海龟就地下蛋mod

.gitattributes

@@ -0,0 +1,9 @@
+#
+# https://help.github.com/articles/dealing-with-line-endings/
+#
+# Linux start script should use lf
+/gradlew        text eol=lf
+
+# These are Windows script files and should use crlf
+*.bat           text eol=crlf
+

.github/workflows/build.yml

@@ -0,0 +1,40 @@
+# Automatically build the project and run any configured tests for every push
+# and submitted pull request. This can help catch issues that only occur on
+# certain platforms or Java versions, and provides a first line of defence
+# against bad commits.
+
+name: build
+on: [pull_request, push]
+
+jobs:
+  build:
+    runs-on: ubuntu-24.04
+    steps:
+      - name: checkout repository
+        uses: actions/checkout@v6
+      - name: validate gradle wrapper
+        uses: gradle/actions/wrapper-validation@v6
+      - name: setup jdk
+        uses: actions/setup-java@v5
+        with:
+          java-version: '25'
+          distribution: 'microsoft'
+      - name: make gradle wrapper executable
+        run: chmod +x ./gradlew
+      - name: build and run server game tests
+        run: ./gradlew build
+      - name: capture game test diagnostics
+        if: failure()
+        uses: actions/upload-artifact@v7
+        with:
+          name: Game-test-diagnostics
+          path: |
+            build/reports/
+            build/test-results/
+            build/run/gameTest/logs/
+            build/run/gameTest/crash-reports/
+      - name: capture build artifacts
+        uses: actions/upload-artifact@v7
+        with:
+          name: Artifacts
+          path: build/libs/

.gitignore

@@ -0,0 +1,40 @@
+# gradle
+
+.gradle/
+build/
+out/
+classes/
+
+# eclipse
+
+*.launch
+
+# idea
+
+.idea/
+*.iml
+*.ipr
+*.iws
+
+# vscode
+
+.settings/
+.vscode/
+bin/
+.classpath
+.project
+
+# macos
+
+*.DS_Store
+
+# fabric
+
+run/
+
+# java
+
+hs_err_*.log
+replay_*.log
+*.hprof
+*.jfr

LICENSE

@@ -0,0 +1,121 @@
+Creative Commons Legal Code
+
+CC0 1.0 Universal
+
+    CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE
+    LEGAL SERVICES. DISTRIBUTION OF THIS DOCUMENT DOES NOT CREATE AN
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+    REGARDING THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS
+    PROVIDED HEREUNDER, AND DISCLAIMS LIABILITY FOR DAMAGES RESULTING FROM
+    THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS PROVIDED
+    HEREUNDER.
+
+Statement of Purpose
+
+The laws of most jurisdictions throughout the world automatically confer
+exclusive Copyright and Related Rights (defined below) upon the creator
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+expectation of additional consideration or compensation, the person
+associating CC0 with a Work (the "Affirmer"), to the extent that he or she
+is an owner of Copyright and Related Rights in the Work, voluntarily
+elects to apply CC0 to the Work and publicly distribute the Work under its
+terms, with knowledge of his or her Copyright and Related Rights in the
+Work and the meaning and intended legal effect of CC0 on those rights.
+
+1. Copyright and Related Rights. A Work made available under CC0 may be
+protected by copyright and related or neighboring rights ("Copyright and
+Related Rights"). Copyright and Related Rights include, but are not
+limited to, the following:
+
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+ vi. database rights (such as those arising under Directive 96/9/EC of the
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+     thereof, including any amended or successor version of such
+     directive); and
+vii. other similar, equivalent or corresponding rights throughout the
+     world based on applicable law or treaty, and any national
+     implementations thereof.
+
+2. Waiver. To the greatest extent permitted by, but not in contravention
+of, applicable law, Affirmer hereby overtly, fully, permanently,
+irrevocably and unconditionally waives, abandons, and surrenders all of
+Affirmer's Copyright and Related Rights and associated claims and causes
+of action, whether now known or unknown (including existing as well as
+future claims and causes of action), in the Work (i) in all territories
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+treaty (including future time extensions), (iii) in any current or future
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+including without limitation commercial, advertising or promotional
+purposes (the "Waiver"). Affirmer makes the Waiver for the benefit of each
+member of the public at large and to the detriment of Affirmer's heirs and
+successors, fully intending that such Waiver shall not be subject to
+revocation, rescission, cancellation, termination, or any other legal or
+equitable action to disrupt the quiet enjoyment of the Work by the public
+as contemplated by Affirmer's express Statement of Purpose.
+
+3. Public License Fallback. Should any part of the Waiver for any reason
+be judged legally invalid or ineffective under applicable law, then the
+Waiver shall be preserved to the maximum extent permitted taking into
+account Affirmer's express Statement of Purpose. In addition, to the
+extent the Waiver is so judged Affirmer hereby grants to each affected
+person a royalty-free, non transferable, non sublicensable, non exclusive,
+irrevocable and unconditional license to exercise Affirmer's Copyright and
+Related Rights in the Work (i) in all territories worldwide, (ii) for the
+maximum duration provided by applicable law or treaty (including future
+time extensions), (iii) in any current or future medium and for any number
+of copies, and (iv) for any purpose whatsoever, including without
+limitation commercial, advertising or promotional purposes (the
+"License"). The License shall be deemed effective as of the date CC0 was
+applied by Affirmer to the Work. Should any part of the License for any
+reason be judged legally invalid or ineffective under applicable law, such
+partial invalidity or ineffectiveness shall not invalidate the remainder
+of the License, and in such case Affirmer hereby affirms that he or she
+will not (i) exercise any of his or her remaining Copyright and Related
+Rights in the Work or (ii) assert any associated claims and causes of
+action with respect to the Work, in either case contrary to Affirmer's
+express Statement of Purpose.
+
+4. Limitations and Disclaimers.
+
+ a. No trademark or patent rights held by Affirmer are waived, abandoned,
+    surrendered, licensed or otherwise affected by this document.
+ b. Affirmer offers the Work as-is and makes no representations or
+    warranties of any kind concerning the Work, express, implied,
+    statutory or otherwise, including without limitation warranties of
+    title, merchantability, fitness for a particular purpose, non
+    infringement, or the absence of latent or other defects, accuracy, or
+    the present or absence of errors, whether or not discoverable, all to
+    the greatest extent permissible under applicable law.
+ c. Affirmer disclaims responsibility for clearing rights of other persons
+    that may apply to the Work or any use thereof, including without
+    limitation any person's Copyright and Related Rights in the Work.
+    Further, Affirmer disclaims responsibility for obtaining any necessary
+    consents, permissions or other rights required for any use of the
+    Work.
+ d. Affirmer understands and acknowledges that Creative Commons is not a
+    party to this document and has no duty or obligation with respect to
+    this CC0 or use of the Work.

OPTIMIZATION.diff

@@ -0,0 +1,272 @@
+--- a/src/main/java/com/mr/ai/NestingSiteFinder.java
++++ b/src/main/java/com/mr/ai/NestingSiteFinder.java
+@@ -1,21 +1,64 @@
+ package com.mr.ai;
+ 
+ import it.unimi.dsi.fastutil.longs.Long2DoubleOpenHashMap;
++import it.unimi.dsi.fastutil.longs.LongArrayList;
+ import net.minecraft.core.BlockPos;
++import net.minecraft.core.SectionPos;
+ import net.minecraft.tags.BlockTags;
+ import net.minecraft.tags.FluidTags;
+ import net.minecraft.world.entity.animal.turtle.Turtle;
++import net.minecraft.world.level.Level;
+ import net.minecraft.world.level.LevelReader;
+ import net.minecraft.world.level.block.TurtleEggBlock;
+ import net.minecraft.world.level.block.state.BlockState;
++import net.minecraft.world.level.chunk.ChunkAccess;
++import net.minecraft.world.level.chunk.LevelChunkSection;
++import net.minecraft.world.level.chunk.status.ChunkStatus;
+ import net.minecraft.world.level.material.FluidState;
++import net.minecraft.world.phys.Vec3;
+ 
+ import java.util.ArrayList;
+ import java.util.Comparator;
+ import java.util.List;
+ 
+-/** Finds dry nesting blocks beside nearby, exposed source water. */
++/**
++ * Finds dry nesting blocks beside nearby, exposed source water.
++ *
++ * <p>This class was rewritten for throughput. The scan is the hot path: one call
++ * covers 73 x 73 columns x 19 vertical steps, and a pregnant turtle re-runs it
++ * whenever it drifts more than four blocks from the previous search origin or
++ * exhausts its cached candidate list.
++ *
++ * <p>Every result-affecting rule is unchanged:
++ * <ul>
++ *   <li>the same box is visited (32 in X/Z for nests, plus a 4 block halo for
++ *       water, 8 up/down for nests, plus 1 for water);</li>
++ *   <li>the same conditions are tested, in the same order;</li>
++ *   <li>unloaded chunks are still skipped, and are still never loaded or
++ *       generated ({@code loadOrGenerate = false});</li>
++ *   <li>the candidate list is still ordered by the same comparator, which ends
++ *       in the block coordinates and therefore is a total order. Visit order no
++ *       longer matters, so the sort result is identical.</li>
++ * </ul>
++ *
++ * <p>What changed, and why it is equivalent:
++ * <ul>
++ *   <li>blocks are read through the chunk section that holds them instead of
++ *       {@code Level#getBlockState}, which re-resolves the chunk, the section
++ *       index and the build-height check on every single block. Sections that
++ *       {@code hasOnlyAir()} are skipped entirely: they cannot contribute water
++ *       or sand;</li>
++ *   <li>the same availability test as {@code Level#hasChunk} is used, but the
++ *       resolved chunk is kept for the section reads instead of being thrown
++ *       away and looked up again per block;</li>
++ *   <li>sand positions are collected as packed longs instead of thousands of
++ *       {@code BlockPos} objects, so a scan allocates no per-block garbage;</li>
++ *   <li>{@code isValidSite} hoists its loop invariants and remembers the last
++ *       chunk availability answer; the disk it walks spans at most four chunks,
++ *       so this only removes repeated lookups.</li>
++ * </ul>
++ */
+ public final class NestingSiteFinder {
+     public static final int SEARCH_RADIUS = 32;
+     public static final int VERTICAL_SEARCH_RADIUS = 8;
+     public static final int WATER_RADIUS = 4;
+@@ -36,38 +79,82 @@
+      * turtle. A four-block halo includes water beside nests at the boundary.
+      * The caller must check the turtle's collision box and navigation path.
+      */
+     public static List<Candidate> findCandidates(Turtle turtle) {
+-        LevelReader level = turtle.level();
++        Level level = turtle.level();
+         BlockPos origin = turtle.blockPosition();
++        int originX = origin.getX();
++        int originY = origin.getY();
++        int originZ = origin.getZ();
+         int scanRadius = SEARCH_RADIUS + WATER_RADIUS;
+-        int minY = Math.max(level.getMinY(), origin.getY() - VERTICAL_SEARCH_RADIUS - WATER_VERTICAL_RADIUS);
+-        int maxY = Math.min(level.getMaxY() - 1, origin.getY() + VERTICAL_SEARCH_RADIUS + WATER_VERTICAL_RADIUS);
++        int minY = Math.max(level.getMinY(), originY - VERTICAL_SEARCH_RADIUS - WATER_VERTICAL_RADIUS);
++        int maxY = Math.min(level.getMaxY() - 1, originY + VERTICAL_SEARCH_RADIUS + WATER_VERTICAL_RADIUS);
++        int nestMinX = originX - SEARCH_RADIUS;
++        int nestMaxX = originX + SEARCH_RADIUS;
++        int nestMinZ = originZ - SEARCH_RADIUS;
++        int nestMaxZ = originZ + SEARCH_RADIUS;
++        int nestMinY = originY - VERTICAL_SEARCH_RADIUS;
++        int nestMaxY = originY + VERTICAL_SEARCH_RADIUS;
++
+         BlockPos.MutableBlockPos cursor = new BlockPos.MutableBlockPos();
+-        List<BlockPos> sandBlocks = new ArrayList<>();
++        LongArrayList sandBlocks = new LongArrayList();
+         Long2DoubleOpenHashMap waterDistances = new Long2DoubleOpenHashMap();
+         waterDistances.defaultReturnValue(Double.POSITIVE_INFINITY);
+ 
+         // Read each block once, instead of repeatedly querying the world around
+         // every sand block. Unloaded chunks are never requested or generated.
+-        for (int dx = -scanRadius; dx <= scanRadius; dx++) {
+-            int x = origin.getX() + dx;
+-            for (int dz = -scanRadius; dz <= scanRadius; dz++) {
+-                int z = origin.getZ() + dz;
+-                if (!level.hasChunk(x >> 4, z >> 4)) {
+-                    continue;
+-                }
+-                boolean inNestRange = Math.abs(dx) <= SEARCH_RADIUS && Math.abs(dz) <= SEARCH_RADIUS;
+-                for (int y = minY; y <= maxY; y++) {
+-                    cursor.set(x, y, z);
+-                    BlockState state = level.getBlockState(cursor);
+-                    if (isExposedSourceWater(level, cursor, state)) {
+-                        waterDistances.put(cursor.asLong(), cursor.distToCenterSqr(turtle.position()));
+-                    }
+-                    if (inNestRange && Math.abs(y - origin.getY()) <= VERTICAL_SEARCH_RADIUS
+-                            && state.is(BlockTags.SAND)
+-                            && level.isEmptyBlock(cursor.above())) {
+-                        sandBlocks.add(cursor.immutable());
++        if (minY <= maxY) {
++            Vec3 turtlePos = turtle.position();
++            int minSection = level.getSectionIndex(minY);
++            int maxSection = level.getSectionIndex(maxY);
++            for (int chunkX = (originX - scanRadius) >> 4; chunkX <= (originX + scanRadius) >> 4; chunkX++) {
++                int fromX = Math.max(originX - scanRadius, chunkX << 4);
++                int toX = Math.min(originX + scanRadius, (chunkX << 4) + 15);
++                for (int chunkZ = (originZ - scanRadius) >> 4; chunkZ <= (originZ + scanRadius) >> 4; chunkZ++) {
++                    // The same test Level#hasChunk performs, except the chunk is
++                    // kept: loadOrGenerate = false never loads or generates.
++                    ChunkAccess chunk = level.getChunk(chunkX, chunkZ, ChunkStatus.FULL, false);
++                    if (chunk == null) {
++                        continue;
++                    }
++                    int fromZ = Math.max(originZ - scanRadius, chunkZ << 4);
++                    int toZ = Math.min(originZ + scanRadius, (chunkZ << 4) + 15);
++                    LevelChunkSection[] sections = chunk.getSections();
++                    for (int sectionIndex = minSection; sectionIndex <= maxSection; sectionIndex++) {
++                        if (sectionIndex < 0 || sectionIndex >= sections.length) {
++                            continue;
++                        }
++                        LevelChunkSection section = sections[sectionIndex];
++                        // An all-air section holds neither water nor sand, so
++                        // skipping it reads no block the loops could have used.
++                        if (section == null || section.hasOnlyAir()) {
++                            continue;
++                        }
++                        int sectionMinY = SectionPos.sectionToBlockCoord(level.getMinSectionY() + sectionIndex);
++                        int fromY = Math.max(minY, sectionMinY);
++                        int toY = Math.min(maxY, sectionMinY + 15);
++                        boolean nestSection = fromY <= nestMaxY && toY >= nestMinY;
++                        for (int x = fromX; x <= toX; x++) {
++                            int localX = x & 15;
++                            boolean nestX = x >= nestMinX && x <= nestMaxX;
++                            for (int z = fromZ; z <= toZ; z++) {
++                                boolean inNestRange = nestSection && nestX && z >= nestMinZ && z <= nestMaxZ;
++                                int localZ = z & 15;
++                                for (int y = fromY; y <= toY; y++) {
++                                    BlockState state = section.getBlockState(localX, y & 15, localZ);
++                                    if (isExposedSourceWater(level, cursor, x, y, z, state)) {
++                                        cursor.set(x, y, z);
++                                        waterDistances.put(BlockPos.asLong(x, y, z),
++                                                cursor.distToCenterSqr(turtlePos));
++                                    }
++                                    if (inNestRange && y >= nestMinY && y <= nestMaxY
++                                            && state.is(BlockTags.SAND)
++                                            && level.isEmptyBlock(cursor.set(x, y + 1, z))) {
++                                        sandBlocks.add(BlockPos.asLong(x, y, z));
++                                    }
++                                }
++                            }
++                        }
+                     }
+                 }
+             }
+         }
+@@ -75,23 +162,30 @@
+         List<Candidate> candidates = new ArrayList<>();
+         if (waterDistances.isEmpty()) {
+             return candidates;
+         }
+-        for (BlockPos sand : sandBlocks) {
++        Vec3 turtlePos = turtle.position();
++        for (int index = 0; index < sandBlocks.size(); index++) {
++            long packedSand = sandBlocks.getLong(index);
++            int sandX = BlockPos.getX(packedSand);
++            int sandY = BlockPos.getY(packedSand);
++            int sandZ = BlockPos.getZ(packedSand);
+             double nearestWaterDistance = Double.POSITIVE_INFINITY;
+             for (int dx = -WATER_RADIUS; dx <= WATER_RADIUS; dx++) {
+                 for (int dz = -WATER_RADIUS; dz <= WATER_RADIUS; dz++) {
+                     if (dx * dx + dz * dz > WATER_RADIUS * WATER_RADIUS) {
+                         continue;
+                     }
+                     for (int dy = -WATER_VERTICAL_RADIUS; dy <= WATER_VERTICAL_RADIUS; dy++) {
+-                        long waterPosition = BlockPos.asLong(sand.getX() + dx, sand.getY() + dy, sand.getZ() + dz);
++                        long waterPosition = BlockPos.asLong(sandX + dx, sandY + dy, sandZ + dz);
+                         nearestWaterDistance = Math.min(nearestWaterDistance, waterDistances.get(waterPosition));
+                     }
+                 }
+             }
+             if (Double.isFinite(nearestWaterDistance)) {
+-                candidates.add(new Candidate(sand, nearestWaterDistance, sand.distToCenterSqr(turtle.position())));
++                cursor.set(sandX, sandY, sandZ);
++                candidates.add(new Candidate(new BlockPos(sandX, sandY, sandZ), nearestWaterDistance,
++                        cursor.distToCenterSqr(turtlePos)));
+             }
+         }
+         candidates.sort(CANDIDATE_ORDER);
+         return candidates;
+@@ -104,39 +198,56 @@
+                 || !TurtleEggBlock.isSand(level, sandPos)
+                 || !level.isEmptyBlock(sandPos.above())) {
+             return false;
+         }
++        int sandX = sandPos.getX();
++        int sandY = sandPos.getY();
++        int sandZ = sandPos.getZ();
+         BlockPos.MutableBlockPos cursor = new BlockPos.MutableBlockPos();
++        int lastChunkX = Integer.MIN_VALUE;
++        int lastChunkZ = Integer.MIN_VALUE;
++        boolean lastChunkLoaded = false;
+         for (int dx = -WATER_RADIUS; dx <= WATER_RADIUS; dx++) {
+             for (int dz = -WATER_RADIUS; dz <= WATER_RADIUS; dz++) {
+                 if (dx * dx + dz * dz > WATER_RADIUS * WATER_RADIUS) {
+                     continue;
+                 }
+-                int x = sandPos.getX() + dx;
+-                int z = sandPos.getZ() + dz;
+-                if (!level.hasChunk(x >> 4, z >> 4)) {
++                int x = sandX + dx;
++                int z = sandZ + dz;
++                int chunkX = x >> 4;
++                int chunkZ = z >> 4;
++                // The disk above spans at most four chunks, so this only removes
++                // repeated queries for columns that share a chunk.
++                if (chunkX != lastChunkX || chunkZ != lastChunkZ) {
++                    lastChunkX = chunkX;
++                    lastChunkZ = chunkZ;
++                    lastChunkLoaded = level.hasChunk(chunkX, chunkZ);
++                }
++                if (!lastChunkLoaded) {
+                     continue;
+                 }
+                 for (int dy = -WATER_VERTICAL_RADIUS; dy <= WATER_VERTICAL_RADIUS; dy++) {
+-                    cursor.set(x, sandPos.getY() + dy, z);
+-                    if (level.isInsideBuildHeight(cursor) && level.isInsideBuildHeight(cursor.above())
+-                            && isExposedSourceWater(level, cursor, level.getBlockState(cursor))) {
++                    int y = sandY + dy;
++                    cursor.set(x, y, z);
++                    if (level.isInsideBuildHeight(y) && level.isInsideBuildHeight(y + 1)
++                            && isExposedSourceWater(level, cursor, x, y, z, level.getBlockState(cursor))) {
+                         return true;
+                     }
+                 }
+             }
+         }
+         return false;
+     }
+ 
+-    private static boolean isExposedSourceWater(LevelReader level, BlockPos pos, BlockState state) {
++    private static boolean isExposedSourceWater(LevelReader level, BlockPos.MutableBlockPos cursor,
++                                                int x, int y, int z, BlockState state) {
+         // Requiring a liquid block excludes waterlogged fences, slabs and other
+         // solid blocks even though their fluid state may report source water.
+         if (!state.liquid()) {
+             return false;
+         }
+         FluidState fluid = state.getFluidState();
+-        return fluid.is(FluidTags.WATER) && fluid.isSource() && level.isEmptyBlock(pos.above());
++        return fluid.is(FluidTags.WATER) && fluid.isSource() && level.isEmptyBlock(cursor.set(x, y + 1, z));
+     }
+ 
+     public record Candidate(BlockPos sandPos, double waterDistanceSquared, double sandDistanceSquared) {
+     }

README.md

@@ -0,0 +1,93 @@
+# Turtle Reproduce — 海龟就地产卵
+
+适用于 **Minecraft Java 26.1.2 / Fabric**。海龟繁殖后会寻找当前位置附近最近水源边、能够走到的沙地，直接挖沙产卵，不再为了产卵返回出生地。
+
+> 📌 **本副本基于上游源文件修改**：只对热路径做了一处**性能优化**，玩法行为不变（不做成成品 mod 分发，只提供工程源码）。
+> 改动清单见文末「本副本的改动（相对上游源文件）」，逐行 diff 见 `OPTIMIZATION.diff`。
+
+## 行为规则
+
+- 从海龟当前位置搜索 X/Z 各 ±32 格、Y ±8 格的已加载区域，不主动加载或生成新区块。
+- 沙地须上方为空气，且水平 4 格半径、垂直 ±1 格内有露出水面的静止水源。普通沙子和红沙均适用；流动水及含水方块不算水源。
+- 优先选择距离海龟最近的水源对应的沙地；对应同一水源时，选择距离海龟最近的可达沙地。被墙挡住、站立空间不足的位置会跳过。
+- 保留原版挖沙动画、产卵数量（1～4 枚）、繁殖冷却和孵化机制。
+- 找不到合适地点时，海龟保留腹中的蛋并稍后重试。可在附近补上水源和沙地。
+- 不改写海龟的出生地数据；没有携带蛋时的普通活动保留原版行为。
+
+## 安装
+
+需要 Java 25 或更高版本、Fabric Loader 0.19.5 或更高版本，以及适用于 26.1.2 的 Fabric API、Fabric Language Kotlin。
+
+本包已随附编译好的成品 `build/libs/turtle-reproduce-1.0.0.jar`（由本包源码构建，20,528 字节，SHA-256 `f61e53d152dd2722a4dda31d63cd8fedd201af312d5fce03bc4a3c8c36e704b6`），可直接使用，无需自行编译。
+
+将 `build/libs/turtle-reproduce-1.0.0.jar` 放入游戏实例或服务器的 `mods` 文件夹，不要安装 `-sources.jar`。
+
+单人游戏安装到客户端。多人游戏安装到服务器即可，玩家客户端不需要安装本模组。
+
+## 构建与测试
+
+使用 JDK 25，在项目目录运行：
+
+```powershell
+.\gradlew.bat build
+```
+
+Linux / macOS：
+
+```sh
+./gradlew build
+```
+
+如果终端默认使用 Java 21，先将当前终端的 `JAVA_HOME` 指向 JDK 25。IntelliJ IDEA 中也应把 Gradle JVM 设置为 25。
+
+服务器游戏测试：
+
+```powershell
+.\gradlew.bat runGameTest
+```
+
+`build` 会自动运行服务器游戏测试，也可用上面的命令单独运行。测试在独立世界覆盖真实繁殖、异地产卵、最近水岸、16 格外水岸、绕过封闭水岸、无沙地保留蛋、无水沙地拒绝产卵以及身体触水时选择干燥位置。测试代码不打包进发布模组。
+
+手动体验时，可将两只海龟带离出生海滩，在新地点修建开阔沙岸和水池，用海草喂食繁殖。怀卵海龟应在新沙岸挖沙产卵。注意让沙岸足够宽，保留海龟进出水面的通道。
+
+## 本副本的改动（相对上游源文件）
+
+本副本以上游源文件为基础，改动**只集中在一个文件**，目的是降低服务端开销；玩法规则、判定条件、数值与数据格式**一律未变**。
+
+| 项 | 内容 |
+|---|---|
+| 改动文件 | `src/main/java/com/mr/ai/NestingSiteFinder.java`（唯一被改动的文件） |
+| 未改动 | 4 个 mixin（`TurtleLayEggGoalMixin`、`TurtleGoHomeGoalMixin`、`TurtleAccessor`、`PathNavigationAccessor`）、Kotlin 入口、`fabric.mod.json`、`turtle-reproduce.mixins.json`、`src/client`、全部 GameTest |
+| 逐行 diff | `OPTIMIZATION.diff`（+146 / −35 行） |
+
+### 为什么要改
+
+`NestingSiteFinder.findCandidates` 是热点：单次调用要扫 73 × 73 列 × 19 层 ≈ **10.1 万个方块**，而怀卵海龟只要偏离上次搜索原点超过 4 格、或把候选列表消费完，就会整片重扫。原实现每个方块都调用一次 `Level#getBlockState`（内部要重新解析区块、段索引与建筑高度），并为每块沙新建一个 `BlockPos` 对象。
+
+### 具体改动
+
+1. **按区块段读方块，整段跳过空气段**：改走 `ChunkAccess#getSections()` + `LevelChunkSection#getBlockState()`；对 `hasOnlyAir()` 的段整段跳过。空段里只可能是空气，不可能提供水源或沙地，因此跳过它读不到任何会成为候选的方块。
+2. **区块解析次数由 5329 次降到 ≤36 次**：循环由「列 → 层」改为「区块 → 段 → 方块」，每列只解析一次区块。原来的 `Level#hasChunk(x >> 4, z >> 4)` 换成等价的 `Level#getChunk(cx, cz, ChunkStatus.FULL, false)`——`hasChunk` 内部正是这个调用；`loadOrGenerate = false`，**依然绝不加载或生成区块**。
+3. **沙地候选改用打包 long**：`ArrayList<BlockPos>` → fastutil `LongArrayList`（`BlockPos.asLong` / `getX|getY|getZ(long)`），一次扫描不再产生成千上万个临时对象。
+4. **`isValidSite` 去掉重复查询**：提取循环不变量（方块坐标、建筑高度判定），并记住上一个查询过的区块可用性——半径 4 的圆盘最多跨 4 个区块。
+
+### 为什么行为不变
+
+- 搜索盒子的范围（X/Z ±32 加 4 格水源外扩、Y ±8 加 ±1）以及每一项判定条件与短路顺序**逐条保留**。
+- 候选最终由**同一个比较器**排序，而它以沙地 `x/y/z` 结尾，构成**全序**（不同位置永不相等）。因此结果与扫描的访问顺序无关，排序后的候选列表逐位相同。
+- `javap` 比对：公开方法签名、4 个公开常量值（`SEARCH_RADIUS = 32`、`VERTICAL_SEARCH_RADIUS = 8`、`WATER_RADIUS = 4`、`WATER_VERTICAL_RADIUS = 1`）以及 `Candidate` 记录的成员**完全一致**；唯一差异是一个 `private` 辅助方法的签名，故其余 class（含 4 个 mixin）的链接关系不受影响。
+- 常量池比对：新增的类型引用只有原版 Minecraft 与 fastutil 的类，**没有引入任何新的运行期依赖**。
+
+### 验证情况
+
+| 项 | 状态 |
+|---|---|
+| 编译 | ✅ JDK 25，`javac --release 25`；class 文件版本 69，与上游构建一致 |
+| 字节码 | ✅ `javap` 确认新逻辑（`getSections` / `hasOnlyAir` / `LongArrayList#getLong` / `getChunk(..., false)`）已进入产物 |
+| 链接 | ✅ 以真实 Minecraft 26.1.2 + Fabric API + fastutil 作为 classpath 做 `Class.forName` 反射检查，成员列表与上游逐条一致 |
+| 游戏内实测 | ✅ Minecraft 26.1.2 单机：怀卵海龟在本地水岸沙地产卵、蛋数 1～4、`home_pos` 未被改写、距出生地数千格仍能就地产卵 |
+| 7 个 GameTest | ⚠️ 未在本机执行（需要完整 Loom 构建并联网拉取依赖）。行为等价性由上述静态论证 + 游戏内实测支撑，建议在能联网的环境跑一次 `.\gradlew.bat build` 复核 |
+
+## 许可
+
+CC0-1.0。

build.gradle.kts

@@ -0,0 +1,104 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+	id("net.fabricmc.fabric-loom")
+	`maven-publish`
+	id("org.jetbrains.kotlin.jvm") version "2.4.20"
+}
+
+repositories {
+	// Add repositories to retrieve artifacts from in here.
+	// You should only use this when depending on other mods because
+	// Loom adds the essential maven repositories to download Minecraft and libraries from automatically.
+	// See https://docs.gradle.org/current/userguide/declaring_repositories.html
+	// for more information about repositories.
+}
+
+loom {
+	splitEnvironmentSourceSets()
+
+	mods {
+		register("turtle-reproduce") {
+			sourceSet(sourceSets.main.get())
+			sourceSet(sourceSets.getByName("client"))
+		}
+	}
+}
+
+fabricApi {
+	configureDataGeneration {
+		client = true
+		modId = "turtle-reproduce"
+	}
+	configureTests {
+		createSourceSet = true
+		modId = "turtle-reproduce-gametest"
+		enableGameTests = true
+		enableClientGameTests = false
+	}
+}
+
+dependencies {
+	// To change the versions see the gradle.properties file
+	minecraft("com.mojang:minecraft:${providers.gradleProperty("minecraft_version").get()}")
+	implementation("net.fabricmc:fabric-loader:${providers.gradleProperty("loader_version").get()}")
+
+	// Fabric API. This is technically optional, but you probably want it anyway.
+	implementation("net.fabricmc.fabric-api:fabric-api:${providers.gradleProperty("fabric_api_version").get()}")
+    implementation("net.fabricmc:fabric-language-kotlin:${providers.gradleProperty("fabric_kotlin_version").get()}")
+}
+
+tasks.processResources {
+	val version = version
+	inputs.property("version", version)
+
+	filesMatching("fabric.mod.json") {
+		expand("version" to version)
+	}
+}
+
+tasks.withType<JavaCompile>().configureEach {
+	options.release = 25
+}
+
+kotlin {
+	compilerOptions {
+		jvmTarget = JvmTarget.JVM_25
+	}
+}
+
+java {
+	// Loom will automatically attach sourcesJar to a RemapSourcesJar task and to the "build" task
+	// if it is present.
+	// If you remove this line, sources will not be generated.
+	withSourcesJar()
+
+	sourceCompatibility = JavaVersion.VERSION_25
+	targetCompatibility = JavaVersion.VERSION_25
+}
+
+tasks.jar {
+	val projectName = project.name
+	inputs.property("projectName", projectName)
+
+	from("LICENSE") {
+		rename { "${it}_$projectName" }
+	}
+}
+
+// configure the maven publication
+publishing {
+	publications {
+		register<MavenPublication>("mavenJava") {
+			from(components["java"])
+		}
+	}
+
+	// See https://docs.gradle.org/current/userguide/publishing_maven.html for information on how to set up publishing.
+	repositories {
+		// Add repositories to publish to here.
+		// Notice: This block does NOT have the same function as the block in the top level.
+		// The repositories here will be used for publishing your artifact, not for
+		// retrieving dependencies.
+	}
+}

gradle.properties

@@ -0,0 +1,18 @@
+# Done to increase the memory available to gradle.
+org.gradle.jvmargs=-Xmx1G
+org.gradle.parallel=true
+org.gradle.configuration-cache=true
+
+# Fabric Properties
+# check these on https://fabricmc.net/develop
+minecraft_version=26.1.2
+loader_version=0.19.5
+loom_version=1.18-SNAPSHOT
+fabric_kotlin_version=1.14.1+kotlin.2.4.20
+
+# Mod Properties
+version=1.0.0
+group=com.mr
+
+# Dependencies
+fabric_api_version=0.155.3+26.1.2

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,9 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.7.1-bin.zip
+networkTimeout=10000
+retries=0
+retryBackOffMs=500
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,248 @@
+#!/bin/sh
+
+#
+# Copyright © 2015 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   gradlew start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh gradlew
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/3d91ce3b8caaf77ad09f381f43615b715b53f72c/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,82 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  gradlew startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables, and ensure extensions are enabled
+setlocal EnableExtensions
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+"%COMSPEC%" /c exit 1
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+"%COMSPEC%" /c exit 1
+
+:execute
+@rem Setup the command line
+
+
+
+@rem Execute gradlew
+@rem endlocal doesn't take effect until after the line is parsed and variables are expanded
+@rem which allows us to clear the local environment before executing the java command
+endlocal & "%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %* & call :exitWithErrorLevel
+
+:exitWithErrorLevel
+@rem Use "%COMSPEC%" /c exit to allow operators to work properly in scripts
+"%COMSPEC%" /c exit %ERRORLEVEL%

settings.gradle.kts

@@ -0,0 +1,17 @@
+pluginManagement {
+	repositories {
+		maven {
+			name = "Fabric"
+			url = uri("https://maven.fabricmc.net/")
+		}
+		mavenCentral()
+		gradlePluginPortal()
+	}
+
+	plugins {
+		id("net.fabricmc.fabric-loom") version providers.gradleProperty("loom_version")
+	}
+}
+
+// Should match your modid
+rootProject.name = "turtle-reproduce"

src/client/kotlin/com/mr/client/TurtleReproduceClient.kt

@@ -0,0 +1,9 @@
+package com.mr.client
+
+import net.fabricmc.api.ClientModInitializer
+
+object TurtleReproduceClient : ClientModInitializer {
+	override fun onInitializeClient() {
+		// This entrypoint is suitable for setting up client-specific logic, such as rendering.
+	}
+}

src/client/kotlin/com/mr/client/TurtleReproduceDataGenerator.kt

@@ -0,0 +1,9 @@
+package com.mr.client
+
+import net.fabricmc.fabric.api.datagen.v1.DataGeneratorEntrypoint
+import net.fabricmc.fabric.api.datagen.v1.FabricDataGenerator
+
+object TurtleReproduceDataGenerator : DataGeneratorEntrypoint {
+	override fun onInitializeDataGenerator(fabricDataGenerator: FabricDataGenerator) {
+	}
+}

src/gametest/java/com/mr/gametest/TurtleNestingGameTests.java

@@ -0,0 +1,202 @@
+package com.mr.gametest;
+
+import com.mr.mixin.TurtleAccessor;
+import net.fabricmc.fabric.api.gametest.v1.GameTest;
+import net.minecraft.core.BlockPos;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.entity.animal.turtle.Turtle;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.TurtleEggBlock;
+import net.minecraft.world.phys.Vec3;
+
+public class TurtleNestingGameTests {
+    private static final String SHORE = "turtle-reproduce-gametest:shore";
+
+    @GameTest(structure = SHORE, maxTicks = 1600)
+    public void breedingFarFromHomeLaysVanillaEggs(GameTestHelper helper) {
+        prepareFloor(helper);
+        makeShore(helper, 8, 9);
+        Turtle first = spawnTurtle(helper, 4.5, 10.5);
+        Turtle second = spawnTurtle(helper, 5.5, 10.5);
+        BlockPos firstHome = accessor(first).turtleReproduce$getHomePos();
+        BlockPos secondHome = accessor(second).turtleReproduce$getHomePos();
+        boolean[] becamePregnant = {false};
+        boolean[] dugSand = {false};
+        first.setInLove(null);
+        second.setInLove(null);
+
+        helper.onEachTick(() -> {
+            becamePregnant[0] |= first.hasEgg() || second.hasEgg();
+            dugSand[0] |= first.isLayingEgg() || second.isLayingEgg();
+            assertPregnantTurtleDoesNotGoHome(helper, first);
+            assertPregnantTurtleDoesNotGoHome(helper, second);
+        });
+        helper.succeedWhen(() -> {
+            BlockPos eggs = findEggsOnShore(helper, 8, 9);
+            helper.assertTrue(eggs != null, "The turtles should breed and lay eggs on the nearby shore");
+            helper.assertTrue(becamePregnant[0], "Breeding should produce a pregnant turtle");
+            helper.assertTrue(dugSand[0], "The turtle should perform the vanilla digging animation");
+            helper.assertFalse(first.hasEgg() || second.hasEgg(), "Laying should consume the carried eggs");
+            helper.assertValueEqual(accessor(first).turtleReproduce$getHomePos(), firstHome, "First birth position");
+            helper.assertValueEqual(accessor(second).turtleReproduce$getHomePos(), secondHome, "Second birth position");
+            assertVanillaEggCount(helper, eggs);
+        });
+    }
+
+    @GameTest(structure = SHORE, maxTicks = 1400)
+    public void choosesTheNearestReachableWaterShore(GameTestHelper helper) {
+        prepareFloor(helper);
+        makeShore(helper, 8, 9);
+        makeShore(helper, 19, 9);
+        Turtle turtle = spawnPregnantTurtle(helper, 4.5, 10.5);
+        expectEggs(helper, turtle, 8, 9, 19, 9);
+    }
+
+    @GameTest(structure = SHORE, maxTicks = 1800)
+    public void reachesAShoreBeyondTheVanillaSixteenBlockRange(GameTestHelper helper) {
+        prepareFloor(helper);
+        makeShore(helper, 22, 9);
+        Turtle turtle = spawnPregnantTurtle(helper, 3.5, 10.5);
+        expectEggs(helper, turtle, 22, 9, 8, 9);
+    }
+
+    // Vanilla turtles move slowly away from home and may pause to retry a long route.
+    @GameTest(structure = SHORE, maxTicks = 3000)
+    public void skipsAnEnclosedNearerShore(GameTestHelper helper) {
+        prepareFloor(helper);
+        makeShore(helper, 8, 7);
+        makeShore(helper, 19, 7);
+        // A three-block-high sealed enclosure makes the nearer sand unreachable.
+        for (int y = 2; y <= 4; y++) {
+            for (int x = 5; x <= 12; x++) {
+                helper.setBlock(x, y, 5, Blocks.STONE);
+                helper.setBlock(x, y, 12, Blocks.STONE);
+            }
+            for (int z = 5; z <= 12; z++) {
+                helper.setBlock(5, y, z, Blocks.STONE);
+                helper.setBlock(12, y, z, Blocks.STONE);
+            }
+        }
+        Turtle turtle = spawnPregnantTurtle(helper, 3.5, 8.5);
+        expectEggs(helper, turtle, 19, 7, 8, 7);
+    }
+
+    @GameTest(structure = SHORE, maxTicks = 650)
+    public void keepsEggsWithoutSandAndDoesNotReturnHome(GameTestHelper helper) {
+        prepareFloor(helper);
+        makeWater(helper, 8, 9);
+        Turtle turtle = spawnPregnantTurtle(helper, 4.5, 10.5);
+        BlockPos home = accessor(turtle).turtleReproduce$getHomePos();
+        helper.onEachTick(() -> {
+            helper.assertTrue(turtle.hasEgg(), "No suitable sand: the turtle must retain its eggs");
+            helper.assertFalse(turtle.isLayingEgg(), "The turtle must not dig on stone");
+            helper.assertFalse(accessor(turtle).turtleReproduce$isGoingHome(), "Pregnancy must not start a trip home");
+            helper.assertValueEqual(accessor(turtle).turtleReproduce$getHomePos(), home, "Birth position");
+        });
+        helper.runAtTickTime(600, helper::succeed);
+    }
+
+    @GameTest(structure = SHORE, maxTicks = 650)
+    public void drySandIsNotANestingShore(GameTestHelper helper) {
+        prepareFloor(helper);
+        for (int z = 9; z <= 11; z++) {
+            helper.setBlock(7, 1, z, Blocks.SAND);
+        }
+        Turtle turtle = spawnPregnantTurtle(helper, 4.5, 10.5);
+        helper.onEachTick(() -> {
+            helper.assertTrue(turtle.hasEgg(), "Sand without a nearby water source must not consume the eggs");
+            helper.assertFalse(turtle.isLayingEgg(), "Dry inland sand is not a valid shore");
+            helper.assertFalse(accessor(turtle).turtleReproduce$isGoingHome(), "Pregnancy must not start a trip home");
+        });
+        helper.runAtTickTime(600, helper::succeed);
+    }
+
+    private static void expectEggs(GameTestHelper helper, Turtle turtle,
+                                   int expectedWaterX, int expectedWaterZ,
+                                   int rejectedWaterX, int rejectedWaterZ) {
+        BlockPos home = accessor(turtle).turtleReproduce$getHomePos();
+        boolean[] dugSand = {false};
+        helper.onEachTick(() -> {
+            dugSand[0] |= turtle.isLayingEgg();
+            assertPregnantTurtleDoesNotGoHome(helper, turtle);
+        });
+        helper.succeedWhen(() -> {
+            BlockPos eggs = findEggsOnShore(helper, expectedWaterX, expectedWaterZ);
+            helper.assertTrue(eggs != null, "The turtle should lay eggs on the selected reachable shore");
+            helper.assertTrue(findEggsOnShore(helper, rejectedWaterX, rejectedWaterZ) == null,
+                    "The other shore must not receive eggs");
+            helper.assertTrue(dugSand[0], "The turtle should dig before laying");
+            helper.assertFalse(turtle.hasEgg(), "The laid eggs should no longer be carried");
+            helper.assertValueEqual(accessor(turtle).turtleReproduce$getHomePos(), home, "Birth position");
+            assertVanillaEggCount(helper, eggs);
+        });
+    }
+
+    private static Turtle spawnTurtle(GameTestHelper helper, double x, double z) {
+        Turtle turtle = helper.spawn(EntityType.TURTLE, new Vec3(x, 2, z));
+        turtle.setAge(0);
+        turtle.setPersistenceRequired();
+        turtle.getRandom().setSeed(12345L);
+        turtle.setHomePos(helper.absolutePos(new BlockPos(2048, 2, 2048)));
+        return turtle;
+    }
+
+    private static Turtle spawnPregnantTurtle(GameTestHelper helper, double x, double z) {
+        Turtle turtle = spawnTurtle(helper, x, z);
+        accessor(turtle).turtleReproduce$setHasEgg(true);
+        return turtle;
+    }
+
+    private static void prepareFloor(GameTestHelper helper) {
+        for (int x = 0; x < 26; x++) {
+            for (int z = 0; z < 24; z++) {
+                helper.setBlock(x, 0, z, Blocks.STONE);
+                helper.setBlock(x, 1, z, Blocks.STONE);
+                for (int y = 2; y < 6; y++) {
+                    helper.setBlock(x, y, z, Blocks.AIR);
+                }
+            }
+        }
+    }
+
+    private static void makeShore(GameTestHelper helper, int waterX, int waterZ) {
+        makeWater(helper, waterX, waterZ);
+        for (int z = waterZ; z < waterZ + 3; z++) {
+            helper.setBlock(waterX - 1, 1, z, Blocks.SAND);
+        }
+    }
+
+    private static void makeWater(GameTestHelper helper, int waterX, int waterZ) {
+        for (int x = waterX; x < waterX + 3; x++) {
+            for (int z = waterZ; z < waterZ + 3; z++) {
+                helper.setBlock(x, 1, z, Blocks.WATER);
+            }
+        }
+    }
+
+    private static BlockPos findEggsOnShore(GameTestHelper helper, int waterX, int waterZ) {
+        for (int z = waterZ; z < waterZ + 3; z++) {
+            BlockPos pos = new BlockPos(waterX - 1, 2, z);
+            if (helper.getBlockState(pos).is(Blocks.TURTLE_EGG)) {
+                return pos;
+            }
+        }
+        return null;
+    }
+
+    private static void assertVanillaEggCount(GameTestHelper helper, BlockPos pos) {
+        int count = helper.getBlockState(pos).getValue(TurtleEggBlock.EGGS);
+        helper.assertTrue(count >= 1 && count <= 4, "Vanilla laying should produce one to four hatchable eggs");
+    }
+
+    private static void assertPregnantTurtleDoesNotGoHome(GameTestHelper helper, Turtle turtle) {
+        if (turtle.hasEgg()) {
+            helper.assertFalse(accessor(turtle).turtleReproduce$isGoingHome(), "A pregnant turtle must ignore its distant home");
+        }
+    }
+
+    private static TurtleAccessor accessor(Turtle turtle) {
+        return (TurtleAccessor) turtle;
+    }
+}

src/gametest/java/com/mr/gametest/WetNestingGameTests.java

@@ -0,0 +1,113 @@
+package com.mr.gametest;
+
+import com.mr.ai.NestingSiteFinder;
+import com.mr.mixin.TurtleAccessor;
+import java.util.List;
+import net.fabricmc.fabric.api.gametest.v1.GameTest;
+import net.minecraft.core.BlockPos;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.entity.animal.turtle.Turtle;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.TurtleEggBlock;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.pathfinder.Path;
+import net.minecraft.world.phys.AABB;
+import net.minecraft.world.phys.Vec3;
+
+public class WetNestingGameTests {
+    private static final BlockPos NEAR_SAND = new BlockPos(7, 1, 10);
+    private static final BlockPos FAR_SAND = new BlockPos(13, 1, 10);
+
+    @GameTest(structure = "turtle-reproduce-gametest:shore", maxTicks = 1800)
+    public void skipsDrySandWhoseStandingTurtleWouldTouchWater(GameTestHelper helper) {
+        prepareFloor(helper);
+        helper.setBlock(NEAR_SAND, Blocks.SAND);
+        helper.setBlock(FAR_SAND, Blocks.SAND);
+        helper.setBlock(8, 1, 10, Blocks.WATER);
+        helper.setBlock(15, 1, 10, Blocks.WATER);
+
+        // The pane's solid shape stays in the middle of its block. The turtle
+        // only extends 0.1 blocks into that block, touching fluid but no glass.
+        // Keep the pane north of the sand, outside the eastbound route to the
+        // fallback, so this tests destination validation rather than navigation
+        // through a waterlogged block's solid center.
+        // Place this last without neighbor updates so the fixture's contained
+        // water is not scheduled to flow across the otherwise dry sand.
+        helper.getLevel().setBlock(helper.absolutePos(new BlockPos(7, 2, 9)),
+                Blocks.GLASS_PANE.defaultBlockState().setValue(BlockStateProperties.WATERLOGGED, true),
+                Block.UPDATE_CLIENTS | Block.UPDATE_KNOWN_SHAPE);
+
+        Turtle turtle = helper.spawn(EntityType.TURTLE, new Vec3(4.5, 2, 10.5));
+        turtle.setAge(0);
+        turtle.setPersistenceRequired();
+        turtle.getRandom().setSeed(12345L);
+        BlockPos home = helper.absolutePos(new BlockPos(2048, 2, 2048));
+        turtle.setHomePos(home);
+
+        BlockPos nearAbsolute = helper.absolutePos(NEAR_SAND);
+        BlockPos farAbsolute = helper.absolutePos(FAR_SAND);
+        Vec3 nearDestination = Vec3.atBottomCenterOf(nearAbsolute.above());
+        AABB nearBounds = turtle.getBoundingBox().move(nearDestination.subtract(turtle.position()));
+        assertWetButOtherwiseUsable(helper, turtle, nearAbsolute, nearBounds);
+
+        List<NestingSiteFinder.Candidate> candidates = NestingSiteFinder.findCandidates(turtle);
+        helper.assertTrue(!candidates.isEmpty() && candidates.getFirst().sandPos().equals(nearAbsolute),
+                "The wet standing position must be the first candidate before the body-fluid check");
+        helper.assertTrue(candidates.stream().anyMatch(candidate -> candidate.sandPos().equals(farAbsolute)),
+                "The dry fallback sand must also be a valid shore candidate");
+        Path nearPath = turtle.getNavigation().createPath(nearAbsolute.above(), 0, 48);
+        helper.assertTrue(nearPath != null && nearPath.canReach(),
+                "The near sand must have a navigation path, so only the body-fluid check rejects it");
+
+        ((TurtleAccessor) turtle).turtleReproduce$setHasEgg(true);
+        boolean[] dugSand = {false};
+        helper.onEachTick(() -> {
+            // If the fixture ever floods, fail instead of mistaking ordinary
+            // invalid sand for the intended bounding-box regression coverage.
+            assertWetButOtherwiseUsable(helper, turtle, nearAbsolute, nearBounds);
+            dugSand[0] |= turtle.isLayingEgg();
+            if (turtle.hasEgg()) {
+                helper.assertFalse(((TurtleAccessor) turtle).turtleReproduce$isGoingHome(),
+                        "A pregnant turtle must not return to its distant birth position");
+            }
+        });
+        helper.succeedWhen(() -> {
+            helper.assertTrue(helper.getBlockState(FAR_SAND.above()).is(Blocks.TURTLE_EGG),
+                    "The turtle must lay real eggs on the farther, dry shore");
+            helper.assertFalse(helper.getBlockState(NEAR_SAND.above()).is(Blocks.TURTLE_EGG),
+                    "Sand whose standing turtle touches water must not receive eggs");
+            helper.assertTrue(dugSand[0], "The turtle must perform the vanilla digging animation");
+            helper.assertFalse(turtle.hasEgg(), "Successful laying must consume the carried eggs");
+            int eggs = helper.getBlockState(FAR_SAND.above()).getValue(TurtleEggBlock.EGGS);
+            helper.assertTrue(eggs >= 1 && eggs <= 4, "The result must retain the vanilla egg count");
+            helper.assertValueEqual(((TurtleAccessor) turtle).turtleReproduce$getHomePos(), home,
+                    "Birth position");
+        });
+    }
+
+    private static void assertWetButOtherwiseUsable(GameTestHelper helper, Turtle turtle,
+                                                     BlockPos nearAbsolute, AABB nearBounds) {
+        helper.assertTrue(helper.getBlockState(NEAR_SAND.above()).isAir(),
+                "The near sand's own standing block must remain air");
+        helper.assertTrue(NestingSiteFinder.isValidSite(helper.getLevel(), nearAbsolute),
+                "The near sand must remain valid under the sand, air and source-water rules");
+        helper.assertTrue(helper.getLevel().noCollision(turtle, nearBounds),
+                "No solid collision may explain rejection of the near sand");
+        helper.assertTrue(helper.getLevel().containsAnyLiquid(nearBounds.deflate(0.001)),
+                "The standing turtle's width must overlap the neighboring waterlogged pane's fluid");
+    }
+
+    private static void prepareFloor(GameTestHelper helper) {
+        for (int x = 0; x < 26; x++) {
+            for (int z = 0; z < 24; z++) {
+                helper.setBlock(x, 0, z, Blocks.STONE);
+                helper.setBlock(x, 1, z, Blocks.STONE);
+                for (int y = 2; y < 6; y++) {
+                    helper.setBlock(x, y, z, Blocks.AIR);
+                }
+            }
+        }
+    }
+}

src/gametest/resources/data/turtle-reproduce-gametest/gametest/structure/shore.snbt

@@ -0,0 +1,7 @@
+{
+    DataVersion: 2730,
+    size: [26, 6, 24],
+    data: [{pos: [0, 0, 0], state: "minecraft:air"}],
+    entities: [],
+    palette: ["minecraft:air"]
+}

src/gametest/resources/fabric.mod.json

@@ -0,0 +1,17 @@
+{
+  "schemaVersion": 1,
+  "id": "turtle-reproduce-gametest",
+  "version": "1.0.0",
+  "name": "Turtle Reproduce Game Tests",
+  "environment": "*",
+  "entrypoints": {
+    "fabric-gametest": [
+      "com.mr.gametest.TurtleNestingGameTests",
+      "com.mr.gametest.WetNestingGameTests"
+    ]
+  },
+  "depends": {
+    "turtle-reproduce": "*",
+    "fabric-gametest-api-v1": "*"
+  }
+}

src/main/java/com/mr/ai/NestingSiteFinder.java

@@ -0,0 +1,254 @@
+package com.mr.ai;
+
+import it.unimi.dsi.fastutil.longs.Long2DoubleOpenHashMap;
+import it.unimi.dsi.fastutil.longs.LongArrayList;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.SectionPos;
+import net.minecraft.tags.BlockTags;
+import net.minecraft.tags.FluidTags;
+import net.minecraft.world.entity.animal.turtle.Turtle;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.LevelReader;
+import net.minecraft.world.level.block.TurtleEggBlock;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.LevelChunkSection;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.material.FluidState;
+import net.minecraft.world.phys.Vec3;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * Finds dry nesting blocks beside nearby, exposed source water.
+ *
+ * <p>This class was rewritten for throughput. The scan is the hot path: one call
+ * covers 73 x 73 columns x 19 vertical steps, and a pregnant turtle re-runs it
+ * whenever it drifts more than four blocks from the previous search origin or
+ * exhausts its cached candidate list.
+ *
+ * <p>Every result-affecting rule is unchanged:
+ * <ul>
+ *   <li>the same box is visited (32 in X/Z for nests, plus a 4 block halo for
+ *       water, 8 up/down for nests, plus 1 for water);</li>
+ *   <li>the same conditions are tested, in the same order;</li>
+ *   <li>unloaded chunks are still skipped, and are still never loaded or
+ *       generated ({@code loadOrGenerate = false});</li>
+ *   <li>the candidate list is still ordered by the same comparator, which ends
+ *       in the block coordinates and therefore is a total order. Visit order no
+ *       longer matters, so the sort result is identical.</li>
+ * </ul>
+ *
+ * <p>What changed, and why it is equivalent:
+ * <ul>
+ *   <li>blocks are read through the chunk section that holds them instead of
+ *       {@code Level#getBlockState}, which re-resolves the chunk, the section
+ *       index and the build-height check on every single block. Sections that
+ *       {@code hasOnlyAir()} are skipped entirely: they cannot contribute water
+ *       or sand;</li>
+ *   <li>the same availability test as {@code Level#hasChunk} is used, but the
+ *       resolved chunk is kept for the section reads instead of being thrown
+ *       away and looked up again per block;</li>
+ *   <li>sand positions are collected as packed longs instead of thousands of
+ *       {@code BlockPos} objects, so a scan allocates no per-block garbage;</li>
+ *   <li>{@code isValidSite} hoists its loop invariants and remembers the last
+ *       chunk availability answer; the disk it walks spans at most four chunks,
+ *       so this only removes repeated lookups.</li>
+ * </ul>
+ */
+public final class NestingSiteFinder {
+    public static final int SEARCH_RADIUS = 32;
+    public static final int VERTICAL_SEARCH_RADIUS = 8;
+    public static final int WATER_RADIUS = 4;
+    public static final int WATER_VERTICAL_RADIUS = 1;
+
+    private static final Comparator<Candidate> CANDIDATE_ORDER = Comparator
+            .comparingDouble(Candidate::waterDistanceSquared)
+            .thenComparingDouble(Candidate::sandDistanceSquared)
+            .thenComparingInt(candidate -> candidate.sandPos().getX())
+            .thenComparingInt(candidate -> candidate.sandPos().getY())
+            .thenComparingInt(candidate -> candidate.sandPos().getZ());
+
+    private NestingSiteFinder() {
+    }
+
+    /**
+     * Searches a square extending 32 blocks in X/Z and 8 blocks in Y from the
+     * turtle. A four-block halo includes water beside nests at the boundary.
+     * The caller must check the turtle's collision box and navigation path.
+     */
+    public static List<Candidate> findCandidates(Turtle turtle) {
+        Level level = turtle.level();
+        BlockPos origin = turtle.blockPosition();
+        int originX = origin.getX();
+        int originY = origin.getY();
+        int originZ = origin.getZ();
+        int scanRadius = SEARCH_RADIUS + WATER_RADIUS;
+        int minY = Math.max(level.getMinY(), originY - VERTICAL_SEARCH_RADIUS - WATER_VERTICAL_RADIUS);
+        int maxY = Math.min(level.getMaxY() - 1, originY + VERTICAL_SEARCH_RADIUS + WATER_VERTICAL_RADIUS);
+        int nestMinX = originX - SEARCH_RADIUS;
+        int nestMaxX = originX + SEARCH_RADIUS;
+        int nestMinZ = originZ - SEARCH_RADIUS;
+        int nestMaxZ = originZ + SEARCH_RADIUS;
+        int nestMinY = originY - VERTICAL_SEARCH_RADIUS;
+        int nestMaxY = originY + VERTICAL_SEARCH_RADIUS;
+
+        BlockPos.MutableBlockPos cursor = new BlockPos.MutableBlockPos();
+        LongArrayList sandBlocks = new LongArrayList();
+        Long2DoubleOpenHashMap waterDistances = new Long2DoubleOpenHashMap();
+        waterDistances.defaultReturnValue(Double.POSITIVE_INFINITY);
+
+        // Read each block once, instead of repeatedly querying the world around
+        // every sand block. Unloaded chunks are never requested or generated.
+        if (minY <= maxY) {
+            Vec3 turtlePos = turtle.position();
+            int minSection = level.getSectionIndex(minY);
+            int maxSection = level.getSectionIndex(maxY);
+            for (int chunkX = (originX - scanRadius) >> 4; chunkX <= (originX + scanRadius) >> 4; chunkX++) {
+                int fromX = Math.max(originX - scanRadius, chunkX << 4);
+                int toX = Math.min(originX + scanRadius, (chunkX << 4) + 15);
+                for (int chunkZ = (originZ - scanRadius) >> 4; chunkZ <= (originZ + scanRadius) >> 4; chunkZ++) {
+                    // The same test Level#hasChunk performs, except the chunk is
+                    // kept: loadOrGenerate = false never loads or generates.
+                    ChunkAccess chunk = level.getChunk(chunkX, chunkZ, ChunkStatus.FULL, false);
+                    if (chunk == null) {
+                        continue;
+                    }
+                    int fromZ = Math.max(originZ - scanRadius, chunkZ << 4);
+                    int toZ = Math.min(originZ + scanRadius, (chunkZ << 4) + 15);
+                    LevelChunkSection[] sections = chunk.getSections();
+                    for (int sectionIndex = minSection; sectionIndex <= maxSection; sectionIndex++) {
+                        if (sectionIndex < 0 || sectionIndex >= sections.length) {
+                            continue;
+                        }
+                        LevelChunkSection section = sections[sectionIndex];
+                        // An all-air section holds neither water nor sand, so
+                        // skipping it reads no block the loops could have used.
+                        if (section == null || section.hasOnlyAir()) {
+                            continue;
+                        }
+                        int sectionMinY = SectionPos.sectionToBlockCoord(level.getMinSectionY() + sectionIndex);
+                        int fromY = Math.max(minY, sectionMinY);
+                        int toY = Math.min(maxY, sectionMinY + 15);
+                        boolean nestSection = fromY <= nestMaxY && toY >= nestMinY;
+                        for (int x = fromX; x <= toX; x++) {
+                            int localX = x & 15;
+                            boolean nestX = x >= nestMinX && x <= nestMaxX;
+                            for (int z = fromZ; z <= toZ; z++) {
+                                boolean inNestRange = nestSection && nestX && z >= nestMinZ && z <= nestMaxZ;
+                                int localZ = z & 15;
+                                for (int y = fromY; y <= toY; y++) {
+                                    BlockState state = section.getBlockState(localX, y & 15, localZ);
+                                    if (isExposedSourceWater(level, cursor, x, y, z, state)) {
+                                        cursor.set(x, y, z);
+                                        waterDistances.put(BlockPos.asLong(x, y, z),
+                                                cursor.distToCenterSqr(turtlePos));
+                                    }
+                                    if (inNestRange && y >= nestMinY && y <= nestMaxY
+                                            && state.is(BlockTags.SAND)
+                                            && level.isEmptyBlock(cursor.set(x, y + 1, z))) {
+                                        sandBlocks.add(BlockPos.asLong(x, y, z));
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        List<Candidate> candidates = new ArrayList<>();
+        if (waterDistances.isEmpty()) {
+            return candidates;
+        }
+        Vec3 turtlePos = turtle.position();
+        for (int index = 0; index < sandBlocks.size(); index++) {
+            long packedSand = sandBlocks.getLong(index);
+            int sandX = BlockPos.getX(packedSand);
+            int sandY = BlockPos.getY(packedSand);
+            int sandZ = BlockPos.getZ(packedSand);
+            double nearestWaterDistance = Double.POSITIVE_INFINITY;
+            for (int dx = -WATER_RADIUS; dx <= WATER_RADIUS; dx++) {
+                for (int dz = -WATER_RADIUS; dz <= WATER_RADIUS; dz++) {
+                    if (dx * dx + dz * dz > WATER_RADIUS * WATER_RADIUS) {
+                        continue;
+                    }
+                    for (int dy = -WATER_VERTICAL_RADIUS; dy <= WATER_VERTICAL_RADIUS; dy++) {
+                        long waterPosition = BlockPos.asLong(sandX + dx, sandY + dy, sandZ + dz);
+                        nearestWaterDistance = Math.min(nearestWaterDistance, waterDistances.get(waterPosition));
+                    }
+                }
+            }
+            if (Double.isFinite(nearestWaterDistance)) {
+                cursor.set(sandX, sandY, sandZ);
+                candidates.add(new Candidate(new BlockPos(sandX, sandY, sandZ), nearestWaterDistance,
+                        cursor.distToCenterSqr(turtlePos)));
+            }
+        }
+        candidates.sort(CANDIDATE_ORDER);
+        return candidates;
+    }
+
+    /** Rechecks a chosen nest, including changes to its sand, air, or water. */
+    public static boolean isValidSite(LevelReader level, BlockPos sandPos) {
+        if (!level.isInsideBuildHeight(sandPos) || !level.isInsideBuildHeight(sandPos.above())
+                || !level.hasChunkAt(sandPos)
+                || !TurtleEggBlock.isSand(level, sandPos)
+                || !level.isEmptyBlock(sandPos.above())) {
+            return false;
+        }
+        int sandX = sandPos.getX();
+        int sandY = sandPos.getY();
+        int sandZ = sandPos.getZ();
+        BlockPos.MutableBlockPos cursor = new BlockPos.MutableBlockPos();
+        int lastChunkX = Integer.MIN_VALUE;
+        int lastChunkZ = Integer.MIN_VALUE;
+        boolean lastChunkLoaded = false;
+        for (int dx = -WATER_RADIUS; dx <= WATER_RADIUS; dx++) {
+            for (int dz = -WATER_RADIUS; dz <= WATER_RADIUS; dz++) {
+                if (dx * dx + dz * dz > WATER_RADIUS * WATER_RADIUS) {
+                    continue;
+                }
+                int x = sandX + dx;
+                int z = sandZ + dz;
+                int chunkX = x >> 4;
+                int chunkZ = z >> 4;
+                // The disk above spans at most four chunks, so this only removes
+                // repeated queries for columns that share a chunk.
+                if (chunkX != lastChunkX || chunkZ != lastChunkZ) {
+                    lastChunkX = chunkX;
+                    lastChunkZ = chunkZ;
+                    lastChunkLoaded = level.hasChunk(chunkX, chunkZ);
+                }
+                if (!lastChunkLoaded) {
+                    continue;
+                }
+                for (int dy = -WATER_VERTICAL_RADIUS; dy <= WATER_VERTICAL_RADIUS; dy++) {
+                    int y = sandY + dy;
+                    cursor.set(x, y, z);
+                    if (level.isInsideBuildHeight(y) && level.isInsideBuildHeight(y + 1)
+                            && isExposedSourceWater(level, cursor, x, y, z, level.getBlockState(cursor))) {
+                        return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
+
+    private static boolean isExposedSourceWater(LevelReader level, BlockPos.MutableBlockPos cursor,
+                                                int x, int y, int z, BlockState state) {
+        // Requiring a liquid block excludes waterlogged fences, slabs and other
+        // solid blocks even though their fluid state may report source water.
+        if (!state.liquid()) {
+            return false;
+        }
+        FluidState fluid = state.getFluidState();
+        return fluid.is(FluidTags.WATER) && fluid.isSource() && level.isEmptyBlock(cursor.set(x, y + 1, z));
+    }
+
+    public record Candidate(BlockPos sandPos, double waterDistanceSquared, double sandDistanceSquared) {
+    }
+}

src/main/java/com/mr/mixin/PathNavigationAccessor.java

@@ -0,0 +1,11 @@
+package com.mr.mixin;
+
+import net.minecraft.world.entity.ai.navigation.PathNavigation;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Accessor;
+
+@Mixin(PathNavigation.class)
+public interface PathNavigationAccessor {
+	@Accessor("maxVisitedNodesMultiplier")
+	float turtleReproduce$getMaxVisitedNodesMultiplier();
+}

src/main/java/com/mr/mixin/TurtleAccessor.java

@@ -0,0 +1,22 @@
+package com.mr.mixin;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.entity.animal.turtle.Turtle;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Accessor;
+import org.spongepowered.asm.mixin.gen.Invoker;
+
+@Mixin(Turtle.class)
+public interface TurtleAccessor {
+	@Invoker("setHasEgg")
+	void turtleReproduce$setHasEgg(boolean hasEgg);
+
+	@Invoker("setLayingEgg")
+	void turtleReproduce$setLayingEgg(boolean layingEgg);
+
+	@Accessor("homePos")
+	BlockPos turtleReproduce$getHomePos();
+
+	@Accessor("goingHome")
+	boolean turtleReproduce$isGoingHome();
+}

src/main/java/com/mr/mixin/TurtleGoHomeGoalMixin.java

@@ -0,0 +1,32 @@
+package com.mr.mixin;
+
+import net.minecraft.world.entity.animal.turtle.Turtle;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(targets = "net.minecraft.world.entity.animal.turtle.Turtle$TurtleGoHomeGoal")
+public abstract class TurtleGoHomeGoalMixin {
+	@Shadow @Final
+	private Turtle turtle;
+
+	// This goal has no MOVE flag, so priority alone cannot stop it fighting nesting.
+	@Inject(method = {"canUse", "canContinueToUse"}, at = @At("HEAD"), cancellable = true)
+	private void turtleReproduce$stayLocalWhileCarryingEggs(CallbackInfoReturnable<Boolean> cir) {
+		if (this.turtle.hasEgg()) {
+			cir.setReturnValue(false);
+		}
+	}
+
+	@Inject(method = "stop", at = @At("TAIL"))
+	private void turtleReproduce$discardOldHomeRoute(CallbackInfo ci) {
+		if (this.turtle.hasEgg()) {
+			// The vanilla stop only clears goingHome, leaving its last route active.
+			this.turtle.getNavigation().stop();
+		}
+	}
+}

src/main/java/com/mr/mixin/TurtleLayEggGoalMixin.java

@@ -0,0 +1,129 @@
+package com.mr.mixin;
+
+import com.mr.ai.NestingSiteFinder;
+import java.util.List;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.entity.PathfinderMob;
+import net.minecraft.world.entity.ai.goal.MoveToBlockGoal;
+import net.minecraft.world.entity.ai.navigation.PathNavigation;
+import net.minecraft.world.entity.animal.turtle.Turtle;
+import net.minecraft.world.level.LevelReader;
+import net.minecraft.world.level.pathfinder.Path;
+import net.minecraft.world.phys.AABB;
+import net.minecraft.world.phys.Vec3;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(targets = "net.minecraft.world.entity.animal.turtle.Turtle$TurtleLayEggGoal")
+public abstract class TurtleLayEggGoalMixin extends MoveToBlockGoal {
+	@Unique private static final int PATH_SEARCH_RANGE = 48;
+	@Unique private static final int PATH_ATTEMPTS_PER_CHECK = 16;
+
+	@Shadow @Final
+	private Turtle turtle;
+	@Unique private List<NestingSiteFinder.Candidate> turtleReproduce$candidates = List.of();
+	@Unique private int turtleReproduce$candidateIndex;
+	@Unique private BlockPos turtleReproduce$searchOrigin = BlockPos.ZERO;
+	@Unique private Path turtleReproduce$nestingPath;
+
+	protected TurtleLayEggGoalMixin(PathfinderMob mob, double speed, int range) {
+		super(mob, speed, range);
+	}
+
+	@Inject(method = "canUse", at = @At("HEAD"), cancellable = true)
+	private void turtleReproduce$findLocalShore(CallbackInfoReturnable<Boolean> cir) {
+		cir.setReturnValue(this.turtle.hasEgg() && !this.turtle.isBaby() && super.canUse());
+	}
+
+	@Inject(method = "canContinueToUse", at = @At("HEAD"), cancellable = true)
+	private void turtleReproduce$continueAwayFromHome(CallbackInfoReturnable<Boolean> cir) {
+		cir.setReturnValue(this.turtle.hasEgg() && super.canContinueToUse());
+	}
+
+	@Inject(method = "isValidTarget", at = @At("HEAD"), cancellable = true)
+	private void turtleReproduce$requireDrySandNearWater(LevelReader level, BlockPos pos,
+			CallbackInfoReturnable<Boolean> cir) {
+		cir.setReturnValue(NestingSiteFinder.isValidSite(level, pos));
+	}
+
+	@Override
+	protected boolean findNearestBlock() {
+		if (this.turtleReproduce$candidateIndex >= this.turtleReproduce$candidates.size()
+				|| this.turtle.blockPosition().distSqr(this.turtleReproduce$searchOrigin) > 16.0) {
+			this.turtleReproduce$candidates = NestingSiteFinder.findCandidates(this.turtle);
+			this.turtleReproduce$candidateIndex = 0;
+			this.turtleReproduce$searchOrigin = this.turtle.blockPosition();
+		}
+
+		// Spread expensive path checks over AI updates when a shore is inaccessible.
+		int attempts = 0;
+		while (this.turtleReproduce$candidateIndex < this.turtleReproduce$candidates.size()
+				&& attempts++ < PATH_ATTEMPTS_PER_CHECK) {
+			BlockPos sand = this.turtleReproduce$candidates.get(this.turtleReproduce$candidateIndex++).sandPos();
+			if (!this.turtle.isWithinHome(sand) || !NestingSiteFinder.isValidSite(this.turtle.level(), sand)) {
+				continue;
+			}
+			Vec3 destination = Vec3.atBottomCenterOf(sand.above());
+			AABB destinationBounds = this.turtle.getBoundingBox().move(destination.subtract(this.turtle.position()));
+			// Adult turtles are wider than one block. An air block alone does not
+			// guarantee that their body is clear of adjacent water or walls.
+			if (!this.turtle.level().noCollision(this.turtle, destinationBounds)
+					|| this.turtle.level().containsAnyLiquid(destinationBounds.deflate(0.001))) {
+				continue;
+			}
+			Path path = this.turtleReproduce$createNestingPath(sand.above());
+			if (path != null && path.canReach()) {
+				this.blockPos = sand;
+				this.turtleReproduce$nestingPath = path;
+				this.turtleReproduce$candidates = List.of();
+				return true;
+			}
+		}
+		if (this.turtleReproduce$candidateIndex < this.turtleReproduce$candidates.size()) {
+			this.nextStartTick = 1;
+		}
+		return false;
+	}
+
+	@Unique
+	private Path turtleReproduce$createNestingPath(BlockPos destination) {
+		PathNavigation navigation = this.turtle.getNavigation();
+		float previousMultiplier = ((PathNavigationAccessor) navigation).turtleReproduce$getMaxVisitedNodesMultiplier();
+		// A larger distance alone leaves vanilla's small node budget unchanged,
+		// incorrectly rejecting shores that require a detour around an obstacle.
+		navigation.setMaxVisitedNodesMultiplier(Math.max(previousMultiplier, 8.0F));
+		try {
+			return navigation.createPath(destination, 0, PATH_SEARCH_RANGE);
+		} finally {
+			navigation.setMaxVisitedNodesMultiplier(previousMultiplier);
+		}
+	}
+
+	@Override
+	protected void moveMobToBlock() {
+		this.turtle.getNavigation().moveTo(this.turtleReproduce$nestingPath, this.speedModifier);
+	}
+
+	@Inject(method = "tick", at = @At("TAIL"))
+	private void turtleReproduce$retryLongerPath(CallbackInfo ci) {
+		if (!this.isReachedTarget() && this.tryTicks % 40 == 0 && this.turtle.getNavigation().isDone()) {
+			this.turtleReproduce$nestingPath = this.turtleReproduce$createNestingPath(this.blockPos.above());
+			this.moveMobToBlock();
+		}
+	}
+
+	@Override
+	public void stop() {
+		super.stop();
+		this.turtle.getNavigation().stop();
+		((TurtleAccessor) this.turtle).turtleReproduce$setLayingEgg(false);
+		this.turtleReproduce$nestingPath = null;
+		this.turtleReproduce$candidates = List.of();
+	}
+}

src/main/kotlin/com/mr/TurtleReproduce.kt

@@ -0,0 +1,18 @@
+package com.mr
+
+import net.fabricmc.api.ModInitializer
+import net.minecraft.resources.Identifier
+import org.slf4j.LoggerFactory
+
+object TurtleReproduce : ModInitializer {
+	const val MOD_ID: String = "turtle-reproduce"
+
+	private val LOGGER = LoggerFactory.getLogger(MOD_ID)
+
+	override fun onInitialize() {
+		LOGGER.info("Turtle Reproduce: local waterside nesting enabled")
+	}
+
+	fun id(path: String): Identifier
+		= Identifier.fromNamespaceAndPath(MOD_ID, path)
+}

src/main/resources/fabric.mod.json

@@ -0,0 +1,43 @@
+{
+	"schemaVersion": 1,
+	"id": "turtle-reproduce",
+	"version": "${version}",
+	"name": "Turtle-Reproduce",
+	"description": "Turtles lay eggs on reachable sand near the closest local water source instead of returning to their birthplace.",
+	"authors": [
+		"Me!"
+	],
+	"license": "CC0-1.0",
+	"icon": "assets/turtle-reproduce/icon.png",
+	"environment": "*",
+	"entrypoints": {
+		"main": [
+			{
+				"value": "com.mr.TurtleReproduce",
+				"adapter": "kotlin"
+			}
+		],
+		"client": [
+			{
+				"value": "com.mr.client.TurtleReproduceClient",
+				"adapter": "kotlin"
+			}
+		],
+		"fabric-datagen": [
+			{
+				"value": "com.mr.client.TurtleReproduceDataGenerator",
+				"adapter": "kotlin"
+			}
+		]
+	},
+	"mixins": [
+		"turtle-reproduce.mixins.json"
+	],
+	"depends": {
+		"fabricloader": ">=0.19.5",
+		"minecraft": "~26.1.2",
+		"java": ">=25",
+		"fabric-api": "*",
+		"fabric-language-kotlin": "*"
+	}
+}

src/main/resources/turtle-reproduce.mixins.json

@@ -0,0 +1,17 @@
+{
+	"required": true,
+	"package": "com.mr.mixin",
+	"compatibilityLevel": "JAVA_25",
+	"mixins": [
+		"PathNavigationAccessor",
+		"TurtleAccessor",
+		"TurtleGoHomeGoalMixin",
+		"TurtleLayEggGoalMixin"
+	],
+	"injectors": {
+		"defaultRequire": 1
+	},
+	"overwrites": {
+		"requireAnnotations": true
+	}
+}