Refine Cave terrain environment and spawning (#14)

docs/AGE_PROFILES.md

@@ -40,6 +40,27 @@ profiles, not claims that Legacy had identically named terrain symbols.
 Every family retains a safe cobblestone arrival platform. An omitted terrain
 page still uses the deterministic seed-selected profile.
 
+### Cave terrain and Legacy
+
+Legacy's closest terrain generator is its Nether terrain symbol: it owns an
+Age-seeded octave-noise generator, accepts terrain/sea materials, and sets a
+sea level of 32. Legacy's separate Caves symbol instead registers a terrain
+alteration that carves additional caves; it is not a terrain generator.
+Minecraft 1.21.1 no longer has Legacy's 1.12.2 height and generation pipeline,
+so Rivencraft Cave terrain uses `minecraft:caves` noise and the modern Cave,
+Nether, and tagged modded Nether biome decorations. It cannot reproduce the
+exact Legacy noise or its older vertical layout. The Caves feature page
+remains a separate additive carver for other suitable terrain.
+
+Cave Ages search for safe spawn footing from Y=64 downward rather than using
+the cave roof; if necessary, the usual cloud platform is placed at Y=63.
+Weather is clear and Serene Seasons is disabled in Cave terrain. Authored
+Weather, Season, and Celestial pages (including time modifiers) are retained
+in the book but have no effect on the Cave Age; each adds 100 base instability.
+The same policy applies to randomly selected Cave terrain and persists through
+save/reload. Cave biome selections remain limited to Cave and Nether biomes;
+surface-biome completion is not used for Cave terrain.
+
 The separate **Floating Islands** feature page adds rare high-altitude island
 clusters above Standard, Amplified, Sky Islands, Flat, or Void terrain; it does
 not replace the terrain page. The feature is seeded by the Age and saved with the written

gradle.properties

@@ -36,7 +36,7 @@ mod_name=Rivencraft
 # The license of the mod. Review your options at https://choosealicense.com/. All Rights Reserved is the default.
 mod_license=LGPL-3.0-or-later
 # The mod version. Rivencraft uses the x.y.z.b policy documented in README.md.
-mod_version=0.6.6.9
+mod_version=0.6.7.0
 immersive_portals_version=6.0.7
 terrablender_version=4.1.0.8
 serene_seasons_version_id=pHEgQQUE

src/main/java/net/dnorberg/rivencraft/block/BookReceptacleBlock.java

@@ -97,7 +97,11 @@ public final class BookReceptacleBlock extends BaseEntityBlock {
         LinkTarget destination = stack.is(ModItems.LINKING_BOOK.get())
                 ? stack.get(ModDataComponents.LINK_TARGET.get())
                 : player instanceof ServerPlayer serverPlayer
-                    ? AgeDimensionService.resolve(serverPlayer, stack.get(ModDataComponents.AGE_REFERENCE.get())).orElse(null)
+                    ? AgeDimensionService.resolve(serverPlayer, stack.get(ModDataComponents.AGE_REFERENCE.get()),
+                            net.dnorberg.rivencraft.writing.OrderedWriting.EMPTY,
+                            !stack.getOrDefault(ModDataComponents.LINK_PROPERTIES.get(),
+                                    net.dnorberg.rivencraft.book.LinkProperties.NONE)
+                                    .has(net.dnorberg.rivencraft.book.LinkProperties.DISABLE_PLATFORM)).orElse(null)
                     : null;
         if (destination == null || server.getServer().getLevel(destination.location().dimension()) == null) {
             player.displayClientMessage(Component.translatable("message.rivencraft.descriptive_book.unavailable"), true);

src/main/java/net/dnorberg/rivencraft/book/AgeDefinition.java

@@ -118,4 +118,10 @@ public record AgeDefinition(
                 createdGameTime, dimensionId, spawn.immutable(), traits, plan, seasonMode,
                 randomFeatures, instability, instabilityPlan);
     }
+
+    /** A frozen authored profile takes precedence over the profile ID on old books. */
+    public boolean caveTerrain() {
+        return AgeBiomeSelection.isCave(plan == null
+                ? AgeRuntimeProfiles.resolve(generationProfile) : plan.runtimeProfile());
+    }
 }

src/main/java/net/dnorberg/rivencraft/book/AgeDimensionService.java

@@ -96,6 +96,11 @@ public final class AgeDimensionService {
 
     public static Optional<LinkTarget> resolve(ServerPlayer player, AgeReference reference,
                                                 OrderedWriting writing) {
+        return resolve(player, reference, writing, true);
+    }
+
+    public static Optional<LinkTarget> resolve(ServerPlayer player, AgeReference reference,
+                                                OrderedWriting writing, boolean generatePlatform) {
         AgeDefinition definition = AgeRegistrySavedData.resolveOrCreate(player.serverLevel(), reference, writing);
         if (AgeRegistrySavedData.get(player.serverLevel()).isDead(definition.id())) return Optional.empty();
         ServerLevel level = ensureLoaded(player.getServer(), definition);
@@ -106,7 +111,8 @@ public final class AgeDimensionService {
         BlockPos spawn = definition.spawn();
         if (spawn == null) {
             applyInitialCelestialPhase(level, definition);
-            spawn = createSafeSpawn(level, definition);
+            spawn = createSafeSpawn(level, definition, generatePlatform);
+            if (spawn == null) return Optional.empty();
             if (AgeFeatureSelection.resolved(definition.plan()).stream()
                     .anyMatch(choice -> choice.id().equals(AgeFeatureSelection.STAR_FISSURES))
                     || definition.randomFeatures().stream()
@@ -173,6 +179,10 @@ public final class AgeDimensionService {
     }
 
     private static void applyCelestialClock(ServerLevel level, AgeDefinition age) {
+        if (age.caveTerrain()) {
+            level.setDayTimePerTick(1.0F);
+            return;
+        }
         if (age.traits().hasStoppedCelestialCycle()) {
             // NeoForge rejects an exact zero rate. The smallest positive float
             // never advances the integer clock during a practical world
@@ -201,6 +211,7 @@ public final class AgeDimensionService {
     }
 
     private static void applyInitialCelestialPhase(ServerLevel level, AgeDefinition age) {
+        if (age.caveTerrain()) return;
         long phaseTime = (long)(age.traits().celestialPhase() * Level.TICKS_PER_DAY);
         if (AgeEnvironmentCompiler.hasWrittenPhase(age.plan())) {
             // Legacy's Nadir is midnight, while vanilla day time zero is sunrise.
@@ -219,21 +230,24 @@ public final class AgeDimensionService {
         return ResourceKey.create(net.minecraft.core.registries.Registries.DIMENSION, definition.dimensionId());
     }
 
-    private static BlockPos createSafeSpawn(ServerLevel level, AgeDefinition age) {
+    private static BlockPos createSafeSpawn(ServerLevel level, AgeDefinition age, boolean generatePlatform) {
         BlockPos floorCenter;
-        if (age.generationProfile().equals(AgeGenerationProfiles.CAVE)) {
+        if (age.caveTerrain()) {
             // Cave Ages are enclosed. Searching from the world ceiling would
             // select or expose their roof, so begin with the floor beneath a
             // player standing at Y=64 and search downward from there.
             floorCenter = highestFootedSurface(level, CAVE_SPAWN_SEARCH_Y - 1)
-                    .orElseGet(() -> fallbackSpawnFloor(level));
+                    .orElseGet(() -> generatePlatform ? fallbackSpawnFloor(level) : null);
         } else if (isNetherStyle(level)) {
-            floorCenter = netherSpawnFloor(level);
+            floorCenter = generatePlatform ? netherSpawnFloor(level)
+                    : highestFootedSurface(level, CAVE_SPAWN_SEARCH_Y - 1).orElse(null);
         } else {
-            floorCenter = highestFootedSurface(level).orElseGet(() -> fallbackSpawnFloor(level));
+            floorCenter = highestFootedSurface(level).orElseGet(() -> generatePlatform ? fallbackSpawnFloor(level) : null);
         }
 
-        for (int x = -PLATFORM_RADIUS; x <= PLATFORM_RADIUS; x++) {
+        if (floorCenter == null) return null;
+
+        if (generatePlatform) for (int x = -PLATFORM_RADIUS; x <= PLATFORM_RADIUS; x++) {
             for (int z = -PLATFORM_RADIUS; z <= PLATFORM_RADIUS; z++) {
                 BlockPos floor = floorCenter.offset(x, 0, z);
                 level.setBlock(floor, ModBlocks.CLOUD_PLATFORM.get().defaultBlockState(), 2);
@@ -244,6 +258,11 @@ public final class AgeDimensionService {
         }
 
         BlockPos spawn = floorCenter.above();
+        if (!generatePlatform) {
+            var safe = LinkingService.resolveDestination(level, spawn, true);
+            if (safe.isEmpty()) return null;
+            spawn = BlockPos.containing(safe.get());
+        }
         level.setDefaultSpawnPos(spawn, 0.0F);
         return spawn;
     }

src/main/java/net/dnorberg/rivencraft/book/AgeEnvironmentCompiler.java

@@ -10,13 +10,23 @@ public final class AgeEnvironmentCompiler {
 
     public static AgeTraits apply(AgeGenerationPlan plan, AgeTraits seeded) {
         if (plan == null) return seeded;
+        AgeTraits applied;
         if (plan.version() >= 4) {
             AgeTraits base = applyLegacy(plan, seeded);
             CelestialWriting ordered = orderedCelestial(plan, seeded);
-            return new AgeTraits(base.biomeDistribution(), base.lighting(), base.weather(),
+            applied = new AgeTraits(base.biomeDistribution(), base.lighting(), base.weather(),
                     ordered.period(), base.celestialAngle(), ordered.phase());
+        } else {
+            applied = applyLegacy(plan, seeded);
         }
-        return applyLegacy(plan, seeded);
+        return forTerrain(applied, plan.runtimeProfile());
+    }
+
+    /** Cave terrain has no exposed weather or meaningful sky clock, even with authored pages. */
+    public static AgeTraits forTerrain(AgeTraits traits, AgeRuntimeProfile profile) {
+        if (!AgeBiomeSelection.isCave(profile)) return traits;
+        return new AgeTraits(traits.biomeDistribution(), traits.lighting(), AgeTraits.Weather.OFF,
+                1.0D, 0.0F, 0.0F);
     }
 
     /** Version-3 plans keep their frozen, stage-sorted environment interpretation. */

src/main/java/net/dnorberg/rivencraft/book/AgeInstability.java

@@ -15,6 +15,7 @@ import net.minecraft.resources.ResourceLocation;
 public record AgeInstability(int version, int score, List<Contribution> breakdown) {
     public static final int CURRENT_VERSION = 2;
     private static final int BRIGHT_LIGHTING_COST = 500;
+    private static final int INEFFECTIVE_CAVE_PAGE_COST = 100;
     private static final int EXCESS_LEGACY_STRUCTURE_COST = 100;
     private static final int FORCED_STRUCTURE_BIOME_COST = 100;
     private static final Map<ResourceLocation, String> COUNTED_STRUCTURES = Map.ofEntries(
@@ -88,7 +89,19 @@ public record AgeInstability(int version, int score, List<Contribution> breakdow
     private static void addAuditedSymbolCosts(AgeGenerationPlan plan, RegistryAccess registries,
                                               List<Contribution> contributions) {
         Map<ResourceLocation, Integer> structureCounts = new HashMap<>();
+        boolean cave = AgeBiomeSelection.isCave(plan.runtimeProfile());
         for (AgeGenerationPlan.ResolvedSymbol symbol : plan.symbols()) {
+            if (cave) {
+                var role = symbol.semantics().role();
+                if (switch (role) {
+                    case WEATHER, SEASON, CELESTIAL, PERIOD_MODIFIER, PHASE_MODIFIER, ANGLE_MODIFIER -> true;
+                    default -> false;
+                }) {
+                    contributions.add(new Contribution("cave_ignored_" + role.id(), symbol.index(),
+                            INEFFECTIVE_CAVE_PAGE_COST,
+                            "Sky or weather page has no effect in Cave terrain"));
+                }
+            }
             if (symbol.semantics().role()
                     == net.dnorberg.rivencraft.writing.SymbolSemantics.Role.ENVIRONMENT
                     && symbol.semantics().value()

src/main/java/net/dnorberg/rivencraft/book/AgePersistenceGameTests.java

@@ -23,6 +23,31 @@ public final class AgePersistenceGameTests {
     private AgePersistenceGameTests() {
     }
 
+    @GameTest(template = "empty")
+    public static void modifierSeedChangePersistsWithoutChangingAgeIdentity(GameTestHelper helper) {
+        UUID id = UUID.randomUUID();
+        AgeDefinition original = AgeRegistrySavedData.resolveOrCreate(helper.getLevel(),
+                new AgeReference(id, "Reseed " + id));
+        AgeRegistrySavedData registry = AgeRegistrySavedData.get(helper.getLevel());
+        long newSeed = original.seed() == 987654321L ? 987654322L : 987654321L;
+        helper.assertTrue(registry.reseed(helper.getLevel().getServer(), id, newSeed),
+                "An unoccupied Age must accept a new seed");
+        AgeDefinition changed = registry.find(id).orElseThrow();
+        helper.assertValueEqual(changed.id(), original.id(), "Reseeding must preserve the Age identity");
+        helper.assertValueEqual(changed.dimensionId(), original.dimensionId(),
+                "Reseeding must preserve its dimension and existing chunk location");
+        helper.assertValueEqual(changed.seed(), newSeed, "The new generator seed must be saved");
+        AgeDefinition restored = AgeRegistrySavedData.load(
+                registry.save(new CompoundTag(), helper.getLevel().registryAccess()),
+                helper.getLevel().registryAccess()).find(id).orElseThrow();
+        helper.assertValueEqual(restored.seed(), newSeed, "The new seed must survive reload");
+        var ageLevel = AgeDimensionService.ensureLoaded(helper.getLevel().getServer(), changed);
+        helper.assertTrue(ageLevel != null, "The reseeded Age must reload");
+        helper.assertValueEqual(ageLevel.getSeed(), newSeed,
+                "The runtime level must use the saved seed for new chunks");
+        helper.succeed();
+    }
+
     @GameTest(template = "empty")
     public static void retiredAgeIdentitySurvivesSaveAndCannotLoad(GameTestHelper helper) {
         UUID id = UUID.randomUUID();

src/main/java/net/dnorberg/rivencraft/book/AgeRegistrySavedData.java

@@ -16,6 +16,7 @@ import net.minecraft.nbt.CompoundTag;
 import net.minecraft.nbt.ListTag;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.MinecraftServer;
 import net.minecraft.util.datafix.DataFixTypes;
 import net.minecraft.world.level.saveddata.SavedData;
 import net.neoforged.fml.ModList;
@@ -136,6 +137,32 @@ public final class AgeRegistrySavedData extends SavedData {
         return updated;
     }
 
+    /** Changes the generator for future chunks; existing chunk data is deliberately preserved. */
+    public boolean reseed(MinecraftServer server, UUID ageId, long seed) {
+        AgeDefinition previous = ages.get(ageId);
+        if (previous == null || isDead(ageId)) return false;
+        if (previous.seed() == seed) return true;
+        ServerLevel loaded = server.getLevel(AgeDimensionService.dimensionKey(previous));
+        if (loaded != null && !loaded.players().isEmpty()) return false;
+
+        // Legacy changes the Age's seed, not its already-written pages or selected traits.
+        // Keeping the frozen plan and feature list prevents a visited Age from changing
+        // its identity while newly generated chunks use the revised terrain noise.
+        AgeGenerationPlan oldPlan = previous.plan();
+        AgeGenerationPlan plan = oldPlan == null ? null : new AgeGenerationPlan(oldPlan.version(), seed,
+                oldPlan.writing(), oldPlan.symbols(), oldPlan.runtimeProfile(), oldPlan.biomeSelection(),
+                oldPlan.activeSymbolIndices(), oldPlan.writingInstability());
+        AgeDefinition changed = new AgeDefinition(previous.id(), previous.name(), seed,
+                previous.generationProfile(), previous.generationVersion(), previous.createdGameTime(),
+                previous.dimensionId(), previous.spawn(), previous.traits(), plan, previous.seasonMode(),
+                previous.randomFeatures(), previous.instability(), previous.instabilityPlan());
+        if (AgeDimensionService.unload(server, previous) == AgeDimensionService.UnloadResult.FAILED)
+            return false;
+        ages.put(ageId, changed);
+        setDirty();
+        return true;
+    }
+
     private AgeDefinition getOrCreate(AgeReference reference, OrderedWriting writing,
                                       long worldSeed, long createdGameTime, RegistryAccess registries) {
         AgeDefinition existing = ages.get(reference.id());
@@ -149,7 +176,9 @@ public final class AgeRegistrySavedData extends SavedData {
         ResourceLocation seedProfile = AgeRuntimeProfiles.selectForWriting(seed, writing, registries);
         AgeTraits traits = AgeTraits.select(seed);
         AgeGenerationPlan plan = AgeGenerationPlan.compile(writing, seed, seedProfile, traits, registries);
-        AgeTraits effectiveTraits = AgeEnvironmentCompiler.apply(plan, traits);
+        AgeTraits effectiveTraits = plan == null
+                ? AgeEnvironmentCompiler.forTerrain(traits, AgeRuntimeProfiles.resolve(seedProfile))
+                : AgeEnvironmentCompiler.apply(plan, traits);
         AgeInstability instability = AgeInstability.compute(plan, effectiveTraits, registries);
         AgeInstabilityPlan instabilityPlan = AgeInstabilityPlan.select(instability, seed);
         AgeDefinition created = new AgeDefinition(
@@ -163,7 +192,8 @@ public final class AgeRegistrySavedData extends SavedData {
                 null,
                 effectiveTraits,
                 plan,
-                AgeSeasonMode.select(plan, seed, ModList.get().isLoaded("sereneseasons")),
+                AgeSeasonMode.select(plan, seed, ModList.get().isLoaded("sereneseasons"),
+                        plan == null ? AgeRuntimeProfiles.resolve(seedProfile) : plan.runtimeProfile()),
                 plan == null ? AgeFeatureSelection.randomChoices(seed,
                         AgeRuntimeProfiles.resolve(seedProfile), registries) : List.of(),
                 instability,

src/main/java/net/dnorberg/rivencraft/book/AgeSeasonMode.java

@@ -19,6 +19,12 @@ public enum AgeSeasonMode {
 
     /** An omitted page is selected once when an Age is created with Serene installed. */
     public static AgeSeasonMode select(AgeGenerationPlan plan, long ageSeed, boolean sereneInstalled) {
+        return select(plan, ageSeed, sereneInstalled, plan == null ? null : plan.runtimeProfile());
+    }
+
+    public static AgeSeasonMode select(AgeGenerationPlan plan, long ageSeed, boolean sereneInstalled,
+                                       AgeRuntimeProfile profile) {
+        if (profile != null && AgeBiomeSelection.isCave(profile)) return NO_SEASONS;
         if (hasAuthoredPage(plan)) return from(plan);
         return sereneInstalled ? LegacyRankChoice.choose(new Random(ageSeed ^ RANDOM_SALT), List.of(
                 new LegacyRankChoice.Option<>(SEASONS, 1),
@@ -31,6 +37,7 @@ public enum AgeSeasonMode {
 
     /** Existing Ages without a stored choice retain their old cycling behavior. */
     public static AgeSeasonMode from(AgeDefinition age) {
+        if (age.caveTerrain()) return NO_SEASONS;
         return age.seasonMode() == null ? from(age.plan()) : age.seasonMode();
     }
 
@@ -49,6 +56,7 @@ public enum AgeSeasonMode {
 
     public static AgeSeasonMode from(AgeGenerationPlan plan) {
         if (plan == null) return SEASONS;
+        if (AgeBiomeSelection.isCave(plan.runtimeProfile())) return NO_SEASONS;
         return plan.activeSymbols().stream()
                 .filter(symbol -> symbol.semantics().role() == SymbolSemantics.Role.SEASON)
                 .map(symbol -> valueOf(((SymbolSemantics.ChoiceValue) symbol.semantics().value())
@@ -58,6 +66,7 @@ public enum AgeSeasonMode {
 
     public static void validate(AgeGenerationPlan plan) {
         if (plan == null) return;
+        if (AgeBiomeSelection.isCave(plan.runtimeProfile())) return;
         if (hasAuthoredPage(plan) && from(plan) != NO_SEASONS
                 && !ModList.get().isLoaded("sereneseasons")) {
             throw new IllegalArgumentException("This seasonal page requires Serene Seasons to create the Age");

src/main/java/net/dnorberg/rivencraft/book/AgeWeatherService.java

@@ -26,7 +26,7 @@ public final class AgeWeatherService {
             return;
         }
 
-        AgeTraits.Weather weather = age.traits().weather();
+        AgeTraits.Weather weather = age.caveTerrain() ? AgeTraits.Weather.OFF : age.traits().weather();
         if (weather == AgeTraits.Weather.NORMAL) {
             STATES.remove(level);
             return;

src/main/java/net/dnorberg/rivencraft/book/CaveTerrainGameTests.java

@@ -0,0 +1,90 @@
+package net.dnorberg.rivencraft.book;
+
+import java.util.List;
+import java.util.UUID;
+import net.dnorberg.rivencraft.Rivencraft;
+import net.dnorberg.rivencraft.writing.OrderedWriting;
+import net.dnorberg.rivencraft.writing.SymbolReference;
+import net.dnorberg.rivencraft.writing.WritingEntry;
+import net.minecraft.gametest.framework.GameTest;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.level.biome.Biomes;
+import net.neoforged.neoforge.gametest.GameTestHolder;
+import net.neoforged.neoforge.gametest.PrefixGameTestTemplate;
+
+/** Focused Cave terrain writing and persisted-generation coverage for issue #14. */
+@GameTestHolder(Rivencraft.MOD_ID)
+@PrefixGameTestTemplate(false)
+public final class CaveTerrainGameTests {
+    private CaveTerrainGameTests() {}
+
+    @GameTest(template = "empty")
+    public static void caveSkyAndWeatherPagesCostInstabilityButDoNotApply(GameTestHelper helper) {
+        OrderedWriting cave = writing("terrain/cave", "biome/lush_caves", "biome/nether_wastes",
+                "biome/tiled", "weather/storm", "season/eternal_winter", "period/zero",
+                "celestial/normal_time");
+        AgeTraits seeded = new AgeTraits(AgeTraits.BiomeDistribution.SINGLE, AgeTraits.Lighting.NORMAL,
+                AgeTraits.Weather.ALWAYS, 0.5D, 0.0F, 0.25F);
+        var registries = helper.getLevel().registryAccess();
+        AgeGenerationPlan plan = AgeGenerationPlan.compile(cave, 42L, AgeGenerationProfiles.CAVE,
+                seeded, registries);
+        AgeTraits applied = AgeEnvironmentCompiler.apply(plan, seeded);
+        helper.assertValueEqual(applied.weather(), AgeTraits.Weather.OFF, "Cave weather must be off");
+        helper.assertValueEqual(applied.celestialPeriod(), 1.0D, "Cave time pages must not alter the clock");
+        helper.assertValueEqual(applied.celestialPhase(), 0.0F, "Cave time pages must not set a phase");
+        helper.assertValueEqual(AgeSeasonMode.select(plan, 42L, true), AgeSeasonMode.NO_SEASONS,
+                "Cave seasons must be disabled even when Serene Seasons is present");
+        helper.assertValueEqual(plan.biomeSelection().biomes(),
+                List.of(Biomes.LUSH_CAVES.location(), Biomes.NETHER_WASTES.location()),
+                "Cave writing must retain exactly its cave and Nether biomes");
+        AgeInstability instability = AgeInstability.compute(plan, applied, registries);
+        helper.assertValueEqual(instability.breakdown().stream()
+                        .filter(part -> part.reason().startsWith("cave_ignored_")).count(), 4L,
+                "Each ineffective weather, season, period, and celestial page must add instability");
+        helper.assertValueEqual(AgeInstability.compute(AgeGenerationPlan.load(plan.save()), applied, registries),
+                instability, "Cave page penalties must survive plan reload");
+
+        AgeGenerationPlan surfaceCaves = AgeGenerationPlan.compile(writing("terrain/standard", "feature/caves"),
+                42L, AgeGenerationProfiles.STANDARD, seeded, registries);
+        helper.assertTrue(!AgeBiomeSelection.isCave(surfaceCaves.runtimeProfile())
+                        && AgeFeatureSelection.resolved(surfaceCaves).stream()
+                        .anyMatch(choice -> AgeFeatureSelection.caves(choice.id())),
+                "The separate Caves feature page must still add caves to surface terrain");
+        helper.succeed();
+    }
+
+    @GameTest(template = "empty", timeoutTicks = 600)
+    public static void authoredCaveBiomeAndSpawnSurviveSavedDataReload(GameTestHelper helper) {
+        var player = helper.makeMockServerPlayerInLevel();
+        AgeReference reference = new AgeReference(UUID.randomUUID(), "Cave issue 14 " + UUID.randomUUID());
+        AgeDimensionService.resolve(player, reference,
+                writing("terrain/cave", "biome/nether_wastes", "biome/single")).orElseThrow();
+        var registry = AgeRegistrySavedData.get(helper.getLevel());
+        AgeDefinition age = registry.find(reference.id()).orElseThrow();
+        helper.assertTrue(age.caveTerrain(), "The Age must retain Cave terrain");
+        helper.assertTrue(age.spawn() != null && age.spawn().getY() <= 64,
+                "Cave spawn search must start at Y=64, not atop the roof");
+        helper.assertValueEqual(age.traits().weather(), AgeTraits.Weather.OFF,
+                "A new Cave Age must persist disabled weather");
+        helper.assertValueEqual(age.seasonMode(), AgeSeasonMode.NO_SEASONS,
+                "A new Cave Age must persist disabled seasons");
+        AgeDefinition reloaded = AgeRegistrySavedData.load(
+                registry.save(new CompoundTag(), helper.getLevel().registryAccess()),
+                helper.getLevel().registryAccess()).find(reference.id()).orElseThrow();
+        helper.assertValueEqual(reloaded, age, "Saved Cave biome, spawn, and environment must survive reload");
+        helper.assertValueEqual(reloaded.plan().biomeSelection().biomes(),
+                List.of(Biomes.NETHER_WASTES.location()),
+                "The generated Cave Age must preserve its authored-only Nether pool");
+        helper.succeed();
+    }
+
+    private static OrderedWriting writing(String... pages) {
+        var entries = new java.util.ArrayList<WritingEntry>();
+        entries.add(WritingEntry.linkPanel());
+        for (String page : pages) entries.add(WritingEntry.symbol(new SymbolReference(
+                ResourceLocation.parse("rivencraft:" + page))));
+        return new OrderedWriting(entries);
+    }
+}

src/main/java/net/dnorberg/rivencraft/book/LinkProperties.java

@@ -11,11 +11,15 @@ import net.minecraft.network.chat.Component;
 /** Flags written into a Link Panel and carried by books assembled from it. */
 public record LinkProperties(int flags) {
     public static final int DISARM = 1;
-    /** Retained only to read pre-0.4.7.1 test books; no longer generated or applied. */
+    /** Retained to read older test books; a newly edited book uses DISABLE_PLATFORM instead. */
     public static final int GENERATE_PLATFORM = 2;
     public static final int MAINTAIN_MOMENTUM = 4;
     public static final int INTRA_LINKING = 8;
-    private static final int ALL_FLAGS = DISARM | GENERATE_PLATFORM | MAINTAIN_MOMENTUM | INTRA_LINKING;
+    public static final int INTRA_LINKING_ONLY = 16;
+    public static final int RELATIVE_LINK = 32;
+    public static final int DISABLE_PLATFORM = 64;
+    private static final int ALL_FLAGS = DISARM | GENERATE_PLATFORM | MAINTAIN_MOMENTUM | INTRA_LINKING
+            | INTRA_LINKING_ONLY | RELATIVE_LINK | DISABLE_PLATFORM;
     public static final LinkProperties NONE = new LinkProperties(0);
     public static final Codec<LinkProperties> CODEC = Codec.intRange(0, ALL_FLAGS).xmap(
             LinkProperties::new, LinkProperties::flags);
@@ -35,13 +39,16 @@ public record LinkProperties(int flags) {
 
     /** Intra Linking only governs Linking Books; a Descriptive Book treats that panel as ordinary. */
     public LinkProperties forDescriptiveBook() {
-        return new LinkProperties(flags & ~INTRA_LINKING);
+        return new LinkProperties(flags & ~(INTRA_LINKING | INTRA_LINKING_ONLY));
     }
 
     public void appendTooltip(List<Component> lines) {
         if (has(DISARM)) lines.add(propertyName("disarm"));
         if (has(MAINTAIN_MOMENTUM)) lines.add(propertyName("maintain_momentum"));
         if (has(INTRA_LINKING)) lines.add(propertyName("intra_linking"));
+        if (has(INTRA_LINKING_ONLY)) lines.add(propertyName("intra_linking_only"));
+        if (has(RELATIVE_LINK)) lines.add(propertyName("relative_link"));
+        if (has(DISABLE_PLATFORM)) lines.add(propertyName("disable_platform"));
     }
 
     private static Component propertyName(String name) {
@@ -54,6 +61,9 @@ public record LinkProperties(int flags) {
             case DISARM -> propertyName("disarm");
             case MAINTAIN_MOMENTUM -> propertyName("maintain_momentum");
             case INTRA_LINKING -> propertyName("intra_linking");
+            case INTRA_LINKING_ONLY -> propertyName("intra_linking_only");
+            case RELATIVE_LINK -> propertyName("relative_link");
+            case DISABLE_PLATFORM -> propertyName("disable_platform");
             default -> throw new IllegalArgumentException("Unknown link property flag: " + flag);
         };
     }

src/main/java/net/dnorberg/rivencraft/book/LinkingService.java

@@ -86,7 +86,10 @@ public final class LinkingService {
         if (destinationLevel == null) {
             return LinkResult.MISSING_DIMENSION;
         }
-        Optional<Vec3> destination = resolveDestination(destinationLevel, target.location().pos(), true);
+        if (properties.has(LinkProperties.INTRA_LINKING_ONLY) && destinationLevel != player.serverLevel())
+            return LinkResult.INTRA_ONLY;
+        BlockPos origin = landingOrigin(player, destinationLevel, target, properties);
+        Optional<Vec3> destination = resolveDestination(destinationLevel, origin, true);
         if (destination.isEmpty()) {
             return LinkResult.NO_SAFE_DESTINATION;
         }
@@ -105,7 +108,10 @@ public final class LinkingService {
         ServerLevel destinationLevel = player.getServer().getLevel(target.location().dimension());
         if (destinationLevel == null) return LinkResult.MISSING_DIMENSION;
         boolean instant = destinationChunksLoaded(destinationLevel, target.location().pos());
-        Optional<Vec3> destination = resolveDestination(destinationLevel, target.location().pos(), true);
+        if (properties.has(LinkProperties.INTRA_LINKING_ONLY) && destinationLevel != player.serverLevel())
+            return LinkResult.INTRA_ONLY;
+        Optional<Vec3> destination = resolveDestination(destinationLevel,
+                landingOrigin(player, destinationLevel, target, properties), true);
         if (destination.isEmpty()) return LinkResult.NO_SAFE_DESTINATION;
         Vec3 momentum = player.getDeltaMovement();
         if (properties.has(LinkProperties.DISARM)) dropInventoryAtSource(player);
@@ -121,11 +127,15 @@ public final class LinkingService {
         if (destinationLevel == null) {
             return LinkResult.MISSING_DIMENSION;
         }
-        if (destinationLevel == player.level() && !properties.has(LinkProperties.INTRA_LINKING))
+        if (properties.has(LinkProperties.INTRA_LINKING_ONLY) && destinationLevel != player.serverLevel())
+            return LinkResult.INTRA_ONLY;
+        if (destinationLevel == player.level() && !properties.has(LinkProperties.INTRA_LINKING)
+                && !properties.has(LinkProperties.INTRA_LINKING_ONLY))
             return LinkResult.INTRA_LINKING_REQUIRED;
 
         boolean instant = !portal || destinationChunksLoaded(destinationLevel, target.location().pos());
-        Optional<Vec3> destination = resolveDestination(destinationLevel, target.location().pos(), requiresFooting);
+        Optional<Vec3> destination = resolveDestination(destinationLevel,
+                landingOrigin(player, destinationLevel, target, properties), requiresFooting);
         if (destination.isEmpty()) {
             return LinkResult.NO_SAFE_DESTINATION;
         }
@@ -139,6 +149,17 @@ public final class LinkingService {
         return LinkResult.SUCCESS;
     }
 
+    /** Legacy relative links retain the traveller's offset from the source spawn. */
+    private static BlockPos landingOrigin(ServerPlayer player, ServerLevel destinationLevel,
+                                          LinkTarget target, LinkProperties properties) {
+        if (!properties.has(LinkProperties.RELATIVE_LINK)) return target.location().pos();
+        BlockPos sourceSpawn = player.serverLevel().getSharedSpawnPos();
+        BlockPos destinationSpawn = destinationLevel.getSharedSpawnPos();
+        BlockPos departure = player.blockPosition();
+        return destinationSpawn.offset(departure.getX() - sourceSpawn.getX(),
+                departure.getY() - sourceSpawn.getY(), departure.getZ() - sourceSpawn.getZ());
+    }
+
     /** Drop each inventory stack as an item entity at the departure point. */
     private static void dropInventoryAtSource(ServerPlayer player) {
         var inventory = player.getInventory();
@@ -263,6 +284,7 @@ public final class LinkingService {
         SUCCESS,
         MISSING_DIMENSION,
         INTRA_LINKING_REQUIRED,
+        INTRA_ONLY,
         NO_SAFE_DESTINATION
     }
 }

src/main/java/net/dnorberg/rivencraft/client/screen/LinkModifierScreen.java

@@ -1,63 +1,121 @@
 package net.dnorberg.rivencraft.client.screen;
 
+import net.dnorberg.rivencraft.Rivencraft;
 import net.dnorberg.rivencraft.book.LinkProperties;
 import net.dnorberg.rivencraft.menu.LinkModifierMenu;
 import net.dnorberg.rivencraft.network.SetLinkModifierTitlePayload;
+import net.dnorberg.rivencraft.network.SetLinkModifierSeedPayload;
 import net.dnorberg.rivencraft.registry.ModDataComponents;
-import net.dnorberg.rivencraft.registry.ModItems;
 import net.minecraft.client.gui.GuiGraphics;
-import net.minecraft.client.gui.components.Button;
 import net.minecraft.client.gui.components.EditBox;
+import net.minecraft.client.gui.components.Tooltip;
 import net.minecraft.client.gui.screens.inventory.AbstractContainerScreen;
 import net.minecraft.core.component.DataComponents;
 import net.minecraft.network.chat.Component;
+import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.entity.player.Inventory;
 import net.minecraft.world.item.ItemStack;
 import net.neoforged.neoforge.network.PacketDistributor;
 
+/** Legacy single-slot layout, with server-owned link options. */
 public final class LinkModifierScreen extends AbstractContainerScreen<LinkModifierMenu> {
+    private static final ResourceLocation BACKGROUND = ResourceLocation.fromNamespaceAndPath(
+            Rivencraft.MOD_ID, "textures/gui/link_modifier_legacy.png");
+    private static final int[] FLAGS = {LinkProperties.DISARM, LinkProperties.INTRA_LINKING,
+            LinkProperties.INTRA_LINKING_ONLY, LinkProperties.MAINTAIN_MOMENTUM,
+            LinkProperties.RELATIVE_LINK, LinkProperties.DISABLE_PLATFORM};
+    private static final int[] IDS = {LinkModifierMenu.TOGGLE_DISARM, LinkModifierMenu.TOGGLE_INTRA,
+            LinkModifierMenu.TOGGLE_INTRA_ONLY, LinkModifierMenu.TOGGLE_MOMENTUM,
+            LinkModifierMenu.TOGGLE_RELATIVE, LinkModifierMenu.TOGGLE_PLATFORM};
     private EditBox titleInput;
-    private Button disarm;
-    private Button momentum;
-    private Button intra;
-    private Button retire;
+    private EditBox seedInput;
     private ItemStack lastBook = ItemStack.EMPTY;
+    private long lastSeed = Long.MIN_VALUE;
 
     public LinkModifierScreen(LinkModifierMenu menu, Inventory inventory, Component title) {
         super(menu, inventory, title);
         imageWidth = 176;
-        imageHeight = 194;
+        imageHeight = 166;
         inventoryLabelX = 8;
-        inventoryLabelY = 99;
+        inventoryLabelY = 72;
     }
 
     @Override protected void init() {
         super.init();
-        titleInput = new EditBox(font, leftPos + 8, topPos + 54, 160, 14,
+        titleInput = new EditBox(font, leftPos + 80, topPos + 56, 87, 14,
                 Component.translatable("screen.rivencraft.link_modifier.title"));
         titleInput.setMaxLength(32);
         titleInput.setResponder(value -> PacketDistributor.sendToServer(
                 new SetLinkModifierTitlePayload(menu.containerId, value)));
         addRenderableWidget(titleInput);
-        disarm = addRenderableWidget(Button.builder(Component.empty(), button -> click(LinkModifierMenu.TOGGLE_DISARM))
-                .bounds(leftPos + 8, topPos + 74, 76, 20).build());
-        momentum = addRenderableWidget(Button.builder(Component.empty(), button -> click(LinkModifierMenu.TOGGLE_MOMENTUM))
-                .bounds(leftPos + 92, topPos + 74, 76, 20).build());
-        intra = addRenderableWidget(Button.builder(Component.empty(), button -> click(LinkModifierMenu.TOGGLE_INTRA))
-                .bounds(leftPos + 8, topPos + 18, 64, 20).build());
-        retire = addRenderableWidget(Button.builder(Component.empty(), button -> click(LinkModifierMenu.DELETE_AGE))
-                .bounds(leftPos + 104, topPos + 18, 64, 20).build());
+        seedInput = new EditBox(font, leftPos + 80, topPos + 15, 87, 14,
+                Component.translatable("screen.rivencraft.link_modifier.seed"));
+        seedInput.setMaxLength(21);
+        seedInput.setTooltip(Tooltip.create(Component.translatable("screen.rivencraft.link_modifier.seed_warning")));
+        addRenderableWidget(seedInput);
         refreshControls();
     }
 
     private void click(int id) {
-        if (minecraft != null && minecraft.gameMode != null) {
+        if (minecraft != null && minecraft.gameMode != null)
             minecraft.gameMode.handleInventoryButtonClick(menu.containerId, id);
-        }
     }
 
     @Override protected void containerTick() { refreshControls(); }
 
+    private void submitSeed() {
+        if (seedInput.visible && !seedInput.getValue().equals(Long.toString(menu.seed())))
+            PacketDistributor.sendToServer(new SetLinkModifierSeedPayload(menu.containerId, seedInput.getValue()));
+    }
+
+    @Override public boolean keyPressed(int keyCode, int scanCode, int modifiers) {
+        if (seedInput.isFocused()) {
+            if (keyCode == 257 || keyCode == 335) submitSeed();
+            else if (keyCode != 256) seedInput.keyPressed(keyCode, scanCode, modifiers);
+            if (keyCode == 256 || keyCode == 257 || keyCode == 335) {
+                setFocused(null);
+                seedInput.setFocused(false);
+            }
+            return true;
+        }
+        if (titleInput.isFocused()) {
+            if (keyCode == 256) {
+                setFocused(null);
+                titleInput.setFocused(false);
+            } else titleInput.keyPressed(keyCode, scanCode, modifiers);
+            return true;
+        }
+        return super.keyPressed(keyCode, scanCode, modifiers);
+    }
+
+    @Override public boolean mouseClicked(double mouseX, double mouseY, int button) {
+        if (seedInput.isFocused() && (mouseX < seedInput.getX() || mouseX >= seedInput.getX() + seedInput.getWidth()
+                || mouseY < seedInput.getY() || mouseY >= seedInput.getY() + seedInput.getHeight())) {
+            submitSeed();
+            setFocused(null);
+            seedInput.setFocused(false);
+        }
+        if (button == 0) {
+            for (int index = 0; index < FLAGS.length; index++) {
+                if (inside(mouseX, mouseY, 5 + (index / 3) * 20, 10 + (index % 3) * 20, 18, 18)) {
+                    if (!menu.book().isEmpty()) click(IDS[index]);
+                    return true;
+                }
+            }
+            if (menu.canDelete(minecraft.player)
+                    && inside(mouseX, mouseY, menu.awaitingDeletionConfirmation() ? 140 : 120, 32, 18, 18)) {
+                click(LinkModifierMenu.DELETE_AGE);
+                return true;
+            }
+        }
+        return super.mouseClicked(mouseX, mouseY, button);
+    }
+
+    private boolean inside(double mouseX, double mouseY, int x, int y, int width, int height) {
+        return mouseX >= leftPos + x && mouseX < leftPos + x + width
+                && mouseY >= topPos + y && mouseY < topPos + y + height;
+    }
+
     private void refreshControls() {
         ItemStack book = menu.book();
         if (!ItemStack.isSameItemSameComponents(book, lastBook) && !titleInput.isFocused()) {
@@ -67,39 +125,59 @@ public final class LinkModifierScreen extends AbstractContainerScreen<LinkModifi
         }
         boolean present = !book.isEmpty();
         titleInput.setEditable(present);
-        LinkProperties properties = book.getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE);
-        disarm.active = present;
-        disarm.setMessage(Component.literal("Disarm " + (properties.has(LinkProperties.DISARM) ? "✓" : "×")));
-        momentum.active = present;
-        momentum.setMessage(Component.literal("Momentum " + (properties.has(LinkProperties.MAINTAIN_MOMENTUM) ? "✓" : "×")));
-        intra.visible = book.is(ModItems.LINKING_BOOK.get());
-        intra.setMessage(Component.literal("Intra " + (properties.has(LinkProperties.INTRA_LINKING) ? "✓" : "×")));
-        retire.visible = menu.canDelete(minecraft.player);
-        retire.setMessage(Component.translatable(menu.awaitingDeletionConfirmation()
-                ? "screen.rivencraft.link_modifier.confirm" : "screen.rivencraft.link_modifier.retire"));
+        seedInput.visible = menu.hasSeed();
+        seedInput.setEditable(menu.hasSeed());
+        if (seedInput.visible && !seedInput.isFocused() && (lastSeed != menu.seed()
+                || !ItemStack.isSameItemSameComponents(book, lastBook))) {
+            lastSeed = menu.seed();
+            seedInput.setValue(Long.toString(lastSeed));
+        }
     }
 
     @Override protected void renderBg(GuiGraphics graphics, float partialTick, int mouseX, int mouseY) {
-        graphics.fill(leftPos, topPos, leftPos + imageWidth, topPos + imageHeight, 0xFFD6C7A7);
-        graphics.renderOutline(leftPos, topPos, imageWidth, imageHeight, 0xFF493C34);
-        graphics.fill(leftPos + 78, topPos + 28, leftPos + 98, topPos + 48, 0xFF83785F);
-        graphics.renderOutline(leftPos + 77, topPos + 27, 22, 22, 0xFF493C34);
-        for (int row = 0; row < 3; row++) for (int col = 0; col < 9; col++)
-            slotBackground(graphics, 8 + col * 18, 112 + row * 18);
-        for (int col = 0; col < 9; col++) slotBackground(graphics, 8 + col * 18, 170);
+        graphics.blit(BACKGROUND, leftPos, topPos, 0, 0, imageWidth, imageHeight, 256, 256);
+        LinkProperties properties = menu.book().getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE);
+        for (int index = 0; index < FLAGS.length; index++)
+            square(graphics, 5 + (index / 3) * 20, 10 + (index % 3) * 20,
+                    properties.has(FLAGS[index]), false);
+        if (menu.canDelete(minecraft.player)) {
+            square(graphics, 120, 32, menu.awaitingDeletionConfirmation(), false);
+            if (menu.awaitingDeletionConfirmation()) square(graphics, 140, 32, false, true);
+        }
     }
 
-    private void slotBackground(GuiGraphics graphics, int x, int y) {
-        graphics.fill(leftPos + x - 1, topPos + y - 1, leftPos + x + 17, topPos + y + 17, 0xFF81745C);
+    private void square(GuiGraphics graphics, int x, int y, boolean selected, boolean danger) {
+        int left = leftPos + x;
+        int top = topPos + y;
+        graphics.fill(left, top, left + 18, top + 18, 0xFFAAAAAA);
+        graphics.fill(left + 2, top + 2, left + 17, top + 17,
+                danger ? 0xFFAA5555 : selected ? 0xFFBBBBBB : 0xFF777777);
     }
 
     @Override protected void renderLabels(GuiGraphics graphics, int mouseX, int mouseY) {
-        graphics.drawString(font, title, 8, 6, 0xFF332722, false);
-        graphics.drawString(font, playerInventoryTitle, inventoryLabelX, inventoryLabelY, 0xFF332722, false);
+        graphics.drawString(font, playerInventoryTitle, inventoryLabelX, inventoryLabelY, 0x404040, false);
     }
 
     @Override public void render(GuiGraphics graphics, int mouseX, int mouseY, float partialTick) {
         super.render(graphics, mouseX, mouseY, partialTick);
         renderTooltip(graphics, mouseX, mouseY);
+        if (!menu.book().isEmpty()) {
+            for (int index = 0; index < FLAGS.length; index++) {
+                if (inside(mouseX, mouseY, 5 + (index / 3) * 20, 10 + (index % 3) * 20, 18, 18)) {
+                    Component label = FLAGS[index] == LinkProperties.DISABLE_PLATFORM
+                            ? Component.literal("Generate Platform: "
+                            + (menu.book().getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE)
+                            .has(LinkProperties.DISABLE_PLATFORM) ? "Off" : "On"))
+                            : LinkProperties.name(FLAGS[index]);
+                    graphics.renderTooltip(font, label, mouseX, mouseY);
+                    return;
+                }
+            }
+        }
+        if (menu.canDelete(minecraft.player)
+                && inside(mouseX, mouseY, menu.awaitingDeletionConfirmation() ? 140 : 120, 32, 18, 18))
+            graphics.renderTooltip(font, Component.translatable(menu.awaitingDeletionConfirmation()
+                    ? "screen.rivencraft.link_modifier.confirm" : "screen.rivencraft.link_modifier.retire"),
+                    mouseX, mouseY);
     }
 }

src/main/java/net/dnorberg/rivencraft/gametest/Milestone7PolishGameTests.java

@@ -14,6 +14,26 @@ import net.neoforged.neoforge.gametest.PrefixGameTestTemplate;
 public final class Milestone7PolishGameTests {
     private Milestone7PolishGameTests() {}
 
+    @GameTest(template = "empty")
+    public static void modifierFlagsKeepLegacyIntraRules(GameTestHelper helper) {
+        LinkProperties linking = new LinkProperties(LinkProperties.DISARM | LinkProperties.INTRA_LINKING
+                | LinkProperties.INTRA_LINKING_ONLY | LinkProperties.RELATIVE_LINK
+                | LinkProperties.DISABLE_PLATFORM);
+        helper.assertTrue(linking.has(LinkProperties.INTRA_LINKING_ONLY)
+                        && linking.has(LinkProperties.RELATIVE_LINK)
+                        && linking.has(LinkProperties.DISABLE_PLATFORM),
+                "The new link options must retain independent flag values");
+        LinkProperties descriptive = linking.forDescriptiveBook();
+        helper.assertTrue(!descriptive.has(LinkProperties.INTRA_LINKING)
+                        && !descriptive.has(LinkProperties.INTRA_LINKING_ONLY),
+                "Intra-only controls must not constrain Descriptive Books");
+        helper.assertTrue(descriptive.has(LinkProperties.DISARM)
+                        && descriptive.has(LinkProperties.RELATIVE_LINK)
+                        && descriptive.has(LinkProperties.DISABLE_PLATFORM),
+                "Shared link options must remain active on Descriptive Books");
+        helper.succeed();
+    }
+
     @GameTest(template = "empty")
     public static void linkSoundPriorityMatchesLegacy(GameTestHelper helper) {
         helper.assertTrue(LinkVisualEffects.sound(LinkProperties.NONE, false) == ModSounds.LINK.get(),

src/main/java/net/dnorberg/rivencraft/item/DescriptiveBookItem.java

@@ -61,7 +61,10 @@ public final class DescriptiveBookItem extends Item {
         }
 
         LinkTarget returnTarget = LinkTarget.from(player);
-        LinkTarget ageTarget = AgeDimensionService.resolve(player, age).orElse(null);
+        LinkProperties properties = stack.getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE)
+                .forDescriptiveBook();
+        LinkTarget ageTarget = AgeDimensionService.resolve(player, age, net.dnorberg.rivencraft.writing.OrderedWriting.EMPTY,
+                !properties.has(LinkProperties.DISABLE_PLATFORM)).orElse(null);
         if (ageTarget == null) {
             player.displayClientMessage(Component.translatable("message.rivencraft.descriptive_book.unavailable"), true);
             return false;
@@ -69,8 +72,6 @@ public final class DescriptiveBookItem extends Item {
 
         ServerLevel sourceLevel = player.serverLevel();
         Vec3 sourcePosition = player.position();
-        LinkProperties properties = stack.getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE)
-                .forDescriptiveBook();
         LinkingService.LinkResult result = portal
                 ? LinkingService.travelDescriptivePortal(player, ageTarget, properties)
                 : hand == null ? LinkingService.travelWithFooting(player, ageTarget, properties)

src/main/java/net/dnorberg/rivencraft/item/LinkingBookItem.java

@@ -79,6 +79,7 @@ public final class LinkingBookItem extends Item {
         String errorKey = switch (result) {
             case MISSING_DIMENSION -> "message.rivencraft.linking_book.missing_dimension";
             case INTRA_LINKING_REQUIRED -> "message.rivencraft.linking_book.intra_required";
+            case INTRA_ONLY -> "message.rivencraft.linking_book.intra_only";
             default -> "message.rivencraft.linking_book.unsafe";
         };
         player.displayClientMessage(Component.translatable(errorKey), true);

src/main/java/net/dnorberg/rivencraft/menu/LinkModifierMenu.java

@@ -29,12 +29,17 @@ public final class LinkModifierMenu extends AbstractContainerMenu {
     public static final int TOGGLE_MOMENTUM = 2;
     public static final int TOGGLE_INTRA = 3;
     public static final int DELETE_AGE = 4;
+    public static final int TOGGLE_INTRA_ONLY = 5;
+    public static final int TOGGLE_RELATIVE = 6;
+    public static final int TOGGLE_PLATFORM = 7;
     private static final int PLAYER_START = 1;
     private static final int MAX_TITLE_LENGTH = 32;
 
     private final LinkModifierBlockEntity modifier;
     private final Container bookSlot;
     private final boolean clientSide;
+    private final Player owner;
+    private final int[] seedWords = new int[4];
     private int confirmation;
     private UUID pendingAge;
 
@@ -48,11 +53,21 @@ public final class LinkModifierMenu extends AbstractContainerMenu {
         this.modifier = modifier;
         this.bookSlot = modifier == null ? new SimpleContainer(1) : modifier;
         this.clientSide = inventory.player.level().isClientSide;
+        this.owner = inventory.player;
         addDataSlot(new DataSlot() {
             @Override public int get() { return confirmation; }
             @Override public void set(int value) { confirmation = value; }
         });
-        addSlot(new Slot(bookSlot, 0, 80, 30) {
+        for (int index = 0; index < seedWords.length; index++) {
+            final int word = index;
+            addDataSlot(new DataSlot() {
+                @Override public int get() {
+                    return clientSide ? seedWords[word] : (int) ((seed() >>> (word * 16)) & 0xffffL);
+                }
+                @Override public void set(int value) { seedWords[word] = value & 0xffff; }
+            });
+        }
+        addSlot(new Slot(bookSlot, 0, 80, 35) {
             @Override public boolean mayPlace(ItemStack stack) { return bookSlot.canPlaceItem(0, stack); }
             @Override public int getMaxStackSize() { return 1; }
             @Override public void setChanged() {
@@ -62,12 +77,45 @@ public final class LinkModifierMenu extends AbstractContainerMenu {
             }
         });
         for (int row = 0; row < 3; row++) for (int col = 0; col < 9; col++)
-            addSlot(new Slot(inventory, col + row * 9 + 9, 8 + col * 18, 112 + row * 18));
+            addSlot(new Slot(inventory, col + row * 9 + 9, 8 + col * 18, 84 + row * 18));
         for (int col = 0; col < 9; col++)
-            addSlot(new Slot(inventory, col, 8 + col * 18, 170));
+            addSlot(new Slot(inventory, col, 8 + col * 18, 142));
     }
 
     public ItemStack book() { return bookSlot.getItem(0); }
+    public boolean hasSeed() {
+        return book().is(ModItems.DESCRIPTIVE_BOOK.get())
+                && book().has(ModDataComponents.AGE_REFERENCE.get());
+    }
+    public long seed() {
+        if (clientSide) {
+            long result = 0;
+            for (int index = 0; index < seedWords.length; index++)
+                result |= (seedWords[index] & 0xffffL) << (index * 16);
+            return result;
+        }
+        if (!hasSeed()) return 0;
+        AgeReference reference = book().get(ModDataComponents.AGE_REFERENCE.get());
+        return AgeRegistrySavedData.get(((ServerPlayer) owner).serverLevel()).find(reference.id())
+                .map(AgeDefinition::seed).orElse(0L);
+    }
+
+    public boolean setSeed(Player player, String text) {
+        if (clientSide || !stillValid(player) || !hasSeed() || text == null || text.length() > 21
+                || !(player instanceof ServerPlayer serverPlayer)) return false;
+        long requested;
+        try { requested = Long.parseLong(text.strip()); }
+        catch (NumberFormatException exception) { return false; }
+        AgeReference reference = book().get(ModDataComponents.AGE_REFERENCE.get());
+        if (reference == null) return false;
+        boolean changed = AgeRegistrySavedData.get(serverPlayer.serverLevel())
+                .reseed(serverPlayer.getServer(), reference.id(), requested);
+        player.displayClientMessage(Component.translatable(changed
+                ? "message.rivencraft.link_modifier.seed_changed"
+                : "message.rivencraft.link_modifier.seed_failed"), false);
+        if (changed) broadcastChanges();
+        return changed;
+    }
     public boolean awaitingDeletionConfirmation() { return confirmation == 1; }
     public boolean canDelete(Player player) {
         return player.hasPermissions(2) && book().is(ModItems.DESCRIPTIVE_BOOK.get())
@@ -92,11 +140,18 @@ public final class LinkModifierMenu extends AbstractContainerMenu {
             case TOGGLE_DISARM -> LinkProperties.DISARM;
             case TOGGLE_MOMENTUM -> LinkProperties.MAINTAIN_MOMENTUM;
             case TOGGLE_INTRA -> LinkProperties.INTRA_LINKING;
+            case TOGGLE_INTRA_ONLY -> LinkProperties.INTRA_LINKING_ONLY;
+            case TOGGLE_RELATIVE -> LinkProperties.RELATIVE_LINK;
+            case TOGGLE_PLATFORM -> LinkProperties.DISABLE_PLATFORM;
             default -> 0;
         };
-        if (flag == 0 || (flag == LinkProperties.INTRA_LINKING
+        if (flag == 0 || ((flag == LinkProperties.INTRA_LINKING || flag == LinkProperties.INTRA_LINKING_ONLY)
                 && book().is(ModItems.DESCRIPTIVE_BOOK.get()))) return false;
         int flags = book().getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE).flags();
+        if (flag == LinkProperties.INTRA_LINKING_ONLY && (flags & LinkProperties.INTRA_LINKING_ONLY) == 0)
+            flags |= LinkProperties.INTRA_LINKING;
+        if (flag == LinkProperties.INTRA_LINKING && (flags & LinkProperties.INTRA_LINKING) != 0)
+            flags &= ~LinkProperties.INTRA_LINKING_ONLY;
         book().set(ModDataComponents.LINK_PROPERTIES.get(), new LinkProperties(flags ^ flag));
         bookSlot.setChanged();
         pendingAge = null;

src/main/java/net/dnorberg/rivencraft/mixin/AgeDimensionSeedMixin.java

@@ -0,0 +1,24 @@
+package net.dnorberg.rivencraft.mixin;
+
+import dev.galacticraft.dynamicdimensions.impl.DynamicDimensionRegistryImpl;
+import net.dnorberg.rivencraft.book.AgeRegistrySavedData;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.dimension.LevelStem;
+import net.minecraft.world.level.storage.WorldData;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.ModifyVariable;
+
+/** Give Dynamic Dimensions the saved Age seed before it constructs the level and its chunk RandomState. */
+@Mixin(value = DynamicDimensionRegistryImpl.class, remap = false)
+public abstract class AgeDimensionSeedMixin {
+    @ModifyVariable(method = "createDynamicLevel(Lnet/minecraft/resources/ResourceKey;Lnet/minecraft/world/level/storage/WorldData;Lnet/minecraft/world/level/dimension/LevelStem;Lnet/minecraft/server/level/ServerLevel;)Lnet/minecraft/server/level/ServerLevel;",
+            at = @At("STORE"), ordinal = 0, remap = false)
+    private long rivencraft$useSavedAgeSeed(long defaultSeed, ResourceKey<Level> dimension,
+                                            WorldData worldData, LevelStem stem, ServerLevel overworld) {
+        return AgeRegistrySavedData.get(overworld).findByDimension(dimension.location())
+                .map(age -> age.seed()).orElse(defaultSeed);
+    }
+}

src/main/java/net/dnorberg/rivencraft/network/ModNetworking.java

@@ -1,6 +1,7 @@
 package net.dnorberg.rivencraft.network;
 
 import net.dnorberg.rivencraft.book.LinkTarget;
+import net.dnorberg.rivencraft.book.LinkProperties;
 import net.dnorberg.rivencraft.book.LinkingService;
 import net.dnorberg.rivencraft.book.AgeReference;
 import net.dnorberg.rivencraft.book.AgeRegistrySavedData;
@@ -60,7 +61,7 @@ public final class ModNetworking {
     }
 
     public static void register(RegisterPayloadHandlersEvent event) {
-        PayloadRegistrar registrar = event.registrar("16");
+        PayloadRegistrar registrar = event.registrar("17");
         registrar.playToServer(RequestDescriptiveBookScreenPayload.TYPE, RequestDescriptiveBookScreenPayload.STREAM_CODEC,
                 ModNetworking::requestDescriptiveBookScreen);
         registrar.playToClient(OpenDescriptiveBookScreenPayload.TYPE, OpenDescriptiveBookScreenPayload.STREAM_CODEC,
@@ -88,6 +89,8 @@ public final class ModNetworking {
                 ModNetworking::setBookBinderTitle);
         registrar.playToServer(SetLinkModifierTitlePayload.TYPE, SetLinkModifierTitlePayload.STREAM_CODEC,
                 ModNetworking::setLinkModifierTitle);
+        registrar.playToServer(SetLinkModifierSeedPayload.TYPE, SetLinkModifierSeedPayload.STREAM_CODEC,
+                ModNetworking::setLinkModifierSeed);
     }
 
     private static void setBookBinderTitle(SetBookBinderTitlePayload payload, IPayloadContext context) {
@@ -106,6 +109,13 @@ public final class ModNetworking {
         }
     }
 
+    private static void setLinkModifierSeed(SetLinkModifierSeedPayload payload, IPayloadContext context) {
+        if (context.player() instanceof ServerPlayer player
+                && player.containerMenu instanceof LinkModifierMenu menu
+                && menu.containerId == payload.containerId())
+            menu.setSeed(player, payload.seed());
+    }
+
     private static void requestDescriptiveBookScreen(RequestDescriptiveBookScreenPayload payload, IPayloadContext context) {
         if (!(context.player() instanceof ServerPlayer player)) {
             return;
@@ -174,7 +184,9 @@ public final class ModNetworking {
         try {
             AgeReference reference = new AgeReference(UUID.randomUUID(), title);
             if (AgeDimensionService.resolve(player, reference, access.stack()
-                    .getOrDefault(ModDataComponents.BOOK_WRITING.get(), OrderedWriting.EMPTY)).isEmpty()) {
+                    .getOrDefault(ModDataComponents.BOOK_WRITING.get(), OrderedWriting.EMPTY),
+                    !access.stack().getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE)
+                            .has(LinkProperties.DISABLE_PLATFORM)).isEmpty()) {
                 player.displayClientMessage(Component.translatable("message.rivencraft.descriptive_book.unavailable"), true);
                 return;
             }
@@ -280,7 +292,9 @@ public final class ModNetworking {
         LinkTarget target;
         if (payload.descriptiveBook() && stack.is(ModItems.DESCRIPTIVE_BOOK.get())) {
             AgeReference age = stack.get(ModDataComponents.AGE_REFERENCE.get());
-            target = age == null ? null : AgeDimensionService.resolve(player, age).orElse(null);
+            target = age == null ? null : AgeDimensionService.resolve(player, age, OrderedWriting.EMPTY,
+                    !stack.getOrDefault(ModDataComponents.LINK_PROPERTIES.get(), LinkProperties.NONE)
+                            .has(LinkProperties.DISABLE_PLATFORM)).orElse(null);
         } else if (!payload.descriptiveBook() && stack.is(ModItems.LINKING_BOOK.get())) {
             target = stack.get(ModDataComponents.LINK_TARGET.get());
         } else {

src/main/java/net/dnorberg/rivencraft/network/SetLinkModifierSeedPayload.java

@@ -0,0 +1,19 @@
+package net.dnorberg.rivencraft.network;
+
+import net.dnorberg.rivencraft.Rivencraft;
+import net.minecraft.network.RegistryFriendlyByteBuf;
+import net.minecraft.network.codec.ByteBufCodecs;
+import net.minecraft.network.codec.StreamCodec;
+import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.ResourceLocation;
+
+public record SetLinkModifierSeedPayload(int containerId, String seed) implements CustomPacketPayload {
+    public static final Type<SetLinkModifierSeedPayload> TYPE = new Type<>(
+            ResourceLocation.fromNamespaceAndPath(Rivencraft.MOD_ID, "set_link_modifier_seed"));
+    public static final StreamCodec<RegistryFriendlyByteBuf, SetLinkModifierSeedPayload> STREAM_CODEC =
+            StreamCodec.composite(ByteBufCodecs.VAR_INT, SetLinkModifierSeedPayload::containerId,
+                    ByteBufCodecs.STRING_UTF8, SetLinkModifierSeedPayload::seed,
+                    SetLinkModifierSeedPayload::new);
+
+    @Override public Type<? extends CustomPacketPayload> type() { return TYPE; }
+}

src/main/resources/assets/rivencraft/lang/en_us.json

@@ -15,6 +15,9 @@
   "item.rivencraft.link_property.disarm": "Disarm",
   "item.rivencraft.link_property.maintain_momentum": "Maintain Momentum",
   "item.rivencraft.link_property.intra_linking": "Intra Linking",
+  "item.rivencraft.link_property.intra_linking_only": "Intra-Linking Only",
+  "item.rivencraft.link_property.relative_link": "Relative Link",
+  "item.rivencraft.link_property.disable_platform": "Generate Platform: Off",
   "item.rivencraft.page.unresolved": "Unresolved Symbol Page",
   "item.rivencraft.notebook": "Notebook",
   "item.rivencraft.collation_folder": "Collation Folder",
@@ -22,6 +25,10 @@
   "block.rivencraft.link_modifier": "Link Modifier",
   "container.rivencraft.link_modifier": "Link Modifier",
   "screen.rivencraft.link_modifier.title": "Book title",
+  "screen.rivencraft.link_modifier.seed": "Age seed",
+  "screen.rivencraft.link_modifier.seed_warning": "Changing the seed preserves existing chunks but changes newly generated terrain. Press Enter to apply. The Age must be empty.",
+  "message.rivencraft.link_modifier.seed_changed": "Age seed changed. Existing chunks remain; newly generated chunks use the new seed.",
+  "message.rivencraft.link_modifier.seed_failed": "Could not change seed. Use a signed whole number and ensure no players are in the Age.",
   "screen.rivencraft.link_modifier.retire": "Retire Age",
   "screen.rivencraft.link_modifier.confirm": "Confirm!",
   "message.rivencraft.link_modifier.delete.retired": "Age retired. Its terrain was archived outside the active world.",
@@ -100,6 +107,7 @@
   "message.rivencraft.linking_book.missing_dimension": "That dimension is unavailable",
   "message.rivencraft.linking_book.unsafe": "No safe destination was found near the link",
   "message.rivencraft.linking_book.intra_required": "This book needs an Intra Linking panel for same-dimension travel",
+  "message.rivencraft.linking_book.intra_only": "This book can only link within its current dimension",
   "message.rivencraft.descriptive_book.unwritten": "This Descriptive Book is unwritten",
   "message.rivencraft.descriptive_book.created": "Created Age: %s",
   "message.rivencraft.descriptive_book.unavailable": "That Age is unavailable",

src/main/resources/rivencraft.mixins.json

@@ -4,6 +4,7 @@
   "package": "net.dnorberg.rivencraft.mixin",
   "compatibilityLevel": "JAVA_21",
   "mixins": [
+    "AgeDimensionSeedMixin",
     "AgeDungeonPlacementMixin",
     "AgeStructureBiomeMixin",
     "StructurePlacementAccessor"