Port Legacy-style Star Fissures age feature (#58)

docs/ASSET_PROVENANCE.md

@@ -28,6 +28,7 @@ project's GNU LGPL v3 license. Rivencraft itself uses the same license.
 | `assets/rivencraft/textures/block/crystal_block.png`, `budding_crystal.png` | `assets/mystcraft/textures/blocks/crystal.png` | Legacy 0.13.7.06 local extraction | Exact 16×16 blue tile reused for both solid crystal blocks |
 | `assets/rivencraft/textures/block/{small,medium,large}_crystal_bud.png`, `crystal_cluster.png` | Minecraft 1.21.1 `textures/block/{small,medium,large}_amethyst_bud.png`, `amethyst_cluster.png` | Minecraft 1.21.1 | Original 16×16 alpha masks and silhouettes preserved; hue shifted toward Legacy blue, with brighter saturation; exported as 8-bit RGBA (not indexed PNG) |
 | `assets/rivencraft/textures/item/crystal_shard.png` | Original sprite generated with OpenAI ImageGen from the Legacy crystal palette | 2026-10-05 | Cropped and nearest-neighbor scaled to 16×16 |
+| `assets/rivencraft/sounds/linking/link-fissure.ogg` | `assets/mystcraft/sounds/linking/link-fissure.ogg` | Legacy 0.13.7.06 local extraction | Namespace/path rename only; plays when a Star Fissure returns an entity home |
 
 Mystcraft Legacy identifies XCompWiz as its project developer and includes the
 full LGPL v3 text in its root `LICENSE` file. Rivencraft's root `LICENSE`

docs/LEGACY_AGE_GRAMMAR_AUDIT.md

@@ -18,7 +18,7 @@ Legacy does **not** reject a book just because it omits terrain, biome, weather,
 | `WeatherNorm`, `Fast`, `Slow`, `Off`, `On`, `Cloudy`, `Rain`, `Snow`, `Storm` | `AgeTraits.Weather` has matching names except Legacy `On` maps to `ALWAYS` | Compile weather semantics separately from biome selection. `Snow` must remain deferred until optional season integration; do not silently substitute another weather mode. |
 | Suns, moons, starfields; angle, phase, period, color/gradient/sunset modifiers | One `celestialPeriod`, `celestialAngle`, `celestialPhase` on `AgeTraits` | Compile only the representable single-cycle subset first. Multiple celestial bodies, independent periods, custom stars, gradients and sunsets need a richer definition and renderer, not flattening into one value. |
 | Sky/fog/cloud/grass/foliage/water colors, natural variants, horizon, rainbow | Existing sky/dimension visuals and preview | Require an explicit modern client/biome-color design; metadata-only symbol pages must not pretend to change rendering. |
-| Caves, ores, huge trees, lakes, floating islands, tendrils, skylands, spheres, spikes, crystals; vanilla villages, strongholds, mineshafts, dungeons, fortresses, obelisks, fissures | Current cave profile, authored Floating Islands/Tendrils/Skylands/Spheres/Spikes/Obelisks/Crystal Formations and Dense Ores, and page-gated vanilla Dungeons/Mineshafts/Nether Fortresses/Strongholds/Villages | The five Legacy vanilla structure symbols gate Minecraft 1.21.1 generation. Dungeons use monster-room placement; the others use vanilla structure sets. Obelisks use a bespoke 4×4 plinth and 2×12×2 shaft with safe modern placement. Crystal Formations retain Legacy's blue tile and one-in-fifteen attempt rate but use new budding, shard-producing mounds. Fissures and exact 1.12 structure geometry remain separate work. |
+| Caves, ores, huge trees, lakes, floating islands, tendrils, skylands, spheres, spikes, crystals; vanilla villages, strongholds, mineshafts, dungeons, fortresses, obelisks, fissures | Current cave profile, authored Floating Islands/Tendrils/Skylands/Spheres/Spikes/Obelisks/Crystal Formations/Star Fissures and Dense Ores, and page-gated vanilla Dungeons/Mineshafts/Nether Fortresses/Strongholds/Villages | The five Legacy vanilla structure symbols gate Minecraft 1.21.1 generation. Dungeons use monster-room placement; the others use vanilla structure sets. Obelisks use a bespoke 4×4 plinth and 2×12×2 shaft with safe modern placement. Crystal Formations retain Legacy's blue tile and one-in-fifteen attempt rate but use new budding, shard-producing mounds. Star Fissures reproduce Legacy's spawn-chunk footprint, open-to-sky columns, home link, and sound. Their renderer uses the modern End Portal pipeline in place of Legacy's retired fixed-function OpenGL calls. Exact 1.12 geometry for other structures remains separate work. |
 | `EnvAccel`, explosions, lightning, meteors, scorching; PvP and dummy suppression pages | No equivalent Age-definition effect | Defer environmental hazards/instability effects to milestone 6, PvP rule to a separately scoped server policy; retain authored IDs without fake behavior. |
 
 The Legacy symbol list and page names come from [ModSymbols](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/data/ModSymbols.java#L129-L240) and [SymbolRules](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/data/SymbolRules.java#L19-L137). Rivencraft's [catalog](../src/main/java/net/dnorberg/rivencraft/writing/SymbolCatalog.java) currently holds display metadata only; its built-in set is just standard terrain, native biomes, normal weather, normal lighting, normal time, and caves. [OrderedWriting](../src/main/java/net/dnorberg/rivencraft/writing/OrderedWriting.java) preserves page order, but no compiler yet connects it to [AgeTraits](../src/main/java/net/dnorberg/rivencraft/book/AgeTraits.java) or [Age profiles](AGE_PROFILES.md).

docs/WRITING_GRAMMAR.md

@@ -20,4 +20,6 @@ Material pages are generated for registered full-collision, non-fluid blocks and
 
 Crystal Formations are an authored, material-free feature on exposed solid terrain, including Flat terrain; Cave and Void reject the page. Like Legacy, one in fifteen eligible chunks attempts a formation, with the site fixed by the Age seed and chunk coordinates. The modern formation is a compact mound with budding hearts instead of Legacy's long crystal lines. Budding blocks grow through small, medium, and large buds into clusters using vanilla amethyst timing and sounds. Non-silk cluster harvest yields Crystal Shards; four shards craft one Crystal Block. These blocks and shards use 16×16 textures: Legacy's crystal tile for solids and hue-shifted vanilla amethyst sprites for buds and clusters. A page-free Age can also randomly select Crystal Formations; an authored page always retains its exact choice in the saved plan.
 
+Star Fissures are a material-free feature on every terrain profile, including Cave and Void. The fissure is generated once beside the first resolved spawn, using Legacy's spawn-chunk offset and 10–17 paired, irregular X-span rows running along +Z. Each portal tile is placed at y=0 and its column is opened to the sky, as in Legacy. For modern terrain with a surface below y=0, the portal uses the minimum build height plus one instead; empty Void columns keep y=0. Its non-solid portal links to the Overworld spawn with the Legacy fissure sound; the animated starfield is drawn with Minecraft's current End Portal renderer, which uses the same end-sky/end-portal art as Legacy's custom renderer. Random Ages sample Legacy's default small-feature grammar for fissure selection: the stop/one/repeat branches have rank-derived weights 1:1:3, and the fissure has weight 1 of 9 among its small-feature rules. The remainder of random feature selection still follows Rivencraft's current pipeline, rather than running Legacy's entire Age grammar.
+
 The Rivencraft symbol-page creative tabs read a generated index of bundled symbol definitions and group Pages by each definition's category, except biome-controller roles, which appear in a separate Biome Generation tab rather than the Biome tab. Adding another valid JSON symbol under `src/main/resources/data/rivencraft/rivencraft/symbols/` includes its page in the matching category tab on the next build; a new bundled category receives its own tab. Registry-derived Block and Fluid Pages have separate tabs and both appear in optional JEI. Link Pages have a separate tab. Blank Pages appear in neither the creative tabs nor JEI's ingredient list. The server catalog still decides whether a page is valid for writing. External server data-pack symbols are not included in this bundled index.

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=0.4.18.2
+mod_version=0.4.19.1
 immersive_portals_version=6.0.7
 terrablender_version=4.1.0.8
 serene_seasons_version_id=B6nTjh4b

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

@@ -0,0 +1,84 @@
+package net.dnorberg.rivencraft.block;
+
+import com.mojang.serialization.MapCodec;
+import net.dnorberg.rivencraft.block.entity.StarFissureBlockEntity;
+import net.dnorberg.rivencraft.book.LinkingService;
+import net.dnorberg.rivencraft.registry.ModSounds;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.sounds.SoundSource;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.level.BlockGetter;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.LevelReader;
+import net.minecraft.world.level.block.BaseEntityBlock;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Portal;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.state.BlockBehaviour;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.material.Fluid;
+import net.minecraft.world.level.portal.DimensionTransition;
+import net.minecraft.world.phys.Vec3;
+import net.minecraft.world.phys.shapes.BooleanOp;
+import net.minecraft.world.phys.shapes.CollisionContext;
+import net.minecraft.world.phys.shapes.Shapes;
+import net.minecraft.world.phys.shapes.VoxelShape;
+
+/** A starry, non-obtainable portal at the base of a generated fissure. */
+public final class StarFissureBlock extends BaseEntityBlock implements Portal {
+    public static final MapCodec<StarFissureBlock> CODEC = simpleCodec(StarFissureBlock::new);
+    private static final VoxelShape SHAPE = Block.box(0, 0, 0, 16, 1.6, 16);
+
+    public StarFissureBlock(BlockBehaviour.Properties properties) {
+        super(properties);
+    }
+
+    @Override
+    protected MapCodec<? extends BaseEntityBlock> codec() {
+        return CODEC;
+    }
+
+    @Override
+    public BlockEntity newBlockEntity(BlockPos pos, BlockState state) {
+        return new StarFissureBlockEntity(pos, state);
+    }
+
+    @Override
+    protected VoxelShape getShape(BlockState state, BlockGetter level, BlockPos pos, CollisionContext context) {
+        return SHAPE;
+    }
+
+    @Override
+    protected void entityInside(BlockState state, Level level, BlockPos pos, Entity entity) {
+        if (entity.canUsePortal(false) && Shapes.joinIsNotEmpty(
+                Shapes.create(entity.getBoundingBox().move(-pos.getX(), -pos.getY(), -pos.getZ())),
+                state.getShape(level, pos), BooleanOp.AND)) {
+            entity.setAsInsidePortal(this, pos);
+        }
+    }
+
+    @Override
+    public DimensionTransition getPortalDestination(ServerLevel level, Entity entity, BlockPos pos) {
+        if (level.dimension() == Level.OVERWORLD) return null;
+        ServerLevel overworld = level.getServer().overworld();
+        if (overworld == null) return null;
+        Vec3 destination = LinkingService.resolveDestination(overworld, overworld.getSharedSpawnPos(), true)
+                .orElse(overworld.getSharedSpawnPos().getBottomCenter());
+        level.playSound(null, pos, ModSounds.LINK_FISSURE.get(), SoundSource.BLOCKS, 1.0F, 1.0F);
+        return new DimensionTransition(overworld, destination,
+                entity.getDeltaMovement(), entity.getYRot(), entity.getXRot(),
+                DimensionTransition.PLACE_PORTAL_TICKET);
+    }
+
+    @Override
+    public ItemStack getCloneItemStack(LevelReader level, BlockPos pos, BlockState state) {
+        return ItemStack.EMPTY;
+    }
+
+    @Override
+    protected boolean canBeReplaced(BlockState state, Fluid fluid) {
+        return false;
+    }
+}

src/main/java/net/dnorberg/rivencraft/block/entity/StarFissureBlockEntity.java

@@ -0,0 +1,13 @@
+package net.dnorberg.rivencraft.block.entity;
+
+import net.dnorberg.rivencraft.registry.ModBlockEntities;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.level.block.entity.TheEndPortalBlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+
+/** Reuses Minecraft's animated starfield renderer with a valid Rivencraft block-entity type. */
+public final class StarFissureBlockEntity extends TheEndPortalBlockEntity {
+    public StarFissureBlockEntity(BlockPos pos, BlockState state) {
+        super(ModBlockEntities.STAR_FISSURE.get(), pos, state);
+    }
+}

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

@@ -39,6 +39,7 @@ import net.minecraft.world.level.biome.MultiNoiseBiomeSource;
 import net.dnorberg.rivencraft.world.ScaledBiomeSource;
 import net.dnorberg.rivencraft.world.AgeFlatChunkGenerator;
 import net.dnorberg.rivencraft.world.AgeFeatureChunkGenerator;
+import net.dnorberg.rivencraft.world.StarFissureFeature;
 import net.minecraft.world.level.chunk.ChunkGenerator;
 import net.minecraft.world.level.dimension.BuiltinDimensionTypes;
 import net.minecraft.world.level.dimension.DimensionType;
@@ -98,6 +99,12 @@ public final class AgeDimensionService {
         if (spawn == null) {
             applyInitialCelestialPhase(level, definition);
             spawn = createSafeSpawn(level, definition);
+            if (AgeFeatureSelection.resolved(definition.plan()).stream()
+                    .anyMatch(choice -> choice.id().equals(AgeFeatureSelection.STAR_FISSURES))
+                    || definition.randomFeatures().stream()
+                    .anyMatch(choice -> choice.id().equals(AgeFeatureSelection.STAR_FISSURES))) {
+                StarFissureFeature.generate(level, definition.seed(), spawn);
+            }
             definition = AgeRegistrySavedData.get(level).setSpawn(definition.id(), spawn);
         }
         return Optional.of(new LinkTarget(

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

@@ -32,7 +32,9 @@ public final class AgeFeatureSelection {
     private static final List<ResourceLocation> FLUID_FEATURES = List.of(
             id("surface_lakes"), id("deep_lakes"), id("lava_lakes"));
     private static final long RANDOM_SKYLANDS_SALT = 0x534B594C414E4453L;
+    private static final long RANDOM_STAR_FISSURES_SALT = 0x535441524752414DL;
     public static final ResourceLocation CRYSTAL_FORMATIONS = id("crystal_formations");
+    public static final ResourceLocation STAR_FISSURES = id("star_fissures");
 
     private AgeFeatureSelection() {}
 
@@ -176,12 +178,33 @@ public final class AgeFeatureSelection {
             choices.add(new Choice(id("skylands"), Optional.empty()));
         if (error(CRYSTAL_FORMATIONS, profile, registries) == null && random.nextInt(10) == 0)
             choices.add(new Choice(CRYSTAL_FORMATIONS, Optional.empty()));
+        if (randomStarFissure(ageSeed))
+            choices.add(new Choice(STAR_FISSURES, Optional.empty()));
         AgeBiomeSelection biomes = AgeBiomeSelection.compile(WritingGrammar.parse(OrderedWriting.EMPTY),
                 AgeTraits.select(ageSeed), profile, ageSeed, registries);
         choices.addAll(AgeStructureSelection.randomChoices(ageSeed, profile, biomes, registries));
         return List.copyOf(choices);
     }
 
+    /**
+     * Legacy's default FeatureSmalls0 grammar: stop without a feature (rank 4),
+     * emit one (rank 4), or emit one and repeat (rank 2). Its rank-derived
+     * weights are 1:1:3. Within FEATURE_SMALL, the Star Fissure rule has weight
+     * 1 of 9: three rank-3 choices have weight 1 each and two rank-1 lake
+     * choices have weight 3 each. Other small features remain selected by this
+     * port's existing random feature pipeline; only the fissure result is used.
+     */
+    private static boolean randomStarFissure(long ageSeed) {
+        Random random = new Random(mix(ageSeed ^ RANDOM_STAR_FISSURES_SALT));
+        for (int step = 0; step < 27; step++) {
+            int branch = random.nextInt(5);
+            if (branch == 0) return false;
+            if (random.nextInt(9) == 0) return true;
+            if (branch == 1) return false;
+        }
+        return false;
+    }
+
     private static List<ResourceLocation> shuffledMaterials(long ageSeed, ResourceLocation feature) {
         var category = solidFeature(feature)
                 ? BlockSymbolPages.CATEGORY : BlockSymbolPages.FLUID_CATEGORY;
@@ -212,6 +235,7 @@ public final class AgeFeatureSelection {
                 return "Feature " + choice + " needs exposed solid ground, not Cave or Void terrain";
             return null;
         }
+        if (choice.equals(STAR_FISSURES)) return null;
         if (skylands(choice)) return null;
         if (tendrils(choice)) return null;
         if (spheres(choice)) return null;

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

@@ -79,11 +79,13 @@ public final class AgePersistenceGameTests {
                     "A random Age may roll at most two distinct structure features");
             for (AgeFeatureSelection.Choice choice : age.randomFeatures()) {
                 helper.assertTrue(AgeFeatureSelection.skylands(choice.id())
+                                || choice.id().equals(AgeFeatureSelection.CRYSTAL_FORMATIONS)
+                                || choice.id().equals(AgeFeatureSelection.STAR_FISSURES)
                                 || AgeStructureSelection.feature(choice.id())
                                 ? choice.material().isEmpty()
                                 : choice.material().isPresent()
                                 && AgeFeatureSelection.materialError(choice) == null,
-                        "Random material features need valid blocks or fluids; Skylands and structures need none");
+                        "Random material features need valid blocks or fluids; material-free features need none");
             }
         }
         AgeRegistrySavedData registry = AgeRegistrySavedData.get(helper.getLevel());

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

@@ -40,7 +40,8 @@ public final class FeatureWritingGameTests {
                 "feature/bastions", "feature/buried_treasure", "feature/shipwrecks",
                 "feature/ocean_ruins", "feature/pillager_outposts", "feature/ruined_portals",
                 "feature/nether_fossils", "feature/ancient_cities", "feature/trail_ruins",
-                "feature/dense_ores", "feature/obelisks", "feature/crystal_formations");
+                "feature/dense_ores", "feature/obelisks", "feature/crystal_formations",
+                "feature/star_fissures");
         helper.assertTrue(PageItem.bundledCreativeSymbols().containsAll(pages),
                 "Supported feature pages must appear in the creative and JEI symbol feed");
         for (String path : pages) {
@@ -74,6 +75,7 @@ public final class FeatureWritingGameTests {
                     || AgeFeatureSelection.spikes(choice.id())
                     || AgeFeatureSelection.obelisks(choice.id())
                     || choice.id().equals(AgeFeatureSelection.CRYSTAL_FORMATIONS)
+                    || choice.id().equals(AgeFeatureSelection.STAR_FISSURES)
                     || choice.id().equals(AgeDenseOres.ID)) continue;
             var placement = AgeFeatureSelection.placedFeature(choice.id());
             helper.assertTrue(registries.lookupOrThrow(Registries.PLACED_FEATURE)
@@ -187,8 +189,9 @@ public final class FeatureWritingGameTests {
             helper.assertTrue(random.stream().allMatch(choice -> AgeFeatureSelection.tendrils(choice.id())
                             || AgeFeatureSelection.spheres(choice.id())
                             || AgeFeatureSelection.skylands(choice.id())
+                            || choice.id().equals(AgeFeatureSelection.STAR_FISSURES)
                             || AgeStructureSelection.feature(choice.id())),
-                    "Cave random Ages must not choose incompatible surface features");
+                    "Cave random Ages must only choose compatible features, including Star Fissures");
             if (random.stream().anyMatch(choice -> AgeFeatureSelection.tendrils(choice.id()))) found = true;
         }
         helper.assertTrue(found, "A page-free random Cave Age must be able to roll Tendrils");

src/main/java/net/dnorberg/rivencraft/client/ClientEvents.java

@@ -35,6 +35,7 @@ public final class ClientEvents {
     public static void registerRenderers(EntityRenderersEvent.RegisterRenderers event) {
         event.registerBlockEntityRenderer(ModBlockEntities.BOOK_STAND.get(), BookStandRenderer::new);
         event.registerBlockEntityRenderer(ModBlockEntities.WRITING_DESK.get(), WritingDeskRenderer::new);
+        event.registerBlockEntityRenderer(ModBlockEntities.STAR_FISSURE.get(), StarFissureRenderer::new);
     }
 
     @SubscribeEvent

src/main/java/net/dnorberg/rivencraft/client/StarFissureRenderer.java

@@ -0,0 +1,22 @@
+package net.dnorberg.rivencraft.client;
+
+import net.dnorberg.rivencraft.block.entity.StarFissureBlockEntity;
+import net.minecraft.client.renderer.blockentity.BlockEntityRendererProvider;
+import net.minecraft.client.renderer.blockentity.TheEndPortalRenderer;
+
+/** Uses the modern end-portal starfield shader at Legacy's full-block face positions. */
+public final class StarFissureRenderer extends TheEndPortalRenderer<StarFissureBlockEntity> {
+    public StarFissureRenderer(BlockEntityRendererProvider.Context context) {
+        super(context);
+    }
+
+    @Override
+    protected float getOffsetUp() {
+        return 0.0F;
+    }
+
+    @Override
+    protected float getOffsetDown() {
+        return 1.0F;
+    }
+}

src/main/java/net/dnorberg/rivencraft/registry/ModBlockEntities.java

@@ -5,6 +5,7 @@ import net.dnorberg.rivencraft.block.entity.BookStandBlockEntity;
 import net.dnorberg.rivencraft.block.entity.BookBinderBlockEntity;
 import net.dnorberg.rivencraft.block.entity.WritingDeskBlockEntity;
 import net.dnorberg.rivencraft.block.entity.InkMixerBlockEntity;
+import net.dnorberg.rivencraft.block.entity.StarFissureBlockEntity;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.neoforged.bus.api.IEventBus;
@@ -28,6 +29,9 @@ public final class ModBlockEntities {
     public static final DeferredHolder<BlockEntityType<?>, BlockEntityType<InkMixerBlockEntity>> INK_MIXER =
             BLOCK_ENTITIES.register("ink_mixer", () -> BlockEntityType.Builder
                     .of(InkMixerBlockEntity::new, ModBlocks.INK_MIXER.get()).build(null));
+    public static final DeferredHolder<BlockEntityType<?>, BlockEntityType<StarFissureBlockEntity>> STAR_FISSURE =
+            BLOCK_ENTITIES.register("star_fissure", () -> BlockEntityType.Builder
+                    .of(StarFissureBlockEntity::new, ModBlocks.STAR_FISSURE.get()).build(null));
 
     private ModBlockEntities() {
     }

src/main/java/net/dnorberg/rivencraft/registry/ModBlocks.java

@@ -6,6 +6,7 @@ import net.dnorberg.rivencraft.block.BookBinderBlock;
 import net.dnorberg.rivencraft.block.WritingDeskBlock;
 import net.dnorberg.rivencraft.block.InkMixerBlock;
 import net.dnorberg.rivencraft.block.BuddingCrystalBlock;
+import net.dnorberg.rivencraft.block.StarFissureBlock;
 import net.minecraft.world.level.block.AmethystClusterBlock;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.block.Blocks;
@@ -52,6 +53,9 @@ public final class ModBlocks {
     public static final DeferredBlock<AmethystClusterBlock> SMALL_CRYSTAL_BUD = BLOCKS.registerBlock("small_crystal_bud",
             properties -> new AmethystClusterBlock(3.0F, 4.0F, properties),
             BlockBehaviour.Properties.ofFullCopy(Blocks.SMALL_AMETHYST_BUD));
+    public static final DeferredBlock<StarFissureBlock> STAR_FISSURE = BLOCKS.registerBlock("star_fissure",
+            StarFissureBlock::new, BlockBehaviour.Properties.ofFullCopy(Blocks.END_PORTAL)
+                    .lightLevel(state -> 6));
 
     private ModBlocks() {
     }

src/main/java/net/dnorberg/rivencraft/registry/ModSounds.java

@@ -14,6 +14,7 @@ public final class ModSounds {
             DeferredRegister.create(Registries.SOUND_EVENT, Rivencraft.MOD_ID);
 
     public static final DeferredHolder<SoundEvent, SoundEvent> LINK = register("linking.link");
+    public static final DeferredHolder<SoundEvent, SoundEvent> LINK_FISSURE = register("linking.link-fissure");
 
     private ModSounds() {
     }

src/main/java/net/dnorberg/rivencraft/world/StarFissureFeature.java

@@ -0,0 +1,77 @@
+package net.dnorberg.rivencraft.world;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+import net.dnorberg.rivencraft.registry.ModBlocks;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.levelgen.Heightmap;
+
+/**
+ * Ports the footprint and carving of Mystcraft's WorldGenMystStarFissure.
+ * The original is LGPL-3.0, copyright XCompWiz and Mystcraft contributors.
+ */
+public final class StarFissureFeature {
+    private static final long SALT = 0x5354415246495353L;
+
+    private StarFissureFeature() {}
+
+    /** Legacy chooses a point 8–23 blocks inside/after the spawn chunk, then grows the rift along +Z. */
+    public static List<BlockPos> footprint(long ageSeed, BlockPos spawn) {
+        long chunkX = spawn.getX() >> 4;
+        long chunkZ = spawn.getZ() >> 4;
+        Random random = new Random(ageSeed ^ SALT ^ chunkX ^ (chunkZ << 32));
+        int originX = ((int) chunkX << 4) + random.nextInt(16) + 8;
+        int originZ = ((int) chunkZ << 4) + random.nextInt(16) + 8;
+        int length = random.nextInt(8) + 10;
+        int[][] intervals = new int[length][2];
+        List<BlockPos> columns = new ArrayList<>();
+        addRow(columns, originX, originZ, 0, 0, 0);
+        for (int row = 1; row < length; row++) {
+            int range = length + Math.min(row, length - row) + 1;
+            int right = (random.nextInt(range) - (range >> 1) + intervals[row - 1][1]) / 2;
+            int left = (random.nextInt(range) - (range >> 1) + intervals[row - 1][0]) / 2;
+            if (left > right) {
+                int swap = left;
+                left = right;
+                right = swap;
+            }
+            left = Math.min(left, intervals[row - 1][1]);
+            right = Math.max(right, intervals[row - 1][0]);
+            intervals[row][0] = left;
+            intervals[row][1] = right;
+            addRow(columns, originX, originZ, row, left, right);
+        }
+        return List.copyOf(columns);
+    }
+
+    private static void addRow(List<BlockPos> columns, int originX, int originZ, int row, int left, int right) {
+        for (int x = left; x <= right; x++) {
+            columns.add(new BlockPos(originX + x, 0, originZ + row * 2));
+            columns.add(new BlockPos(originX + x, 0, originZ + row * 2 + 1));
+        }
+    }
+
+    public static void generate(ServerLevel level, long ageSeed, BlockPos spawn) {
+        List<BlockPos> columns = footprint(ageSeed, spawn);
+        BlockPos first = columns.getFirst();
+        // 1.12 worlds began at y=0. Modern superflat can sit below it, so use the
+        // modern world floor there. Empty Void columns keep Legacy's y=0 portal.
+        int surface = level.getHeight(Heightmap.Types.WORLD_SURFACE, first.getX(), first.getZ());
+        int minY = level.getMinBuildHeight();
+        int floorY = surface > minY && surface <= 0 ? minY + 1 : Math.max(0, minY + 1);
+        BlockPos.MutableBlockPos mutable = new BlockPos.MutableBlockPos();
+        for (BlockPos column : columns) {
+            int top = level.getHeight(Heightmap.Types.WORLD_SURFACE, column.getX(), column.getZ());
+            level.setBlock(mutable.set(column.getX(), floorY, column.getZ()),
+                    ModBlocks.STAR_FISSURE.get().defaultBlockState(), 2);
+            // Legacy clears all blocks above each portal tile to the sky. Heightmap
+            // bounds the same work without iterating already-empty world height.
+            for (int y = floorY + 1; y < top; y++) {
+                level.setBlock(mutable.set(column.getX(), y, column.getZ()), Blocks.AIR.defaultBlockState(), 2);
+            }
+        }
+    }
+}

src/main/java/net/dnorberg/rivencraft/world/StarFissureGameTests.java

@@ -0,0 +1,103 @@
+package net.dnorberg.rivencraft.world;
+
+import java.util.List;
+import net.dnorberg.rivencraft.Rivencraft;
+import net.dnorberg.rivencraft.book.AgeFeatureSelection;
+import net.dnorberg.rivencraft.book.AgeGenerationPlan;
+import net.dnorberg.rivencraft.book.AgeGenerationProfiles;
+import net.dnorberg.rivencraft.book.AgeRuntimeProfiles;
+import net.dnorberg.rivencraft.book.AgeTraits;
+import net.dnorberg.rivencraft.item.PageItem;
+import net.dnorberg.rivencraft.registry.ModBlocks;
+import net.dnorberg.rivencraft.writing.OrderedWriting;
+import net.dnorberg.rivencraft.writing.SymbolReference;
+import net.dnorberg.rivencraft.writing.WritingEntry;
+import net.minecraft.core.BlockPos;
+import net.minecraft.gametest.framework.GameTest;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.ResourceLocation;
+import net.neoforged.neoforge.gametest.GameTestHolder;
+import net.neoforged.neoforge.gametest.PrefixGameTestTemplate;
+
+/** Pure selection and footprint checks; runtime carving is left to the in-game visual check. */
+@GameTestHolder(Rivencraft.MOD_ID)
+@PrefixGameTestTemplate(false)
+public final class StarFissureGameTests {
+    private StarFissureGameTests() {}
+
+    @GameTest(template = "empty")
+    public static void authoredFissureIsWritableAndSaved(GameTestHelper helper) {
+        var registries = helper.getLevel().registryAccess();
+        helper.assertTrue(PageItem.bundledCreativeSymbols().contains("feature/star_fissures"),
+                "Star Fissures must appear in the creative and JEI page feed");
+        helper.assertTrue(PageItem.isUsableWriting(PageItem.createBundledCreativePage("feature/star_fissures")),
+                "The page must be usable in an authored book");
+        OrderedWriting writing = new OrderedWriting(List.of(WritingEntry.linkPanel(),
+                page("terrain/standard"), page("feature/star_fissures")));
+        AgeGenerationPlan plan = AgeGenerationPlan.compile(writing, 58L, AgeGenerationProfiles.STANDARD,
+                AgeTraits.select(58L), registries);
+        var resolved = AgeFeatureSelection.resolved(plan);
+        helper.assertValueEqual(resolved.size(), 1, "One authored fissure must remain one feature choice");
+        helper.assertValueEqual(resolved.getFirst().id(), AgeFeatureSelection.STAR_FISSURES,
+                "The authored feature must be a Star Fissure");
+        helper.assertTrue(resolved.getFirst().material().isEmpty(), "Star Fissures consume no material page");
+        helper.assertValueEqual(AgeFeatureSelection.resolved(AgeGenerationPlan.load(plan.save())), resolved,
+                "The feature must survive Age-plan save and load");
+        helper.assertTrue(ModBlocks.STAR_FISSURE.get().defaultBlockState() != null,
+                "The non-obtainable star portal block must be registered");
+        for (String terrain : List.of("standard", "amplified", "island", "flat", "cave", "void"))
+            helper.assertTrue(AgeFeatureSelection.error(AgeFeatureSelection.STAR_FISSURES,
+                            AgeRuntimeProfiles.resolve(id(terrain)), registries) == null,
+                    "Legacy fissures can appear on " + terrain + " terrain");
+        helper.succeed();
+    }
+
+    @GameTest(template = "empty")
+    public static void randomFissuresAndSpawnFootprintAreStable(GameTestHelper helper) {
+        var registries = helper.getLevel().registryAccess();
+        int selected = 0;
+        for (long seed = 0; seed < 128; seed++) {
+            boolean standard = hasRandomFissure(seed, AgeGenerationProfiles.STANDARD, registries);
+            if (standard) selected++;
+            for (String terrain : List.of("cave", "void"))
+                helper.assertValueEqual(hasRandomFissure(seed, id(terrain), registries), standard,
+                        "Legacy small-feature selection must not depend on terrain");
+        }
+        helper.assertTrue(selected > 0 && selected < 128,
+                "The weighted Legacy grammar should select fissures in some, not all, random Ages");
+        BlockPos spawn = new BlockPos(0, 64, 0);
+        var footprint = StarFissureFeature.footprint(58L, spawn);
+        helper.assertValueEqual(footprint, StarFissureFeature.footprint(58L, spawn),
+                "The Age seed and spawn must reproduce the same fissure");
+        int minZ = footprint.stream().mapToInt(BlockPos::getZ).min().orElseThrow();
+        int maxZ = footprint.stream().mapToInt(BlockPos::getZ).max().orElseThrow();
+        helper.assertTrue(minZ >= 8 && minZ <= 23,
+                "Legacy starts 8–23 blocks past the spawn chunk's Z edge");
+        helper.assertTrue(maxZ - minZ + 1 >= 20 && maxZ - minZ + 1 <= 34,
+                "Legacy's rift spans 10–17 paired Z rows");
+        for (int z = minZ; z <= maxZ; z++) {
+            int row = z;
+            var xs = footprint.stream().filter(pos -> pos.getZ() == row)
+                    .mapToInt(BlockPos::getX).sorted().toArray();
+            helper.assertTrue(xs.length > 0, "Every Z row must contain portal tiles");
+            for (int i = 1; i < xs.length; i++)
+                helper.assertValueEqual(xs[i], xs[i - 1] + 1,
+                        "Each jagged Legacy row remains contiguous");
+        }
+        helper.succeed();
+    }
+
+    private static ResourceLocation id(String path) {
+        return ResourceLocation.fromNamespaceAndPath(Rivencraft.MOD_ID, path);
+    }
+
+    private static boolean hasRandomFissure(long seed, ResourceLocation terrain,
+                                             net.minecraft.core.RegistryAccess registries) {
+        return AgeFeatureSelection.randomChoices(seed, AgeRuntimeProfiles.resolve(terrain), registries).stream()
+                .anyMatch(choice -> choice.id().equals(AgeFeatureSelection.STAR_FISSURES));
+    }
+
+    private static WritingEntry page(String path) {
+        return WritingEntry.symbol(new SymbolReference(id(path)));
+    }
+}

src/main/resources/assets/rivencraft/blockstates/star_fissure.json

@@ -0,0 +1 @@
+{"variants":{"":{"model":"rivencraft:block/star_fissure"}}}

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

@@ -289,6 +289,9 @@
   "symbol.rivencraft.feature.obelisks.description": "Add rare tall obelisks on exposed solid ground, with a random or selected block material.",
   "symbol.rivencraft.feature.crystal_formations": "Crystal Formations",
   "symbol.rivencraft.feature.crystal_formations.description": "Add blue crystal formations whose budding blocks grow harvestable clusters.",
+  "symbol.rivencraft.feature.star_fissures": "Star Fissures",
+  "symbol.rivencraft.feature.star_fissures.description": "Open a starry fissure near this Age's spawn that links back to the Overworld.",
+  "block.rivencraft.star_fissure": "Star Fissure",
   "block.rivencraft.crystal_block": "Crystal Block",
   "block.rivencraft.budding_crystal": "Budding Crystal",
   "block.rivencraft.small_crystal_bud": "Small Crystal Bud",

src/main/resources/assets/rivencraft/models/block/star_fissure.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/end_portal"}

src/main/resources/assets/rivencraft/sounds.json

@@ -6,5 +6,9 @@
         "name": "rivencraft:linking/link"
       }
     ]
+  },
+  "linking.link-fissure": {
+    "category": "player",
+    "sounds": [{"name": "rivencraft:linking/link-fissure"}]
   }
 }

src/main/resources/data/rivencraft/rivencraft/symbols/feature/star_fissures.json

@@ -0,0 +1,8 @@
+{
+  "schema_version": 2,
+  "name": "symbol.rivencraft.feature.star_fissures",
+  "description": "symbol.rivencraft.feature.star_fissures.description",
+  "category": "rivencraft:feature",
+  "semantics": { "role": "feature", "value": "rivencraft:star_fissures" },
+  "poem": "Star Fissure World Home"
+}