_BIOME_FILTER,
+                ModdedLocateCommands.classifyNativeAvailability(true, true, false, true, false, false));
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.BIOME_UNREACHABLE,
+                ModdedLocateCommands.classifyNativeAvailability(true, true, false, false, false, false));
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.NO_PLACEMENT,
+                ModdedLocateCommands.classifyNativeAvailability(true, true, false, false, true, false));
+        assertEquals(ModdedLocateCommands.NativeStructureAvailability.AVAILABLE,
+                ModdedLocateCommands.classifyNativeAvailability(true, true, false, false, true, true));
+
+        assertTrue(ModdedLocateCommands.nativeUnavailableMessage(
+                "towns_and_towers:exclusive",
+                ModdedLocateCommands.NativeStructureAvailability.EMPTY_BIOME_FILTER)
+                .contains("resolves to zero registered biomes"));
+        assertTrue(ModdedLocateCommands.nativeUnavailableMessage(
+                "minecraft:village_plains",
+                ModdedLocateCommands.NativeStructureAvailability.NO_PLACEMENT)
+                .contains("no active positive-weight, positive-frequency structure-set placement"));
+        String combined = ModdedLocateCommands.registeredStructureUnavailableMessage(
+                "towns_and_towers:exclusive",
+                ModdedLocateCommands.NativeStructureAvailability.EMPTY_BIOME_FILTER,
+                decision(NativeStructureGenerationStatus.GENERATE_NATIVE),
+                true, false, true, false);
+        assertTrue(combined.contains("resolves to zero registered biomes"));
+        assertTrue(combined.contains("matching Iris nativeStructures placement is also configured"));
+    }
+
+    @Test
+    public void unregisteredReportExplainsEditablePlacementState() {
+        assertTrue(ModdedUnregisteredStructures.editableExclusionReason(false)
+                .contains("no biome, region, or dimension structure placement"));
+        assertTrue(ModdedUnregisteredStructures.editableExclusionReason(true)
+                .contains("non-positive density or a Y band outside"));
+    }
+
+    @Test
+    public void unregisteredCommandUsesGotoEligibilityAndPrintsToConsole() throws IOException {
+        String command = source("ModdedUnregisteredStructures.java");
+        String tree = source("ModdedCommandTree.java");
+
+        assertTrue(tree.contains("Commands.literal(\"unregistered\")"));
+        assertTrue(tree.contains("ModdedUnregisteredStructures.print(context.getSource())"));
+        assertTrue(command.contains("ModdedCommandSuggestions.isEligibleRegisteredStructure("));
+        assertTrue(command.contains("ModdedLocateCommands.registeredStructureUnavailableMessage("));
+        assertTrue(command.contains("engine.getData().getStructureLoader().getPossibleKeys()"));
+        assertTrue(command.contains("IrisStructureLocator.hasLocatableEditablePlacement(engine, key)"));
+        assertTrue(command.contains("LOGGER.info(\"[Iris goto unregistered] [{}] {} - {}\""));
+        assertTrue(command.contains("UNREGISTERED(\"unregistered\")"));
+        assertFalse(command.contains("DatapackIngestService"));
+    }
+
+    @Test
+    public void structureSuggestionsUseActiveLevelAvailability() throws IOException {
+        String suggestions = source("ModdedCommandSuggestions.java");
+        int methodStart = suggestions.indexOf("static CompletableFuture<Suggestions> suggestStructureKeys(");
+        int methodEnd = suggestions.indexOf("static boolean isEligibleRegisteredStructure(", methodStart);
+        String method = suggestions.substring(methodStart, methodEnd);
+
+        assertTrue(method.contains("ServerLevel level = source.getLevel()"));
+        assertTrue(method.contains("Engine engine = IrisModdedCommands.engineFor(level)"));
+        assertFalse(method.contains("IrisStructureLocator.locatableKeys(engine)"));
+        assertTrue(method.contains("IrisStructureLocator.locatableEditableKeys(engine)"));
+        assertTrue(method.contains("StructureReachability.reachableKeys(engine)"));
+        assertTrue(method.contains("NativeStructureGenerationPolicy.resolve(engine, key, false)"));
+        assertTrue(method.contains("IrisStructureLocator.hasLocatableNativePlacement(engine, key)"));
+        assertTrue(method.contains("IrisStructureLocator.hasLocatableEditablePlacement(engine, key)"));
+        assertTrue(method.contains("reachableNativeKeys.contains(normalizeKey(key))"));
+        assertTrue(method.contains("nativeGenerationEnabled"));
+        assertTrue(method.contains("eligibleUnregisteredEditableKeys("));
+        assertTrue(method.contains("IrisStructureLocator.hasNativePlacement(engine, candidate)"));
+        assertFalse(method.contains("NativeStructureGenerationKeys.active(level)"));
+        assertFalse(method.contains("getPlacementsForStructure"));
+    }
+
     @Test
     public void generatorLocateUsesEveryIrisPlacedNativeStructure() throws IOException {
         String source = moddedSource("ModdedNativeStructureStage.java");
@@ -111,20 +257,29 @@ public class IrisModdedStructureCommandTest {
         int methodEnd = source.indexOf("private static void locateIrisStructure(", methodStart);
         String method = source.substring(methodStart, methodEnd);
         int nativeResolution = method.indexOf("resolveNativeStructure(source, level, engine, key)");
-        int genericIrisLookup = method.indexOf("IrisStructureLocator.isPlaced(engine, key)", nativeResolution);
+        int editableIrisLookup = method.indexOf(
-        int policyResolution = method.indexOf("NativeStructureGenerationPolicy.resolve(engine, target.key(), false)", genericIrisLookup);
+                "IrisStructureLocator.hasLocatableEditablePlacement(engine, key)", nativeResolution);
-        int replacementCheck = method.indexOf(
+        int policyResolution = method.indexOf(
-                "decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS", policyResolution);
+                "NativeStructureGenerationPolicy.resolve(engine, target.key(), false)", editableIrisLookup);
-        int replacementLocate = method.indexOf("runNativeStructureLocate(source, level, player, target)",
+        int eligibilityCheck = method.indexOf(
-                replacementCheck);
+                "ModdedCommandSuggestions.isEligibleRegisteredStructure(", policyResolution);
+        int replacementLocate = method.indexOf(
+                "locateIrisStructure(source, level, engine, player, target.key())", eligibilityCheck);
+        int nativeLocate = method.indexOf("runNativeStructureLocate(source, level, player, target)",
+                replacementLocate);
 
         assertTrue(nativeResolution >= 0);
-        assertTrue(genericIrisLookup > nativeResolution);
+        assertTrue(editableIrisLookup > nativeResolution);
-        assertTrue(policyResolution > genericIrisLookup);
+        assertTrue(policyResolution > editableIrisLookup);
-        assertTrue(replacementCheck > policyResolution);
+        assertTrue(eligibilityCheck > policyResolution);
-        assertTrue(replacementLocate > replacementCheck);
+        assertTrue(replacementLocate > eligibilityCheck);
-        assertTrue(method.contains("!IrisStructureLocator.hasNativePlacement(engine, target.key())"));
+        assertTrue(nativeLocate > replacementLocate);
-        assertTrue(method.contains("&& target.availability() != NativeStructureAvailability.AVAILABLE"));
+        assertTrue(method.contains("IrisStructureLocator.hasLocatableNativePlacement(engine, target.key())"));
+        assertTrue(method.contains("IrisStructureLocator.hasLocatableEditablePlacement(engine, target.key())"));
+        assertTrue(method.contains("!IrisStructureLocator.hasNativePlacement(engine, key)"));
+        assertTrue(method.contains("StructureReachability.isReachable(engine, target.key())"));
+        assertTrue(method.contains("getWorldGenSettings().options().generateStructures()"));
+        assertFalse(method.contains("IrisStructureLocator.isPlaced(engine, key)"));
     }
 
     @Test
@@ -175,4 +330,8 @@ public class IrisModdedStructureCommandTest {
                 .resolve("../modded-common/src/main/java")
                 .normalize();
     }
+
+    private IrisNativeStructureDecision decision(NativeStructureGenerationStatus status) {
+        return new IrisNativeStructureDecision(status, 0, null, false, false, null, null);
+    }
 }

build.gradle

@@ -122,6 +122,8 @@ nmsBindings.each { key, value ->
                 rootProject.file('adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeStructurePostProcessor.java').absolutePath)
             systemProperty('iris.nativeStructureStartInjectorSource',
                 rootProject.file('adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeStructureStartInjector.java').absolutePath)
+            systemProperty('iris.nativeStructureGenerationKeysSource',
+                rootProject.file('adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeStructureGenerationKeys.java').absolutePath)
             systemProperty('iris.customBiomeSource',
                 rootProject.file("adapters/bukkit/nms/${key}/src/main/java/art/arcane/iris/core/nms/${key}/CustomBiomeSource.java").absolutePath)
             systemProperty('iris.vanillaStructureBiomesSource',

core/src/main/java/art/arcane/iris/engine/framework/IrisStructureLocator.java

@@ -69,9 +69,14 @@ public final class IrisStructureLocator {
     private static final Pattern NAMESPACED_RESOURCE_KEY = Pattern.compile("[a-z0-9_.-]+:[a-z0-9/._-]+");
 
     private static final Cache<Engine, PlacementIndex> INDEX_CACHE = Caffeine.newBuilder().weakKeys().build();
+    private static final Cache<Engine, LocatableIndex> LOCATABLE_INDEX_CACHE =
+            Caffeine.newBuilder().weakKeys().build();
     private static final PlacementIndex EMPTY_INDEX = new PlacementIndex(
             Collections.emptySet(), Collections.emptySet(), Collections.emptySet(), Collections.emptySet(),
             Collections.emptySet(), Collections.emptyList());
+    private static final LocatableIndex EMPTY_LOCATABLE_INDEX = new LocatableIndex(
+            Collections.emptySet(), Collections.emptySet(), Collections.emptySet(),
+            Collections.emptySet(), Collections.emptySet(), Collections.emptySet());
     private static final LocateResult NOT_FOUND_RESULT = new LocateResult(LocateStatus.NOT_FOUND, 0, 0, 0);
     private static final LocateResult SEARCH_LIMIT_RESULT =
             new LocateResult(LocateStatus.SEARCH_LIMIT_REACHED, 0, 0, 0);
@@ -97,6 +102,39 @@ public final class IrisStructureLocator {
                 || placementIndex.vanillaAliases.contains(normalizedKey);
     }
 
+    public static boolean hasLocatablePlacement(Engine engine, String key) {
+        if (engine == null || key == null || key.isBlank()) {
+            return false;
+        }
+        return locatableIndex(engine).normalizedKeys().contains(normalize(key));
+    }
+
+    public static boolean hasLocatableEditablePlacement(Engine engine, String key) {
+        if (engine == null || key == null || key.isBlank()) {
+            return false;
+        }
+        return locatableIndex(engine).normalizedEditableKeys().contains(normalize(key));
+    }
+
+    public static boolean hasLocatableNativePlacement(Engine engine, String key) {
+        if (engine == null || key == null || key.isBlank()) {
+            return false;
+        }
+        return locatableIndex(engine).normalizedNativeKeys().contains(normalize(key));
+    }
+
+    public static Set<String> locatableKeys(Engine engine) {
+        return locatableIndex(engine).keys();
+    }
+
+    public static Set<String> locatableEditableKeys(Engine engine) {
+        return locatableIndex(engine).editableKeys();
+    }
+
+    public static Set<String> locatableNativeKeys(Engine engine) {
+        return locatableIndex(engine).nativeKeys();
+    }
+
     public static boolean hasNativePlacement(Engine engine, String key) {
         if (engine == null || key == null || key.isBlank()) {
             return false;
@@ -126,6 +164,7 @@ public final class IrisStructureLocator {
     public static void invalidate(Engine engine) {
         if (engine != null) {
             INDEX_CACHE.invalidate(engine);
+            LOCATABLE_INDEX_CACHE.invalidate(engine);
         }
     }
 
@@ -796,7 +835,8 @@ public final class IrisStructureLocator {
         List<IrisStructurePlacement> concentricRings = new ArrayList<>();
         boolean hasDensity = false;
         for (IrisStructurePlacement placement : index(engine).placements) {
-            if (!matches(placement, key, engine.getData())) {
+            if (!isSearchablePlacement(engine, placement)
+                    || !matches(placement, key, engine.getData())) {
                 continue;
             }
             if (placement.getDistribution() == StructureDistribution.RANDOM_SPREAD) {
@@ -805,7 +845,7 @@ public final class IrisStructureLocator {
                         StructurePlacementGrid.placementSalt(placement)));
             } else if (placement.getDistribution() == StructureDistribution.CONCENTRIC_RINGS) {
                 concentricRings.add(placement);
-            } else if (isSearchableDensityPlacement(engine, placement)) {
+            } else if (placement.getDistribution() == StructureDistribution.DENSITY) {
                 hasDensity = true;
             }
         }
@@ -813,8 +853,18 @@ public final class IrisStructureLocator {
     }
 
     static boolean isSearchableDensityPlacement(Engine engine, IrisStructurePlacement placement) {
-        if (engine == null || placement == null || placement.getDistribution() != StructureDistribution.DENSITY
+        return placement != null
-                || !(placement.getDensity() > 0.0) || engine.getHeight() <= 0) {
+                && placement.getDistribution() == StructureDistribution.DENSITY
+                && isSearchablePlacement(engine, placement);
+    }
+
+    static boolean isSearchablePlacement(Engine engine, IrisStructurePlacement placement) {
+        if (engine == null || placement == null || placement.getDistribution() == null
+                || engine.getHeight() <= 0) {
+            return false;
+        }
+        if (placement.getDistribution() == StructureDistribution.DENSITY
+                && !(placement.getDensity() > 0.0)) {
             return false;
         }
         long worldMin = (long) engine.getMinHeight() + (placement.isUnderground() ? 1L : 0L);
@@ -952,6 +1002,64 @@ public final class IrisStructureLocator {
         return INDEX_CACHE.get(engine, ignored -> build(engine));
     }
 
+    private static LocatableIndex locatableIndex(Engine engine) {
+        if (engine == null) {
+            return EMPTY_LOCATABLE_INDEX;
+        }
+        return LOCATABLE_INDEX_CACHE.get(engine, ignored -> buildLocatableIndex(engine));
+    }
+
+    private static LocatableIndex buildLocatableIndex(Engine engine) {
+        IrisData data = engine.getData();
+        Set<String> keys = new LinkedHashSet<>();
+        Set<String> normalizedKeys = new LinkedHashSet<>();
+        Set<String> editableKeys = new LinkedHashSet<>();
+        Set<String> normalizedEditableKeys = new LinkedHashSet<>();
+        Set<String> nativeKeys = new LinkedHashSet<>();
+        Set<String> normalizedNativeKeys = new LinkedHashSet<>();
+        for (IrisStructurePlacement placement : index(engine).placements) {
+            if (!isSearchablePlacement(engine, placement)) {
+                continue;
+            }
+            if (placement.hasNativeStructures()) {
+                for (IrisNativeStructure source : placement.getNativeStructures()) {
+                    addLocatableKey(source.getStructure(), keys, normalizedKeys);
+                    addLocatableKey(source.getStructure(), nativeKeys, normalizedNativeKeys);
+                }
+                continue;
+            }
+            for (String structureKey : placement.getStructures()) {
+                IrisStructure structure = data.load(IrisStructure.class, structureKey, false);
+                if (structure == null) {
+                    throw new IllegalStateException(
+                            "Iris structure placement references missing structure '" + structureKey + "'");
+                }
+                addLocatableKey(structureKey, keys, normalizedKeys);
+                addLocatableKey(structureKey, editableKeys, normalizedEditableKeys);
+                addLocatableKey(structure.getLoadKey(), keys, normalizedKeys);
+                addLocatableKey(structure.getLoadKey(), editableKeys, normalizedEditableKeys);
+                addLocatableKey(structure.getVanillaSource(), keys, normalizedKeys);
+                addLocatableKey(structure.getVanillaSource(), editableKeys, normalizedEditableKeys);
+            }
+        }
+        return new LocatableIndex(
+                Collections.unmodifiableSet(keys),
+                Collections.unmodifiableSet(normalizedKeys),
+                Collections.unmodifiableSet(editableKeys),
+                Collections.unmodifiableSet(normalizedEditableKeys),
+                Collections.unmodifiableSet(nativeKeys),
+                Collections.unmodifiableSet(normalizedNativeKeys));
+    }
+
+    private static void addLocatableKey(String key, Set<String> keys, Set<String> normalizedKeys) {
+        if (key == null || key.isBlank()) {
+            return;
+        }
+        String trimmedKey = key.trim();
+        keys.add(trimmedKey);
+        normalizedKeys.add(normalize(trimmedKey));
+    }
+
     private static PlacementIndex build(Engine engine) {
         IrisData data = engine.getData();
         Set<String> loadKeys = new LinkedHashSet<>();
@@ -1112,6 +1220,11 @@ public final class IrisStructureLocator {
                                     List<IrisStructurePlacement> concentricRings, boolean hasDensity) {
     }
 
+    private record LocatableIndex(Set<String> keys, Set<String> normalizedKeys,
+                                  Set<String> editableKeys, Set<String> normalizedEditableKeys,
+                                  Set<String> nativeKeys, Set<String> normalizedNativeKeys) {
+    }
+
     private record ResolvedStart(int originX, int baseY, int originZ) {
     }
 

core/src/main/java/art/arcane/iris/util/common/director/specialhandlers/StructureHandler.java

@@ -18,42 +18,57 @@
 
 package art.arcane.iris.util.common.director.specialhandlers;
 
-import art.arcane.iris.core.nms.INMS;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.framework.IrisStructureLocator;
-import art.arcane.volmlib.util.collection.KList;
+import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
+import art.arcane.iris.engine.framework.StructureReachability;
+import art.arcane.iris.engine.object.IrisNativeStructureDecision;
+import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.spi.PlatformStructureHooks;
 import art.arcane.iris.util.common.director.DirectorParameterHandler;
+import art.arcane.volmlib.util.collection.KList;
 import art.arcane.volmlib.util.director.exceptions.DirectorParsingException;
+import org.bukkit.entity.Player;
 
-import java.util.stream.Collectors;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
 
 public class StructureHandler implements DirectorParameterHandler<String> {
     @Override
     public KList<String> getPossibilities() {
-        KList<String> keys = new KList<>();
+        Engine activeEngine = engine();
-
+        if (activeEngine == null) {
-        try {
+            return new KList<>();
-            for (String k : INMS.get().getStructureKeys()) {
-                if (k != null && !k.isEmpty()) {
-                    keys.addIfMissing(k);
-                }
-            }
-        } catch (Throwable ignored) {
         }
 
-        try {
+        boolean nativeGenerationEnabled = nativeStructureGenerationEnabled();
-            Engine e = engine();
+        PlatformStructureHooks structureHooks = IrisPlatforms.get().structureHooks();
-            if (e != null) {
+        Map<String, String> registeredKeys = distinctKeys(structureHooks.structureKeys());
-                for (String k : IrisStructureLocator.placedKeys(e)) {
+        Set<String> reachableKeys = StructureReachability.reachableKeys(activeEngine);
-                    if (k != null && !k.isEmpty()) {
+        Map<String, String> suggestions = new LinkedHashMap<>();
-                        keys.addIfMissing(k);
+
-                    }
+        for (Map.Entry<String, String> entry : registeredKeys.entrySet()) {
-                }
+            if (isEligibleRegisteredKey(activeEngine, entry.getValue(), entry.getKey(), reachableKeys,
+                    nativeGenerationEnabled)) {
+                suggestions.put(entry.getKey(), entry.getValue());
             }
-        } catch (Throwable ignored) {
         }
 
-        return keys;
+        Set<String> locatableKeys = IrisStructureLocator.locatableEditableKeys(activeEngine);
+        for (String key : locatableKeys) {
+            String normalizedKey = normalizeKey(key);
+            if (!normalizedKey.isEmpty()
+                    && !registeredKeys.containsKey(normalizedKey)
+                    && !IrisStructureLocator.hasNativePlacement(activeEngine, key)) {
+                suggestions.putIfAbsent(normalizedKey, key.trim());
+            }
+        }
+
+        return new KList<>(suggestions.values());
     }
 
     @Override
@@ -64,15 +79,12 @@ public class StructureHandler implements DirectorParameterHandler<String> {
     @Override
     public String parse(String in, boolean force) throws DirectorParsingException {
         KList<String> options = getPossibilities(in);
-
+        for (String option : options) {
-        if (options.isEmpty()) {
+            if (option.equalsIgnoreCase(in)) {
-            return in;
+                return option;
-        }
+            }
-        try {
-            return options.stream().filter((i) -> toString(i).equalsIgnoreCase(in)).collect(Collectors.toList()).get(0);
-        } catch (Throwable e) {
-            return in;
         }
+        return in;
     }
 
     @Override
@@ -86,4 +98,50 @@ public class StructureHandler implements DirectorParameterHandler<String> {
 
         return f == null ? "minecraft_ancient_city" : f;
     }
+
+    protected boolean nativeStructureGenerationEnabled() {
+        Player activePlayer = player();
+        return activePlayer != null && activePlayer.getWorld().canGenerateStructures();
+    }
+
+    private static Map<String, String> distinctKeys(List<String> keys) {
+        Map<String, String> distinct = new LinkedHashMap<>();
+        for (String key : keys) {
+            String normalizedKey = normalizeKey(key);
+            if (!normalizedKey.isEmpty()) {
+                distinct.putIfAbsent(normalizedKey, key.trim());
+            }
+        }
+        return distinct;
+    }
+
+    private static boolean isEligibleRegisteredKey(Engine engine, String key, String normalizedKey,
+                                                   Set<String> reachableKeys, boolean nativeGenerationEnabled) {
+        IrisNativeStructureDecision decision = NativeStructureGenerationPolicy.resolve(engine, key, false);
+        boolean nativePlacement = IrisStructureLocator.hasNativePlacement(engine, key);
+        boolean locatableNativePlacement = nativePlacement
+                && IrisStructureLocator.hasLocatableNativePlacement(engine, key);
+        boolean locatableEditableReplacement = !nativePlacement
+                && decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS
+                && IrisStructureLocator.hasLocatableEditablePlacement(engine, key);
+        return isEligibleRegisteredKey(
+                decision, nativePlacement, locatableNativePlacement, locatableEditableReplacement,
+                reachableKeys.contains(normalizedKey), nativeGenerationEnabled);
+    }
+
+    static boolean isEligibleRegisteredKey(IrisNativeStructureDecision decision, boolean nativePlacement,
+                                           boolean locatableNativePlacement,
+                                           boolean locatableEditableReplacement,
+                                           boolean reachable, boolean nativeGenerationEnabled) {
+        if (decision.status() == NativeStructureGenerationStatus.REPLACED_BY_IRIS) {
+            return locatableEditableReplacement
+                    || nativeGenerationEnabled && nativePlacement && locatableNativePlacement;
+        }
+        return nativeGenerationEnabled && decision.generate()
+                && (reachable || (nativePlacement && locatableNativePlacement));
+    }
+
+    private static String normalizeKey(String key) {
+        return key == null ? "" : key.trim().toLowerCase(Locale.ROOT);
+    }
 }

core/src/test/java/art/arcane/iris/engine/framework/IrisStructureLocatorContractTest.java

@@ -77,6 +77,70 @@ public class IrisStructureLocatorContractTest {
         assertFalse(IrisStructureLocator.isPlaced(engine, ""));
     }
 
+    @Test
+    public void locatablePlacementsExcludeDisabledDensityConfigurations() {
+        Engine disabled = densityEngine(0.0, false, -64, 384, -2032, 2032);
+        Engine active = densityEngine(0.01, false, -64, 384, -2032, 2032);
+
+        assertTrue(IrisStructureLocator.isPlaced(disabled, "test:density"));
+        assertFalse(IrisStructureLocator.hasLocatablePlacement(disabled, "test:density"));
+        assertTrue(IrisStructureLocator.locatableKeys(disabled).isEmpty());
+        assertTrue(IrisStructureLocator.hasLocatablePlacement(active, "test:density"));
+        assertTrue(IrisStructureLocator.locatableKeys(active).contains("test:density"));
+        assertFalse(IrisStructureLocator.hasLocatablePlacement(null, "test:density"));
+        assertTrue(IrisStructureLocator.locatableKeys(null).isEmpty());
+    }
+
+    @Test
+    public void locatablePlacementsExcludeEveryDistributionOutsideWorldHeight() {
+        Engine randomSpread = densityEngine(1.0, false, -64, 384, 400, 500);
+        randomSpread.getDimension().getStructures().get(0)
+                .setDistribution(StructureDistribution.RANDOM_SPREAD);
+        Engine concentricRings = densityEngine(1.0, false, -64, 384, 400, 500);
+        concentricRings.getDimension().getStructures().get(0)
+                .setDistribution(StructureDistribution.CONCENTRIC_RINGS);
+
+        assertFalse(IrisStructureLocator.hasLocatablePlacement(randomSpread, "test:density"));
+        assertFalse(IrisStructureLocator.hasLocatablePlacement(concentricRings, "test:density"));
+    }
+
+    @Test
+    public void locatableIndexIncludesAliasesAndSeparatesEditableFromNativePlacements() {
+        IrisData data = mock(IrisData.class);
+        IrisStructure structure = new IrisStructure();
+        structure.setLoadKey("test:city");
+        structure.setVanillaSource("source:city");
+        when(data.load(IrisStructure.class, "test:city_definition", false)).thenReturn(structure);
+
+        IrisStructurePlacement editable = new IrisStructurePlacement();
+        editable.getStructures().add("test:city_definition");
+        IrisStructurePlacement nativePlacement = new IrisStructurePlacement();
+        nativePlacement.getNativeStructures().add(new IrisNativeStructure()
+                .setStructure("source:native_city"));
+        IrisDimension dimension = mock(IrisDimension.class);
+        KList<IrisStructurePlacement> placements = new KList<>();
+        placements.add(editable);
+        placements.add(nativePlacement);
+        Engine engine = mock(Engine.class);
+        when(engine.getData()).thenReturn(data);
+        when(engine.getDimension()).thenReturn(dimension);
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.getHeight()).thenReturn(384);
+        when(dimension.getStructures()).thenReturn(placements);
+        when(dimension.getAllRegions(engine)).thenReturn(new KList<>());
+        when(dimension.getReachableBiomes(engine)).thenReturn(new KList<>());
+
+        assertEquals(Set.of("test:city_definition", "test:city", "source:city", "source:native_city"),
+                IrisStructureLocator.locatableKeys(engine));
+        assertEquals(Set.of("test:city_definition", "test:city", "source:city"),
+                IrisStructureLocator.locatableEditableKeys(engine));
+        assertEquals(Set.of("source:native_city"), IrisStructureLocator.locatableNativeKeys(engine));
+        assertTrue(IrisStructureLocator.hasLocatableEditablePlacement(engine, "SOURCE:CITY"));
+        assertFalse(IrisStructureLocator.hasLocatableEditablePlacement(engine, "source:native_city"));
+        assertTrue(IrisStructureLocator.hasLocatableNativePlacement(engine, "SOURCE:NATIVE_CITY"));
+        assertFalse(IrisStructureLocator.hasLocatableNativePlacement(engine, "source:city"));
+    }
+
     @Test
     public void suppressesVanillaIsFalseForNullEngine() {
         assertFalse(IrisStructureLocator.suppressesVanilla(null, "minecraft:ancient_city"));

core/src/test/java/art/arcane/iris/util/common/director/specialhandlers/StructureHandlerTest.java

@@ -0,0 +1,300 @@
+package art.arcane.iris.util.common.director.specialhandlers;
+
+import art.arcane.iris.core.loader.IrisData;
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.framework.IrisStructureLocator;
+import art.arcane.iris.engine.framework.StructureReachability;
+import art.arcane.iris.engine.object.IrisDimension;
+import art.arcane.iris.engine.object.IrisImportedStructureControl;
+import art.arcane.iris.engine.object.IrisNativeStructure;
+import art.arcane.iris.engine.object.IrisNativeStructureDecision;
+import art.arcane.iris.engine.object.IrisStructure;
+import art.arcane.iris.engine.object.IrisStructurePlacement;
+import art.arcane.iris.engine.object.IrisWorld;
+import art.arcane.iris.engine.object.NativeStructureGenerationStatus;
+import art.arcane.iris.engine.object.StructureDistribution;
+import art.arcane.iris.spi.IrisPlatform;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.spi.PlatformStructureHooks;
+import art.arcane.iris.spi.PlatformWorld;
+import art.arcane.volmlib.util.collection.KList;
+import art.arcane.volmlib.util.director.exceptions.DirectorParsingException;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class StructureHandlerTest {
+    @Test
+    public void registeredEligibilityMatchesFindExecutionTruthTable() {
+        IrisNativeStructureDecision replacement = decision(NativeStructureGenerationStatus.REPLACED_BY_IRIS);
+        IrisNativeStructureDecision generated = decision(NativeStructureGenerationStatus.GENERATE_NATIVE);
+        IrisNativeStructureDecision disabled = decision(NativeStructureGenerationStatus.DISABLED_BY_PACK);
+
+        assertTrue(StructureHandler.isEligibleRegisteredKey(
+                replacement, false, false, true, false, false));
+        assertFalse(StructureHandler.isEligibleRegisteredKey(
+                replacement, false, false, false, true, true));
+        assertTrue(StructureHandler.isEligibleRegisteredKey(
+                replacement, true, true, false, false, true));
+        assertFalse(StructureHandler.isEligibleRegisteredKey(
+                replacement, true, true, false, false, false));
+        assertTrue(StructureHandler.isEligibleRegisteredKey(
+                generated, true, true, false, false, true));
+        assertFalse(StructureHandler.isEligibleRegisteredKey(
+                generated, true, false, false, false, true));
+        assertTrue(StructureHandler.isEligibleRegisteredKey(
+                generated, false, false, false, true, true));
+        assertFalse(StructureHandler.isEligibleRegisteredKey(
+                generated, false, false, false, true, false));
+        assertFalse(StructureHandler.isEligibleRegisteredKey(
+                disabled, true, true, false, true, true));
+    }
+
+    @Test
+    public void requiresActiveIrisEngineBeforeReadingPlatformRegistries() throws DirectorParsingException {
+        IrisPlatforms.unbind();
+        TestStructureHandler handler = new TestStructureHandler(null, true);
+
+        assertTrue(handler.getPossibilities().isEmpty());
+        assertEquals("manual:structure", handler.parse("manual:structure", false));
+    }
+
+    @Test
+    public void filtersAndDeduplicatesSuggestionsForActiveEngine() {
+        IrisData data = mock(IrisData.class);
+        Engine engine = mock(Engine.class);
+        IrisDimension dimension = mock(IrisDimension.class);
+        IrisWorld world = mock(IrisWorld.class);
+        PlatformWorld platformWorld = mock(PlatformWorld.class);
+        IrisPlatform platform = mock(IrisPlatform.class);
+        PlatformStructureHooks hooks = mock(PlatformStructureHooks.class);
+        IrisImportedStructureControl control = new IrisImportedStructureControl();
+        control.getDisabled().add("pack:disabled");
+        control.getDisabled().add("pack:replacement");
+        control.getDisabled().add("pack:dormant_replacement");
+
+        KList<IrisStructurePlacement> placements = new KList<>();
+        placements.add(nativePlacement("pack:replacement", StructureDistribution.RANDOM_SPREAD, 1.0));
+        placements.add(nativePlacement("pack:dormant_replacement", StructureDistribution.DENSITY, 0.0));
+        placements.add(nativePlacement("pack:explicit", StructureDistribution.RANDOM_SPREAD, 1.0));
+        placements.add(nativePlacement("pack:dormant_explicit", StructureDistribution.DENSITY, 0.0));
+        placements.add(nativePlacement("pack:unregistered_native", StructureDistribution.RANDOM_SPREAD, 1.0));
+        placements.add(nativePlacement("iris:custom", StructureDistribution.RANDOM_SPREAD, 1.0));
+        placements.add(editablePlacement("iris:custom_definition"));
+        placements.add(editablePlacement("iris:collision_definition"));
+
+        IrisStructure custom = new IrisStructure();
+        custom.setLoadKey("iris:custom");
+        IrisStructure collision = new IrisStructure();
+        collision.setLoadKey("pack:collision");
+        when(data.load(IrisStructure.class, "iris:custom_definition", false)).thenReturn(custom);
+        when(data.load(IrisStructure.class, "iris:collision_definition", false)).thenReturn(collision);
+        when(engine.getData()).thenReturn(data);
+        when(engine.getDimension()).thenReturn(dimension);
+        when(engine.getWorld()).thenReturn(world);
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.getHeight()).thenReturn(384);
+        when(world.platformWorld()).thenReturn(platformWorld);
+        when(dimension.getImportedStructures()).thenReturn(control);
+        when(dimension.getStructures()).thenReturn(placements);
+        when(dimension.getAllRegions(engine)).thenReturn(new KList<>());
+        when(dimension.getReachableBiomes(engine)).thenReturn(new KList<>());
+        when(platform.structureHooks()).thenReturn(hooks);
+        when(hooks.structureKeys()).thenReturn(List.of(
+                "pack:reachable",
+                "PACK:REACHABLE",
+                "pack:unreachable",
+                "pack:disabled",
+                "pack:replacement",
+                "pack:dormant_replacement",
+                "pack:explicit",
+                "pack:dormant_explicit",
+                "PACK:COLLISION"));
+        when(hooks.reachableStructureKeys(platformWorld)).thenReturn(List.of("PACK:REACHABLE"));
+
+        IrisPlatforms.unbind();
+        IrisPlatforms.bind(platform);
+        try {
+            KList<String> possibilities = new TestStructureHandler(engine, true).getPossibilities();
+            Set<String> distinctPossibilities = new LinkedHashSet<>(possibilities);
+
+            assertEquals(Set.of(
+                    "pack:reachable",
+                    "pack:replacement",
+                    "pack:explicit",
+                    "iris:custom_definition",
+                    "iris:collision_definition"), distinctPossibilities);
+            assertEquals(distinctPossibilities.size(), possibilities.size());
+            assertFalse(possibilities.stream().anyMatch("pack:collision"::equalsIgnoreCase));
+            assertFalse(possibilities.contains("pack:unregistered_native"));
+            verify(hooks, times(1)).structureKeys();
+            verify(hooks, times(1)).reachableStructureKeys(platformWorld);
+        } finally {
+            IrisStructureLocator.invalidate(engine);
+            StructureReachability.invalidate(engine);
+            IrisPlatforms.unbind();
+        }
+    }
+
+    @Test
+    public void disabledWorldKeepsOnlyUnregisteredEditablePlacements() {
+        IrisData data = mock(IrisData.class);
+        Engine engine = mock(Engine.class);
+        IrisDimension dimension = mock(IrisDimension.class);
+        IrisWorld world = mock(IrisWorld.class);
+        PlatformWorld platformWorld = mock(PlatformWorld.class);
+        IrisPlatform platform = mock(IrisPlatform.class);
+        PlatformStructureHooks hooks = mock(PlatformStructureHooks.class);
+        IrisImportedStructureControl control = new IrisImportedStructureControl();
+        control.getDisabled().add("minecraft:replacement");
+
+        IrisStructure editable = new IrisStructure();
+        editable.setLoadKey("iris:editable");
+        IrisStructure replacement = new IrisStructure();
+        replacement.setLoadKey("iris:replacement");
+        replacement.setVanillaSource("minecraft:replacement");
+        KList<IrisStructurePlacement> placements = new KList<>();
+        placements.add(editablePlacement("iris:editable_definition"));
+        placements.add(editablePlacement("iris:replacement_definition"));
+        placements.add(nativePlacement("minecraft:explicit", StructureDistribution.RANDOM_SPREAD, 1.0));
+
+        when(data.load(IrisStructure.class, "iris:editable_definition", false)).thenReturn(editable);
+        when(data.load(IrisStructure.class, "iris:replacement_definition", false)).thenReturn(replacement);
+        when(engine.getData()).thenReturn(data);
+        when(engine.getDimension()).thenReturn(dimension);
+        when(engine.getWorld()).thenReturn(world);
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.getHeight()).thenReturn(384);
+        when(world.platformWorld()).thenReturn(platformWorld);
+        when(dimension.getImportedStructures()).thenReturn(control);
+        when(dimension.getStructures()).thenReturn(placements);
+        when(dimension.getAllRegions(engine)).thenReturn(new KList<>());
+        when(dimension.getReachableBiomes(engine)).thenReturn(new KList<>());
+        when(platform.structureHooks()).thenReturn(hooks);
+        when(hooks.structureKeys()).thenReturn(List.of(
+                "minecraft:replacement", "minecraft:explicit", "minecraft:reachable"));
+        when(hooks.reachableStructureKeys(platformWorld)).thenReturn(List.of("minecraft:reachable"));
+
+        IrisPlatforms.unbind();
+        IrisPlatforms.bind(platform);
+        try {
+            Set<String> possibilities = new LinkedHashSet<>(
+                    new TestStructureHandler(engine, false).getPossibilities());
+
+            assertEquals(Set.of(
+                    "minecraft:replacement",
+                    "iris:editable_definition",
+                    "iris:editable",
+                    "iris:replacement_definition",
+                    "iris:replacement"), possibilities);
+            assertFalse(possibilities.contains("minecraft:explicit"));
+            assertFalse(possibilities.contains("minecraft:reachable"));
+        } finally {
+            IrisStructureLocator.invalidate(engine);
+            StructureReachability.invalidate(engine);
+            IrisPlatforms.unbind();
+        }
+    }
+
+    @Test
+    public void propagatesRegistryFailures() {
+        Engine engine = mock(Engine.class);
+        IrisPlatform platform = mock(IrisPlatform.class);
+        PlatformStructureHooks hooks = mock(PlatformStructureHooks.class);
+        IllegalStateException failure = new IllegalStateException("registry unavailable");
+        when(platform.structureHooks()).thenReturn(hooks);
+        when(hooks.structureKeys()).thenThrow(failure);
+
+        IrisPlatforms.unbind();
+        IrisPlatforms.bind(platform);
+        try {
+            IllegalStateException thrown = assertThrows(
+                    IllegalStateException.class, () -> new TestStructureHandler(engine, true).getPossibilities());
+            assertSame(failure, thrown);
+        } finally {
+            IrisPlatforms.unbind();
+        }
+    }
+
+    @Test
+    public void completionUsesOneReachabilitySnapshotAndLocatableKeys() throws IOException {
+        Path sourcePath = Path.of(
+                "src/main/java/art/arcane/iris/util/common/director/specialhandlers/StructureHandler.java");
+        String source = Files.readString(sourcePath);
+        int methodStart = source.indexOf("public KList<String> getPossibilities()");
+        int methodEnd = source.indexOf("@Override\n    public String toString", methodStart);
+        String method = source.substring(methodStart, methodEnd);
+
+        assertEquals(1, occurrences(method, "StructureReachability.reachableKeys(activeEngine)"));
+        assertEquals(0, occurrences(method, "IrisStructureLocator.locatableKeys(activeEngine)"));
+        assertEquals(1, occurrences(method, "IrisStructureLocator.locatableEditableKeys(activeEngine)"));
+        assertTrue(method.indexOf("if (activeEngine == null)")
+                < method.indexOf("IrisPlatforms.get().structureHooks()"));
+        assertFalse(method.contains("INMS"));
+        assertFalse(method.contains("catch ("));
+    }
+
+    private static IrisNativeStructureDecision decision(NativeStructureGenerationStatus status) {
+        return new IrisNativeStructureDecision(status, 0, null, false, false, null, null);
+    }
+
+    private static IrisStructurePlacement nativePlacement(String key, StructureDistribution distribution,
+                                                          double density) {
+        IrisStructurePlacement placement = new IrisStructurePlacement();
+        placement.getNativeStructures().add(new IrisNativeStructure().setStructure(key));
+        placement.setDistribution(distribution);
+        placement.setDensity(density);
+        return placement;
+    }
+
+    private static IrisStructurePlacement editablePlacement(String key) {
+        IrisStructurePlacement placement = new IrisStructurePlacement();
+        placement.getStructures().add(key);
+        return placement;
+    }
+
+    private static int occurrences(String source, String target) {
+        int count = 0;
+        int offset = 0;
+        while ((offset = source.indexOf(target, offset)) >= 0) {
+            count++;
+            offset += target.length();
+        }
+        return count;
+    }
+
+    private static final class TestStructureHandler extends StructureHandler {
+        private final Engine activeEngine;
+        private final boolean nativeGenerationEnabled;
+
+        private TestStructureHandler(Engine activeEngine, boolean nativeGenerationEnabled) {
+            this.activeEngine = activeEngine;
+            this.nativeGenerationEnabled = nativeGenerationEnabled;
+        }
+
+        @Override
+        public Engine engine() {
+            return activeEngine;
+        }
+
+        @Override
+        protected boolean nativeStructureGenerationEnabled() {
+            return nativeGenerationEnabled;
+        }
+    }
+}