Match base entity fall accumulation and landing callback order

2026-11-07 02:56:17 -10:00 · 2026-10-07 01:01:15 +02:00
1 parent e39e0b56c0
commit 38d60eef9e
@@ -0,0 +1,215 @@
+{
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+    "crates/horizon-world/src/worldgen/bulk_section.rs": "eecf61532d7793f853884c5a18a7f436a59835c7b13d3ec9075804511553c9ba",
+    "crates/horizon-world/src/worldgen/carver/canyon.rs": "509c4d5a9d689849e98e894ab14a9fbf82d10707d38e9cc688ded3c4778df3e2",
+    "crates/horizon-world/src/worldgen/carver/generation.rs": "a4498d0d1457536de3922a08e9c40ccce8d2ef9cc263801c15a412327513c098",
+    "crates/horizon-world/src/worldgen/carver.rs": "46b251e28225fe1250de38f49dec5dacda4e2c4ba1e556e21e6d1e14e2651fc3",
+    "crates/horizon-world/src/worldgen/carving.rs": "4e77d4e5c4a0ca55ca3563b9bdf6f379342e0bdf9d019d60f7bc57ce4afb5fbd",
+    "crates/horizon-world/src/worldgen/chorus_plant.rs": "29224c164ede919e280a65a68f155c873e2c8fd0aa7d7e244d8fa9e468760250",
+    "crates/horizon-world/src/worldgen/climate/codec.rs": "d567adeb5d837816fca69102db51d790f71aec1b51c09298230d24612e400a14",
+    "crates/horizon-world/src/worldgen/climate/index.rs": "c5ce61679a5f0e0f2f0af2a373424effa124d0cce8250609eff38b7034650756",
+    "crates/horizon-world/src/worldgen/climate.rs": "1b9ad44407f40aee4c1cd5357a5c9c443c1b105728f01cf5c644072f99f8357e",
+    "crates/horizon-world/src/worldgen/decoration.rs": "75a79b20b21e133816e729f16e758be6165d0db18a64bfbd5fd3618325a2adf3",
+    "crates/horizon-world/src/worldgen/delta.rs": "c2bf49ddf3231d28c109e68871429bc13d76a7bebe14eb33e84aa856bdd66145",
+    "crates/horizon-world/src/worldgen/density.rs": "65a98c156a290a6b374ef670d28cd5dfbe0aa93171824d1bbd96422536273f84",
+    "crates/horizon-world/src/worldgen/disk.rs": "6f8f9e059755af44c9bfa1b91eba54a7d13fad811dce31717c5502d7f6df33d7",
+    "crates/horizon-world/src/worldgen/end_gateway.rs": "f53fde77d6a36a525cd15d890003b2c129d0689a4cbfa2cf443a0c2e3acae040",
+    "crates/horizon-world/src/worldgen/end_podium.rs": "8f6d0d6d60ff0fde63de5781e867239db321f82cf12639f0537d410a3731ee1d",
+    "crates/horizon-world/src/worldgen/feature.rs": "40500af71ee6628dfb27518262d99f08d0383ae6c7b9397452feef0c213eadd9",
+    "crates/horizon-world/src/worldgen/feature_catalog.rs": "efc7b17b227e71622ef34108be9abd010f5675b68ea0409fcab82581d9aab88a",
+    "crates/horizon-world/src/worldgen/feature_graph.rs": "da132fca9fdafb0d89a917d5f4b68c60b70fb33cadf948a107da0e35d83dcd91",
+    "crates/horizon-world/src/worldgen/feature_region.rs": "df0ff142a461cafa9a3b42b949ad3376887f2be8d4ea5cc794a3ed2e977bb499",
+    "crates/horizon-world/src/worldgen/feature_sort.rs": "3488a093dfe1321aaa29d8a30cfb115d8e666a81bf195514e87b170de626835c",
+    "crates/horizon-world/src/worldgen/fluid_predicate.rs": "64197c9e63bebf1ce04bc280bfe980bb6c1b9aa887ca5cded904aeb0d9ae6c46",
+    "crates/horizon-world/src/worldgen/height_provider.rs": "368d4dc119854742a045c4a717679c921456da681fc5f71aa9b37102d6f33b47",
+    "crates/horizon-world/src/worldgen/material_condition/codec.rs": "09b909bc384472f76d163c8069ec6b507c7d5c6a028a36d5e0e3df20deff7b3b",
+    "crates/horizon-world/src/worldgen/material_condition/density.rs": "df9d0761e978e5010663ae8b44f2d6c1ecb4907331e333bdb6a2b487c1e107de",
+    "crates/horizon-world/src/worldgen/material_condition/library.rs": "a55534c5da97575a819af5a7dc0dbec9069993fa8b2619c6c9d5576946e683fa",
+    "crates/horizon-world/src/worldgen/material_condition/noise.rs": "ffb59cc6be2275d7a5621bf7d768527e74a8326ed7ad78618746711540921675",
+    "crates/horizon-world/src/worldgen/material_condition/rule.rs": "fed643352efbcb1f68f29b6241896617db889fc7c577a6247564e01922fec1fe",
+    "crates/horizon-world/src/worldgen/material_condition.rs": "d638dcb8cbcb5da20b3cb29602b0ae6a86c4fdf9d8c0fb725de8ec5fc108717e",
+    "crates/horizon-world/src/worldgen/material_extensions.rs": "ab806eb679d5116e1aebb64fca70e1499ae71f83c9507a8cb4c3201c2b1bf037",
+    "crates/horizon-world/src/worldgen/material_stage.rs": "698cbc786eff13c246e2bc2ea062401918cd4265899fbc3d53abc87e45a8e7a1",
+    "crates/horizon-world/src/worldgen/material_surface.rs": "5d37b90099df3d6da0845dab164e71469fb287019c2ee74bc6714f3b9d6d6d5b",
+    "crates/horizon-world/src/worldgen/ore_feature.rs": "83b89fd3be691c5412c0215b6abefdcaa44119a05aa41217e061970eb7e12ebd",
+    "crates/horizon-world/src/worldgen/placement/chain.rs": "9218399b4d3757f7bbc550d7729a7201f32a1c83a7030865e0c12aab8a80d116",
+    "crates/horizon-world/src/worldgen/placement/context.rs": "a278304795136677ad4b4933ea50c972b9729a1c671c03fa309c193e224b1fd6",
+    "crates/horizon-world/src/worldgen/placement/layer.rs": "a0f5ca776f33f9d4f72b8fdcd163426152e5e43cb4a7572fc1d4fc57bf965de1",
+    "crates/horizon-world/src/worldgen/placement.rs": "b0397e5818fae84358546193a95f84bcb0b5bffafce909e6fcb3386179ee8023",
+    "crates/horizon-world/src/worldgen/replace_blobs.rs": "bf3377d86d2570cd15288ba69dde64a2cf67c5bcbb9a31d0c23421964af74afa",
+    "crates/horizon-world/src/worldgen/router.rs": "2cee7cf15a0d2ada12be6b39d83e78177fd3033922e4f4cce87a64073cec2847",
+    "crates/horizon-world/src/worldgen/rule_test.rs": "d1662ec492489ebaa4b87e20f9a8c809dcf3a223a151211bd65ec241a63692fc",
+    "crates/horizon-world/src/worldgen/settings.rs": "a8fe87752e1982ef11cb67f8d80d8e3428b2c27db178044cb425ba803e689e59",
+    "crates/horizon-world/src/worldgen/simple_block.rs": "9ba1a88d5db4925f8c37366557887f776c805f9a6444781615b5dbaff52e92a4",
+    "crates/horizon-world/src/worldgen/snow_freeze.rs": "9040be3d5c7f8f0fd812d2df45e154bf8a9eeef038530b83fa4159d246eac35f",
+    "crates/horizon-world/src/worldgen/speleothem.rs": "c71651c1c97818a8a85863e14414d6139ea3bdeb897fa422043bcc1499d99aae",
+    "crates/horizon-world/src/worldgen/spike.rs": "eacf0d9d3d2bc3d4bcf62bc87555f90031138236a5bfef0eb5270204f7c2a4fc",
+    "crates/horizon-world/src/worldgen/spring.rs": "830849e9b89fcdf09e9b06fbefdcdebe3c8c3f82804f60b8bd5de04ba303cb62",
+    "crates/horizon-world/src/worldgen/state_provider/catalog.rs": "c8687e15a4887a9200c8d365857d801efaa8f90e669eee3e600a1db4905119eb",
+    "crates/horizon-world/src/worldgen/state_provider/noise.rs": "7ee369c2a032e5620cb9bdf9ee7adad1f70870fb0a27efb7b7c514d92f83491f",
+    "crates/horizon-world/src/worldgen/state_provider/properties.rs": "9909139aaca1dc4f743957257fadaa9d423d21fa401fa9abc050505f79365139",
+    "crates/horizon-world/src/worldgen/state_provider.rs": "be29ada818826a90afe01ab60916360fdfc4cbde5af15c9359cd56b1f1f7b156",
+    "crates/horizon-world/src/worldgen/tags.rs": "d35ded93fe6e95ea045cadcf4925e656dc34ef832b742179b9ad0cc49f902f31",
+    "crates/horizon-world/src/worldgen/terrain.rs": "fd1f2e0afc15daf66f484ea40a1f2b7013650bda0941b23c64c81ee9f79cb673",
+    "crates/horizon-world/src/worldgen/underwater_magma.rs": "7317e40af5ee5a9780f90ce358fa5d3e7f5b3d513b731df6ff97754d9c2a0154",
+    "crates/horizon-world/src/worldgen/value_provider.rs": "3358b563db8cb0bc8a9cfbbe2b8b3e70941cd2d37a0b519fbb6545f8d0dcbb69",
+    "crates/horizon-world/src/worldgen/vines.rs": "ee9b79b65012bd86a838241d2ef708680f7fe8eafc8aa656dae9cf2abf3c6418",
+    "crates/horizon-world/src/worldgen/weighted.rs": "839840aae25302933bbd97a81a2336330e2d03a0ad1684e1e16ac769ed408e6b",
+    "crates/horizon-world/src/worldgen/write_zone.rs": "8e17a179764d3f68c05882aef35f6810c28a0000f9a83e58bd6030660b76e64e",
+    "crates/horizon-world/src/worldgen.rs": "e8e9f099ee1fcec8eedce31805d676d3f89c18e84f494a147ffcbfee23d3d54f",
+    "crates/horizon-world/examples/fall_damage_fixture.rs": "98a4dcdf23b2666bf46bac38513c84a83fdc4de1c014b01b59f678fe3f82a560"
+  },
+  "fixtures_sha256": {
+    ".local/rust-fall-damage-parity/inputs.txt": "4981d3a5a00c29308102c51f8dd093a9f37900501ff13fe4c61abfad1374ad2b"
+  },
+  "rust_output_sha256": "3d272db7c9407a6984e855b9126bf877188624edeb00f123b9ba145707db89de",
+  "references": [
+    {
+      "side": "client",
+      "jar_sha256": "4508d006323f24fa02876310c192d739af56516eb259000ac50f0909a68c9a2d",
+      "output_sha256": "3d272db7c9407a6984e855b9126bf877188624edeb00f123b9ba145707db89de",
+      "matched_output_lines": 44566
+    },
+    {
+      "side": "server",
+      "jar_sha256": "a362163eec5d1612d520772bc16e5b39c09e3b234fdc045f56bf544284ee8ae6",
+      "output_sha256": "3d272db7c9407a6984e855b9126bf877188624edeb00f123b9ba145707db89de",
+      "matched_output_lines": 44566
+    }
+  ],
+  "scope": "Actual base Entity.checkFallDamage with controlled water state, block landing callback, supporting-block lookup, HIT_GROUND emission and reset. Compares float-narrowed downward displacement accumulation, grounded branches, state/position/support mutations during landing, callback order, nonfinite arithmetic and partial state after failures. LivingEntity fluid updates/particles, registered Block.fallOn behavior, health/damage/attributes and the full movement lifecycle are not established by this scoped check."
+}
@@ -0,0 +1,146 @@
+use horizon_core::{geometry::Vec3, position::BlockPos};
+use horizon_world::fall_damage::{FallDamageWorld, check_fall_damage};
+use serde_json::Value;
+use std::{
+    fs,
+    io::{self, Write},
+    path::Path,
+};
+fn number(v: &Value) -> f64 {
+    f64::from_bits(u64::from_str_radix(v.as_str().unwrap(), 16).unwrap())
+}
+fn bits(v: f64) -> u64 {
+    if v.is_nan() {
+        0x7ff8000000000000
+    } else {
+        v.to_bits()
+    }
+}
+fn support(v: &Value) -> Option<BlockPos> {
+    if v.is_null() {
+        None
+    } else {
+        Some(BlockPos::new(
+            v[0].as_i64().unwrap() as i32,
+            v[1].as_i64().unwrap() as i32,
+            v[2].as_i64().unwrap() as i32,
+        ))
+    }
+}
+struct World<'a> {
+    input: &'a Value,
+    out: &'a mut dyn Write,
+    calls: i64,
+    fall: f64,
+    position: Vec3,
+    support: Option<BlockPos>,
+}
+impl World<'_> {
+    fn query(&mut self, text: String) -> io::Result<()> {
+        writeln!(self.out, "{text}")?;
+        let call = self.calls;
+        self.calls += 1;
+        if call == self.input["fail"].as_i64().unwrap() {
+            Err(io::Error::other("injected fall query failure"))
+        } else {
+            Ok(())
+        }
+    }
+}
+impl FallDamageWorld for World<'_> {
+    type Error = io::Error;
+    type State = u8;
+    fn is_in_water(&mut self) -> io::Result<bool> {
+        self.query("water".into())?;
+        Ok(self.input["water"].as_bool().unwrap())
+    }
+    fn fall_distance(&self) -> f64 {
+        self.fall
+    }
+    fn set_fall_distance(&mut self, v: f64) {
+        self.fall = v;
+    }
+    fn fall_on(&mut self, _: u8, p: BlockPos, distance: f64) -> io::Result<()> {
+        self.query(format!(
+            "fall-on {} {} {} {:016x}",
+            p.x,
+            p.y,
+            p.z,
+            bits(distance)
+        ))?;
+        if self.input["mutate"].as_bool().unwrap() {
+            self.fall = 17.25;
+            self.position = Vec3::new(17.0, 18.0, 19.0);
+            self.support = support(&self.input["after_support"]);
+        }
+        Ok(())
+    }
+    fn position(&self) -> Vec3 {
+        self.position
+    }
+    fn supporting_block(&self) -> Option<BlockPos> {
+        self.support
+    }
+    fn block_state(&mut self, p: BlockPos) -> io::Result<u8> {
+        self.query(format!("state {} {} {}", p.x, p.y, p.z))?;
+        Ok(1)
+    }
+    fn hit_ground(&mut self, p: Vec3, s: u8) -> io::Result<()> {
+        self.query(format!(
+            "hit-ground {:016x} {:016x} {:016x} {}",
+            bits(p.x),
+            bits(p.y),
+            bits(p.z),
+            if s == 1 { "queried" } else { "input" }
+        ))
+    }
+    fn reset_fall_distance(&mut self) -> io::Result<()> {
+        self.query("reset".into())?;
+        self.fall = 0.0;
+        Ok(())
+    }
+}
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let arg = std::env::args().nth(1).expect("private fixture directory");
+    let dir = Path::new(&arg);
+    let mut out = io::BufWriter::new(fs::File::create(dir.join("rust.txt"))?);
+    for line in fs::read_to_string(dir.join("inputs.txt"))?.lines() {
+        let f: Value = serde_json::from_str(line)?;
+        let mut world = World {
+            input: &f,
+            out: &mut out,
+            calls: 0,
+            fall: number(&f["fall"]),
+            position: Vec3::new(0.3, 1.5, -0.3),
+            support: support(&f["support"]),
+        };
+        let result = check_fall_damage(
+            &mut world,
+            number(&f["dy"]),
+            f["ground"].as_bool().unwrap(),
+            0,
+            BlockPos::new(3, 4, 5),
+        );
+        writeln!(
+            world.out,
+            "result {}",
+            if result.is_ok() { "ok" } else { "error" }
+        )?;
+        let p = world.position;
+        writeln!(
+            world.out,
+            "final {:016x} {:016x} {:016x} {:016x}",
+            bits(world.fall),
+            bits(p.x),
+            bits(p.y),
+            bits(p.z)
+        )?;
+        if let Some(p) = world.support {
+            writeln!(world.out, "support {} {} {}", p.x, p.y, p.z)?;
+        } else {
+            writeln!(world.out, "support none")?;
+        }
+        writeln!(world.out, "queries {}", world.calls)?;
+    }
+    Ok(())
+}
@@ -0,0 +1,49 @@
+//! Base Entity fall-distance accumulation and landing callback ordering.
+use horizon_core::{geometry::Vec3, position::BlockPos};
+
+pub trait FallDamageWorld {
+    type Error;
+    type State: Copy;
+    fn is_in_water(&mut self) -> Result<bool, Self::Error>;
+    fn fall_distance(&self) -> f64;
+    fn set_fall_distance(&mut self, distance: f64);
+    fn fall_on(
+        &mut self,
+        state: Self::State,
+        position: BlockPos,
+        distance: f64,
+    ) -> Result<(), Self::Error>;
+    fn position(&self) -> Vec3;
+    fn supporting_block(&self) -> Option<BlockPos>;
+    fn block_state(&mut self, position: BlockPos) -> Result<Self::State, Self::Error>;
+    fn hit_ground(&mut self, position: Vec3, state: Self::State) -> Result<(), Self::Error>;
+    fn reset_fall_distance(&mut self) -> Result<(), Self::Error>;
+}
+/// LivingEntity's fluid update, landing particles and other overrides wrap this
+/// base method separately. Errors preserve prior field changes and callbacks.
+pub fn check_fall_damage<W: FallDamageWorld>(
+    world: &mut W,
+    dy: f64,
+    on_ground: bool,
+    state: W::State,
+    position: BlockPos,
+) -> Result<(), W::Error> {
+    if !world.is_in_water()? && dy < 0.0 {
+        world.set_fall_distance(world.fall_distance() - f64::from(dy as f32));
+    }
+    if on_ground {
+        if world.fall_distance() > 0.0 {
+            world.fall_on(state, position, world.fall_distance())?;
+            // Landing callbacks may move the entity or replace its support.
+            let position = world.position();
+            let state = if let Some(support) = world.supporting_block() {
+                world.block_state(support)?
+            } else {
+                state
+            };
+            world.hit_ground(position, state)?;
+        }
+        world.reset_fall_distance()?;
+    }
+    Ok(())
+}
@@ -18,6 +18,7 @@ pub mod dynamic_support;
 pub mod edge_backoff;
 pub mod entity_collision;
 pub mod entity_obstruction;
+pub mod fall_damage;
 pub mod fluid;
 pub mod ground_support;
 pub mod heightmap;
@@ -654,3 +654,18 @@ The shared fixture now supports player probes alongside direct movement and
 collision checks; workspace Clippy passes. Entity lists, border applicability and
 collision contexts remain controlled snapshots. A complete player movement/travel
 loop and playable client remain pending.
+
+
+`check_fall_damage` now implements base-entity fall-distance accumulation and
+landing order. Downward displacement narrows to float before being subtracted
+from the double fall distance. Grounded landings call the block, read the
+possibly changed position/support, emit the ground event and reset fall distance.
+Errors preserve completed field writes and callback effects.
+
+`python3 tools/test_fall_damage_parity.py` runs actual `Entity.checkFallDamage`
+with controlled water, landing and event providers. The
+[base fall report](../benchmarks/rust-fall-damage-2026-10-07/scoped-parity.json)
+records **44,566 matching lines per JAR**, including nonfinite arithmetic, float
+underflow, callback mutations and failures at every boundary. Workspace Clippy
+passes. Living-entity fluid/particle behavior, registered block landing effects,
+health/damage and full movement remain pending.
@@ -0,0 +1,53 @@
+package dev.horizonlab.parity;
+import com.google.gson.*;
+import java.io.*;
+import java.lang.reflect.*;
+import java.nio.file.*;
+import java.util.*;
+import net.minecraft.core.*;
+import net.minecraft.world.entity.*;
+import net.minecraft.world.level.*;
+import net.minecraft.world.level.block.*;
+import net.minecraft.world.level.block.state.*;
+import net.minecraft.world.level.gameevent.*;
+import net.minecraft.world.phys.Vec3;
+/** Actual base Entity checkFallDamage with traced landing callbacks and mutations. */
+public final class VanillaFallDamageOracle {
+    static final class Stop extends RuntimeException {}
+    static double number(JsonElement v){return Double.longBitsToDouble(Long.parseUnsignedLong(v.getAsString(),16));}
+    static Optional<BlockPos> support(JsonElement value){if(value.isJsonNull())return Optional.empty();var a=value.getAsJsonArray();return Optional.of(new BlockPos(a.get(0).getAsInt(),a.get(1).getAsInt(),a.get(2).getAsInt()));}
+    static Field positionField,supportField;
+    static final class Data {
+        JsonObject input;PrintWriter out;int calls;Actor actor;
+        void query(String text){out.println(text);if(calls++==input.get("fail").getAsInt())throw new Stop();}
+        void mutate() {if(input.get("mutate").getAsBoolean()){try{actor.fallDistance=17.25;positionField.set(actor,new Vec3(17,18,19));supportField.set(actor,support(input.get("after_support")));}catch(ReflectiveOperationException e){throw new AssertionError(e);}}}
+    }
+    static final class FallBlock extends Block {
+        Data d;FallBlock(){super(BlockBehaviour.Properties.of());}
+        @Override public void fallOn(net.minecraft.world.level.Level level,BlockState state,BlockPos p,Entity entity,double distance){d.query(String.format("fall-on %d %d %d %016x",p.getX(),p.getY(),p.getZ(),Double.doubleToLongBits(distance)));d.mutate();}
+    }
+    static final class State extends BlockState {Block block;State(){super(null,null,null);}@Override public Block getBlock(){return block;}}
+    static final class Level extends net.minecraft.server.level.ServerLevel {
+        Data d;BlockState queried;
+        private Level(){super(null,null,null,null,null,null,false,0L,List.of(),false);}
+        @Override public BlockState getBlockState(BlockPos p){d.query("state "+p.getX()+" "+p.getY()+" "+p.getZ());return queried;}
+        @Override public void gameEvent(Holder<GameEvent> event,Vec3 p,GameEvent.Context context){if(event!=GameEvent.HIT_GROUND)throw new AssertionError(event);d.query(String.format("hit-ground %016x %016x %016x %s",Double.doubleToLongBits(p.x),Double.doubleToLongBits(p.y),Double.doubleToLongBits(p.z),context.affectedState()==queried?"queried":"input"));}
+    }
+    static final class Actor extends Marker {
+        Data d;Actor(){super(null,null);}void configure(Level level){setLevel(level);}
+        @Override public boolean isInWater(){d.query("water");return d.input.get("water").getAsBoolean();}
+        @Override public void resetFallDistance(){d.query("reset");super.resetFallDistance();}
+        void check(double dy,boolean ground,BlockState state,BlockPos p){checkFallDamage(dy,ground,state,p);}
+    }
+    public static void main(String[] args)throws Exception {
+        net.minecraft.SharedConstants.tryDetectVersion();net.minecraft.server.Bootstrap.bootStrap();
+        var allocator=Class.forName("sun.misc.Unsafe");var field=allocator.getDeclaredField("theUnsafe");field.setAccessible(true);var unsafe=field.get(null);var allocate=allocator.getMethod("allocateInstance",Class.class);positionField=Entity.class.getDeclaredField("position");positionField.setAccessible(true);supportField=Entity.class.getDeclaredField("mainSupportingBlockPos");supportField.setAccessible(true);Path dir=Path.of(args[1]);
+        try(var out=new PrintWriter(Files.newBufferedWriter(dir.resolve(args[0]+".txt")));var lines=Files.lines(dir.resolve("inputs.txt"))){
+            for(var line:(Iterable<String>)lines::iterator){
+                var f=JsonParser.parseString(line).getAsJsonObject();var d=new Data();d.input=f;d.out=out;var level=(Level)allocate.invoke(unsafe,Level.class);level.d=d;level.queried=Blocks.STONE.defaultBlockState();var entity=(Actor)allocate.invoke(unsafe,Actor.class);entity.d=d;d.actor=entity;entity.configure(level);entity.fallDistance=number(f.get("fall"));positionField.set(entity,new Vec3(.3,1.5,-.3));supportField.set(entity,support(f.get("support")));var block=(FallBlock)allocate.invoke(unsafe,FallBlock.class);block.d=d;var state=(State)allocate.invoke(unsafe,State.class);state.block=block;
+                try{entity.check(number(f.get("dy")),f.get("ground").getAsBoolean(),state,new BlockPos(3,4,5));out.println("result ok");}catch(Stop error){out.println("result error");}
+                var p=(Vec3)positionField.get(entity);out.printf("final %016x %016x %016x %016x%n",Double.doubleToLongBits(entity.fallDistance),Double.doubleToLongBits(p.x),Double.doubleToLongBits(p.y),Double.doubleToLongBits(p.z));var selected=(Optional<?>)supportField.get(entity);if(selected.isEmpty())out.println("support none");else{var pos=(BlockPos)selected.get();out.println("support "+pos.getX()+" "+pos.getY()+" "+pos.getZ());}out.println("queries "+d.calls);
+            }
+        }
+    }
+}
@@ -0,0 +1,73 @@
+#!/usr/bin/env python3
+"""Compare base Entity fall accumulation and landing callbacks with vanilla."""
+import argparse
+import json
+import os
+from pathlib import Path
+import platform
+import subprocess
+import random
+import struct
+import math
+try:
+    from . import lab, test_rust_parity as base
+except ImportError:
+    import lab
+    import test_rust_parity as base
+
+
+def corpus():
+    def bits(v):return struct.pack('>d',float(v)).hex()
+    def row(fall=2,dy=-.08,ground=True,water=False,support=None,after_support=None,mutate=False,fail=-1):return dict(fall=bits(fall),dy=bits(dy),ground=ground,water=water,support=support,after_support=after_support,mutate=mutate,fail=fail)
+    values=[-float('inf'),-1e40,-1,-.08,-1e-46,-0.0,0,1e-46,.08,1,1e40,float('inf'),float('nan')]
+    for fall in values:
+        for dy in values:
+            for ground in [False,True]:
+                for water in [False,True]:
+                    for support in [None,[17,-64,-33]]:yield row(fall,dy,ground,water,support)
+    for fall in [-1,0,2,float('nan')]:
+        for dy in [-1,-1e-46,0,1]:
+            for support in [None,[17,-64,-33]]:
+                for after in [None,[31,15,-1]]:
+                    for mutate in [False,True]:
+                        for fail in range(-1,6):yield row(fall,dy,support=support,after_support=after,mutate=mutate,fail=fail)
+    rng=random.Random(0x46414c4c)
+    for _ in range(5000):
+        fall=rng.uniform(-.5,10);dy=rng.uniform(-2,1)
+        if rng.randrange(4)==0:fall=rng.choice(values)
+        if rng.randrange(4)==0:dy=rng.choice(values)
+        yield row(fall,dy,bool(rng.randrange(2)),bool(rng.randrange(2)),rng.choice([None,[17,-64,-33]]),rng.choice([None,[31,15,-1]]),bool(rng.randrange(2)),rng.choice([-1,-1,0,1,2,3,4,5]))
+
+
+def main():
+    parser=argparse.ArgumentParser(description=__doc__);parser.add_argument('--prepare',action='store_true');args=parser.parse_args()
+    build=lab.LOCAL/'rust-fall-damage-parity';build.mkdir(parents=True,exist_ok=True)
+    report_path=build/'report.json';report_path.unlink(missing_ok=True)
+    if args.prepare:lab.prepare()
+    lock,jars,libraries=base.verify_artifacts()
+    oracle=lab.ROOT/'mods/horizon/src/test/java/dev/horizonlab/parity/VanillaFallDamageOracle.java'
+    sources=[oracle,Path(__file__),lab.ROOT/'tools/test_rust_parity.py',lab.ROOT/'tools/lab.py',lab.ROOT/'Cargo.toml',lab.ROOT/'Cargo.lock',lab.ROOT/'crates/horizon-core/Cargo.toml',lab.ROOT/'crates/horizon-world/Cargo.toml',*sorted((lab.ROOT/'crates/horizon-core/src').rglob('*.rs')),*sorted((lab.ROOT/'crates/horizon-world/src').rglob('*.rs')),lab.ROOT/'crates/horizon-world/examples/fall_damage_fixture.rs']
+    tested_sources=base.source_hashes(sources)
+    classes=build/'classes';classes.mkdir(exist_ok=True)
+    def run(command,name):
+        with (build/(name+'.log')).open('w',encoding='utf-8') as log:base.run(list(map(str,command)),stdout=log,stderr=subprocess.STDOUT)
+    dependency_path=os.pathsep.join(map(str,libraries))
+    run(['javac','--release',lock['minecraft']['java_major'],'-proc:none','-cp',str(jars['server'])+os.pathsep+dependency_path,'-d',classes,oracle],'compile-java')
+    def java(side,mode,path):
+        run(['java','-Xmx512M','-cp',os.pathsep.join([str(classes),str(jars[side]),dependency_path]),'dev.horizonlab.parity.VanillaFallDamageOracle',mode,path],side+'-'+mode)
+    fixtures=list(corpus());inputs=build/'inputs.txt';inputs.write_text(''.join(json.dumps(value,separators=(',',':'))+'\n' for value in fixtures),encoding='utf-8')
+    fixture_paths=[inputs];tested_fixtures=base.source_hashes(fixture_paths)
+    run(['cargo','build','--release','-p','horizon-world','--example','fall_damage_fixture'],'compile-rust')
+    metadata=json.loads(subprocess.check_output(['cargo','metadata','--no-deps','--format-version','1'],cwd=lab.ROOT,text=True))
+    binary=Path(metadata['target_directory'])/'release/examples'/('fall_damage_fixture.exe' if os.name=='nt' else 'fall_damage_fixture')
+    run([binary,build],'rust');references=[]
+    for side,jar in jars.items():
+        java(side,side,build);reference=build/f'{side}.txt';matched=base.compare(reference,build/'rust.txt')
+        references.append({'side':side,'jar_sha256':lab.digest(jar,'sha256'),'output_sha256':lab.digest(reference,'sha256'),'matched_output_lines':matched})
+        print(f'{side}: {matched:,} fall-damage output lines match Rust',flush=True)
+    base.ensure_sources_unchanged(sources,tested_sources);base.ensure_sources_unchanged(fixture_paths,tested_fixtures)
+    report={'schema':1,'minecraft':lock['minecraft']['version'],'manifest_sha1':lock['minecraft']['manifest_sha1'],'platform':platform.platform(),'java':subprocess.check_output(['java','--version'],text=True).splitlines()[0],'rustc':subprocess.check_output(['rustc','--version'],text=True).strip(),'fixtures':len(fixtures),'sources_sha256':tested_sources,'fixtures_sha256':tested_fixtures,'rust_output_sha256':lab.digest(build/'rust.txt','sha256'),'references':references,'scope':'Actual base Entity.checkFallDamage with controlled water state, block landing callback, supporting-block lookup, HIT_GROUND emission and reset. Compares float-narrowed downward displacement accumulation, grounded branches, state/position/support mutations during landing, callback order, nonfinite arithmetic and partial state after failures. LivingEntity fluid updates/particles, registered Block.fallOn behavior, health/damage/attributes and the full movement lifecycle are not established by this scoped check.'}
+    lab.write_json(report_path,report);print(f'Scoped fall damage parity passed: {report_path}')
+
+
+if __name__=='__main__':main()