diff --git a/benchmarks/rust-world-edge-backoff-2026-10-07/scoped-parity.json b/benchmarks/rust-world-edge-backoff-2026-10-07/scoped-parity.json
new file mode 100644
index 0000000000..3dc8ef1a05
--- /dev/null
+++ b/benchmarks/rust-world-edge-backoff-2026-10-07/scoped-parity.json
@@ -0,0 +1,236 @@
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+    "crates/horizon-world/src/worldgen/biome_temperature.rs": "cde4bbab5e260c4065b113376c423b8511ade93c5aa5fd976e245ee8a58b5ad1",
+    "crates/horizon-world/src/worldgen/biome_weather.rs": "96b1f9494559ed31d06257b83d604d00cc069ccc8c7b68094117e034b4a71bd7",
+    "crates/horizon-world/src/worldgen/block_blob.rs": "c608c57b3d77279646ecb89e50677dd8e452b0422ffd357ba755536c5589eb89",
+    "crates/horizon-world/src/worldgen/block_column.rs": "f72c21a9066ee0aa68c2fb79fba436d05afb14c6ef5a2cb012f1ed35fc17cd22",
+    "crates/horizon-world/src/worldgen/block_feature.rs": "36b4e46ee7f7f73bcb94d8bce8d99013e4b16234c9a03542eeb3186e88dd1c21",
+    "crates/horizon-world/src/worldgen/block_pile.rs": "623e369b77e0526ed2756485a6c0bb09683cd28ad8876dea907360ca6665b39d",
+    "crates/horizon-world/src/worldgen/block_predicate.rs": "074c692367e3f2191a1bb28d87b23402430a843c246bd30a4ea838ee3500280e",
+    "crates/horizon-world/src/worldgen/blue_ice.rs": "eedd77bdaff808330b864166d303378096daa5c7d235e925770b171c05109247",
+    "crates/horizon-world/src/worldgen/bonus_chest.rs": "05d0f63fbc7412f13ba1fa37a7238114b8f70bfff318beb2dece590482d49cc0",
+    "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"
+  },
+  "fixtures_sha256": {
+    ".local/rust-world-edge-backoff-parity/inputs.txt": "869a645642747489fb1b26442383c684eed938ea164a326b6d60cc9d5bedfbd5",
+    ".local/rust-world-edge-backoff-parity/facts.json": "5e89a805514cabfe46e082d651db406b9479781e1d97b65faa2ab9f6f871309b",
+    ".local/rust-world-edge-backoff-parity/definitions.json": "9cac3c650353104db1648050621057bfe104dec1f44b53d0b7875f7bc20e6eec",
+    ".local/rust-world-edge-backoff-parity/block-registry.nbt": "5042073c80753f9548cb8fdb5b1000f0e5a1220127a0cc3c6a75737e180bf9bb",
+    ".local/rust-world-edge-backoff-parity/cached-collision.nbt": "4a274cd720a1bda585b02f50f16e90246576679e1e173c214548c5cbf607ab2d",
+    ".local/rust-world-edge-backoff-parity/tags.json": "5e1301e5a9abf7e4de93af5dae3a157e852dbdb4ea345c2eb626305a605d4f98"
+  },
+  "rust_output_sha256": "867e26dc548afc0e892725e62091517032f18e9de6cf9b796a44e37c32464f7c",
+  "references": [
+    {
+      "side": "client",
+      "jar_sha256": "4508d006323f24fa02876310c192d739af56516eb259000ac50f0909a68c9a2d",
+      "output_sha256": "867e26dc548afc0e892725e62091517032f18e9de6cf9b796a44e37c32464f7c",
+      "matched_output_lines": 27109699
+    },
+    {
+      "side": "server",
+      "jar_sha256": "a362163eec5d1612d520772bc16e5b39c09e3b234fdc045f56bf544284ee8ae6",
+      "output_sha256": "867e26dc548afc0e892725e62091517032f18e9de6cf9b796a44e37c32464f7c",
+      "matched_output_lines": 27109699
+    }
+  ],
+  "scope": "Actual Player.maybeBackOffFromEdge issues native noCollision queries over registered block states in resident ProtoChunk storage. Rust combines edge-backoff guards/probe geometry with short-circuit entity-bearing no_world_collision and registry-bound TerrainChunk scanning. Every state is used as the supporting block; additional falling, step-height, chunk-edge, diagonal, partial/dynamic block, mover/flight/crouch and failing-provider cases are compared. Entity collider lists, border applicability/shapes and empty/position/placement contexts remain controlled inputs. This is registered-world ledge integration, not a complete Player.move/travel loop or full playable game."
+}
diff --git a/crates/horizon-world/examples/registry_collision_scan_fixture.rs b/crates/horizon-world/examples/registry_collision_scan_fixture.rs
index 2867bb544f..dff8729087 100644
--- a/crates/horizon-world/examples/registry_collision_scan_fixture.rs
+++ b/crates/horizon-world/examples/registry_collision_scan_fixture.rs
@@ -5,10 +5,11 @@ use horizon_core::{
 };
 use horizon_world::{
     block_collision::{BlockCollisionRegistry, DynamicCollisionWorld, ShulkerCollisionState},
-    block_collision_scan::BlockCollisionScan,
+    block_collision_scan::{BlockCollisionScan, BlockCollisionWorld, CollisionScanError},
     collision::CachedCollisionRegistry,
     collision_context::CollisionContext,
     dynamic_support::DynamicSupportWorld,
+    edge_backoff::{EdgeBackoffInput, EdgeBackoffWorld, back_off_from_edge},
     entity_obstruction::EntityIdentity,
     fluid::FluidState,
     heightmap::HeightmapState,
@@ -242,6 +243,39 @@ impl EntityMovementWorld for World<'_> {
         Ok(border.clone())
     }
 }
+struct EdgeWorld<'w, 'c, W> {
+    world: &'w mut W,
+    context: CollisionContext<'c>,
+    step: f32,
+    grounded: bool,
+    staying: bool,
+}
+impl<W, E> EdgeBackoffWorld for EdgeWorld<'_, '_, W>
+where
+    W: BlockCollisionWorld<Error = E> + EntityMovementWorld<Error = E>,
+{
+    type Error = CollisionScanError<E>;
+    fn max_up_step(&mut self) -> Result<f32, Self::Error> {
+        Ok(self.step)
+    }
+    fn staying_on_ground_surface(&mut self) -> Result<bool, Self::Error> {
+        Ok(self.staying)
+    }
+    fn on_ground(&mut self) -> Result<bool, Self::Error> {
+        Ok(self.grounded)
+    }
+    fn no_collision(&mut self, bounds: Aabb) -> Result<bool, Self::Error> {
+        no_world_collision(
+            self.world,
+            CollisionCheckRequest {
+                entity: EntityIdentity(1),
+                context: self.context,
+                bounds,
+                candidate_budget: 1_000_000,
+            },
+        )
+    }
+}
 impl DynamicSupportWorld for World<'_> {
     type Error = io::Error;
     fn shulker_is_closed(&mut self, p: [i32; 3]) -> io::Result<Option<bool>> {
@@ -449,6 +483,37 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         );
         if let Some(m) = f.get("movement") {
             let v = &m["delta"];
+            if let Some(edge) = m.get("edge") {
+                let mut world = EdgeWorld {
+                    world: &mut bound,
+                    context,
+                    step: number(&m["step"]) as f32,
+                    grounded: m["grounded"].as_bool().unwrap(),
+                    staying: edge["staying"].as_bool().unwrap(),
+                };
+                let result = back_off_from_edge(
+                    &mut world,
+                    EdgeBackoffInput {
+                        movement: Vec3::new(number(&v[0]), number(&v[1]), number(&v[2])),
+                        bounds,
+                        flying: edge["flying"].as_bool().unwrap(),
+                        self_or_player: matches!(
+                            edge["mover"].as_str().unwrap(),
+                            "SELF" | "PLAYER"
+                        ),
+                        fall_distance: number(&edge["fall"]),
+                        query_budget: 10000,
+                    },
+                );
+                let mut t = trace.borrow_mut();
+                match result {
+                    Ok(v) => values(&mut t.out, "edge", [v.x, v.y, v.z])?,
+                    Err(_) => writeln!(t.out, "error")?,
+                };
+                let calls = t.calls;
+                writeln!(t.out, "done edge {calls}")?;
+                continue;
+            }
             if m.get("check").and_then(Value::as_bool) == Some(true) {
                 let result = no_world_collision(
                     &mut bound,
diff --git a/docs/collision-geometry.md b/docs/collision-geometry.md
index 50b9a06a6f..de744df5cd 100644
--- a/docs/collision-geometry.md
+++ b/docs/collision-geometry.md
@@ -639,3 +639,18 @@ guards, fall/step and 0.05 thresholds, nonfinite values and query failures. Two
 query-budget unit tests and workspace Clippy pass. Registered-world ledge probes,
 live crouching/attribute state and the complete player movement loop are separate
 integration work.
+
+
+Registered-world ledge integration now runs `back_off_from_edge` through
+`no_world_collision` and registry-bound resident chunk scans. The native side
+executes actual `Player.maybeBackOffFromEdge` and its collision probes over
+`ProtoChunk` sections. Every state is used as a supporting block, with additional
+falling, step-height, chunk-edge, diagonal, dynamic-block and guard/error cases.
+
+`python3 tools/test_world_edge_backoff_parity.py` passes with
+**27,109,699 matching lines per JAR** in the
+[world ledge report](../benchmarks/rust-world-edge-backoff-2026-10-07/scoped-parity.json).
+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.
diff --git a/mods/horizon/src/test/java/dev/horizonlab/parity/VanillaRegistryCollisionScanOracle.java b/mods/horizon/src/test/java/dev/horizonlab/parity/VanillaRegistryCollisionScanOracle.java
index 7a35b26226..093fc522a1 100644
--- a/mods/horizon/src/test/java/dev/horizonlab/parity/VanillaRegistryCollisionScanOracle.java
+++ b/mods/horizon/src/test/java/dev/horizonlab/parity/VanillaRegistryCollisionScanOracle.java
@@ -49,6 +49,16 @@ public final class VanillaRegistryCollisionScanOracle {
         @Override public boolean onGround(){return grounded;}
         void configure(StepLevel level,AABB bounds,float step,boolean grounded){setLevel(level);setBoundingBox(bounds);this.step=step;this.grounded=grounded;}
     }
+    static final class EdgePlayer extends net.minecraft.world.entity.player.Player {
+        float step;boolean grounded,staying;
+        private EdgePlayer(){super(null,null);}
+        @Override public GameType gameMode(){return GameType.SURVIVAL;}
+        @Override public float maxUpStep(){return step;}
+        @Override public boolean onGround(){return grounded;}
+        @Override protected boolean isStayingOnGroundSurface(){return staying;}
+        void configure(StepLevel level,AABB bounds,float step,boolean grounded,boolean staying){setLevel(level);setBoundingBox(bounds);this.step=step;this.grounded=grounded;this.staying=staying;}
+        Vec3 backoff(Vec3 delta,net.minecraft.world.entity.MoverType mover){return maybeBackOffFromEdge(delta,mover);}
+    }
     static long key(int x,int z){return (long)x<<32|Integer.toUnsignedLong(z);}
     static double number(JsonElement v){return Double.longBitsToDouble(Long.parseUnsignedLong(v.getAsString(),16));}
     public static void main(String[] args)throws Exception {
@@ -65,6 +75,7 @@ public final class VanillaRegistryCollisionScanOracle {
             for(var status:animation.getType().getEnumConstants())if(((Enum<?>)status).name().equals(i==1?"CLOSED":"OPENED"))animation.set(entities[i],status);
             progress.setFloat(entities[i],i==1?0:0.5f);previous.setFloat(entities[i],i==1?0:0.5f);
         }
+        var abilities=net.minecraft.world.entity.player.Player.class.getDeclaredField("abilities");abilities.setAccessible(true);
         var collide=net.minecraft.world.entity.Entity.class.getDeclaredMethod("collide",Vec3.class);collide.setAccessible(true);
         var emit=VanillaFaceSupportOracle.class.getDeclaredMethod("emit",PrintWriter.class,VoxelShape.class);emit.setAccessible(true);
         try(var out=new PrintWriter(Files.newBufferedWriter(dir.resolve(args[0]+".txt")));var lines=Files.lines(dir.resolve("inputs.txt"))){
@@ -85,6 +96,10 @@ public final class VanillaRegistryCollisionScanOracle {
                     level.entities=new ArrayList<>();for(var shape:m.getAsJsonArray("entities"))level.entities.add(boxShape(shape));
                     level.border=new StepBorder();level.border.trace=trace;level.border.shape=m.get("border").isJsonNull()?null:boxShape(m.get("border"));
                     var entity=(StepEntity)allocate.invoke(unsafe,StepEntity.class);entity.configure(level,bounds,(float)number(m.get("step")),m.get("grounded").getAsBoolean());var delta=m.getAsJsonArray("delta");
+                    if(m.has("edge")){
+                        var e=m.getAsJsonObject("edge");var player=(EdgePlayer)allocate.invoke(unsafe,EdgePlayer.class);player.configure(level,bounds,(float)number(m.get("step")),m.get("grounded").getAsBoolean(),e.get("staying").getAsBoolean());player.fallDistance=number(e.get("fall"));var a=new net.minecraft.world.entity.player.Abilities();a.flying=e.get("flying").getAsBoolean();abilities.set(player,a);
+                        try{var result=player.backoff(new Vec3(number(delta.get(0)),number(delta.get(1)),number(delta.get(2))),net.minecraft.world.entity.MoverType.valueOf(e.get("mover").getAsString()));out.printf("edge %016x %016x %016x%n",Double.doubleToLongBits(result.x),Double.doubleToLongBits(result.y),Double.doubleToLongBits(result.z));}catch(Stop error){out.println("error");}out.println("done edge "+trace.calls);continue;
+                    }
                     if(m.has("check")&&m.get("check").getAsBoolean()){try{out.println("clear "+level.noCollision(entity,bounds));}catch(Stop error){out.println("error");}out.println("done check "+trace.calls);continue;}
                     try{var result=(Vec3)collide.invoke(entity,new Vec3(number(delta.get(0)),number(delta.get(1)),number(delta.get(2))));out.printf("movement %016x %016x %016x%n",Double.doubleToLongBits(result.x),Double.doubleToLongBits(result.y),Double.doubleToLongBits(result.z));}
                     catch(InvocationTargetException error){if(error.getCause() instanceof Stop)out.println("error");else throw error;}
diff --git a/tools/test_world_edge_backoff_parity.py b/tools/test_world_edge_backoff_parity.py
new file mode 100644
index 0000000000..eee2b8fb51
--- /dev/null
+++ b/tools/test_world_edge_backoff_parity.py
@@ -0,0 +1,106 @@
+#!/usr/bin/env python3
+"""Compare player ledge backoff through registered world collision probes with pinned vanilla."""
+import collections
+import json
+import os
+from pathlib import Path
+import platform
+import subprocess
+import struct
+import random
+try:
+    from . import lab, test_rust_parity as base, test_worldgen_parity as worldgen
+except ImportError:
+    import lab
+    import test_rust_parity as base
+    import test_worldgen_parity as worldgen
+
+
+def corpus(facts):
+    def bits(v):return struct.pack('>d',float(v)).hex()
+    def row(state,delta=(.8,-.08,.8),step=.6,grounded=True,context=0,offset=0,fail=-1,extra=(),entities=(),border=None,fall=0,staying=True,flying=False,mover='SELF'):
+        blocks=[[offset,-1,0,state],*extra]
+        return dict(chunks=[[x,z] for x in range((offset>>4)-1,(offset>>4)+2) for z in [-1,0,1]],blocks=blocks,context=context,y=bits(0),entities=[0,0],fail=fail,limit=100000,suffocating=False,box=list(map(bits,[offset+.2,0,.2,offset+.8,1.8,.8])),movement=dict(delta=list(map(bits,delta)),step=bits(step),grounded=grounded,entities=[list(map(bits,b)) for b in entities],border=None if border is None else list(map(bits,border)),edge=dict(staying=staying,flying=flying,mover=mover,fall=bits(fall))))
+    states=facts['states'];defaults=facts['defaults']
+    for state in range(len(states)):yield row(state,context=state%4)
+    obstacles=[i for i,s in enumerate(states) if s['id'] in ['minecraft:oak_stairs','minecraft:stone_slab','minecraft:snow','minecraft:scaffolding','minecraft:powder_snow','minecraft:water','minecraft:shulker_box','minecraft:moving_piston','minecraft:piston','minecraft:soul_sand','minecraft:mud','minecraft:farmland','minecraft:bamboo','minecraft:pointed_dripstone']]
+    for state in obstacles:
+        for step in [0,.5,.6,1.0]:
+            for fall in [0,.2,.6,1.0]:yield row(state,step=step,grounded=False,fall=fall,context=state%4)
+    for mover in ['SELF','PLAYER','PISTON','SHULKER','SHULKER_BOX']:
+        for flying in [False,True]:
+            for staying in [False,True]:
+                for y in [-.08,0,.1]:
+                    for fail in [-1,0,1,3,10,30,100]:yield row(defaults['minecraft:stone'],delta=(.8,y,.8),mover=mover,flying=flying,staying=staying,fail=fail)
+    rng=random.Random(0x574f524c44454447)
+    for index in range(2500):
+        offset=rng.choice([-16,0,15]);state=rng.choice(obstacles);delta=[rng.choice([-1,-.05,-0.0,0,.05,.5,.8,1]),rng.choice([-.5,-.08,0,.1]),rng.choice([-1,-.5,0,.5,.8,1])]
+        entities=[] if index%3 else [[offset+.2,-1,.2,offset+.8,0,.8]]
+        border=None if index%4 else [offset+1,-2,-2,offset+1.2,3,3]
+        extra=[] if index%2 else [[offset+1,-1,1,defaults['minecraft:stone']]]
+        f=row(state,delta,step=rng.choice([0,.5,.6,1]),grounded=bool(index%2),context=index%4,offset=offset,fail=rng.choice([-1,-1,0,3,15,50]),entities=entities,border=border,extra=extra,fall=rng.choice([0,.2,.6,1]));f['entities']=[rng.randrange(3),rng.randrange(3)];yield f
+
+
+def main():
+    lock, jars, libraries = base.verify_artifacts()
+    build = lab.LOCAL/'rust-world-edge-backoff-parity';build.mkdir(exist_ok=True)
+    report_path = build/'report.json';report_path.unlink(missing_ok=True)
+    oracle = lab.ROOT/'mods/horizon/src/test/java/dev/horizonlab/parity/VanillaRegistryCollisionScanOracle.java'
+    helpers = [oracle.with_name(name+'.java') for name in
+               ['VanillaHeightmapOracle', 'VanillaCollisionOracle', 'VanillaBlockStateCodecOracle', 'VanillaSuffocationOracle', 'VanillaFaceSupportOracle']]
+    sources = [oracle, *helpers, Path(__file__), lab.ROOT/'tools/test_rust_parity.py',
+               lab.ROOT/'tools/test_worldgen_parity.py', lab.ROOT/'tools/lab.py',
+               lab.ROOT/'Cargo.toml', lab.ROOT/'Cargo.lock',
+               lab.ROOT/'crates/horizon-world/examples/registry_collision_scan_fixture.rs']
+    for crate in ['horizon-core', 'horizon-world']:
+        sources += [lab.ROOT/'crates'/crate/'Cargo.toml',
+                    *sorted((lab.ROOT/'crates'/crate/'src').rglob('*.rs'))]
+    tested = base.source_hashes(sources)
+    tags = worldgen.tag_resources(jars['server'])
+    if tags != worldgen.tag_resources(jars['client']):raise AssertionError('Client/server block tags differ')
+    lab.write_json(build/'tags.json', tags)
+    classes = build/'classes';classes.mkdir(exist_ok=True)
+    dependencies = os.pathsep.join(map(str, libraries))
+    def run(command, name):
+        with (build/(name+'.log')).open('w') as log:
+            subprocess.run(list(map(str, command)), cwd=lab.ROOT, check=True, timeout=3600,
+                           stdout=log, stderr=subprocess.STDOUT)
+    run(['javac', '--release', lock['minecraft']['java_major'], '-proc:none', '-cp',
+         str(jars['server'])+os.pathsep+dependencies, '-d', classes, oracle, *helpers], 'compile-java')
+    def java(side, mode):
+        run(['java', '-Xmx768M', '-cp', os.pathsep.join([str(classes), str(jars[side]), dependencies]),
+             'dev.horizonlab.parity.VanillaRegistryCollisionScanOracle', mode, build], side+'-'+mode)
+    java('server', 'export')
+    facts = json.loads((build/'facts.json').read_text())
+    if len(facts['states']) != 35723:raise AssertionError('Incomplete pinned registry')
+    definitions = json.loads((build/'definitions.json').read_text())
+    count = 0
+    with (build/'inputs.txt').open('w') as output:
+        for fixture in corpus(facts):
+            output.write(json.dumps(fixture, separators=(',', ':'))+'\n');count += 1
+    fixture_paths = [build/name for name in ['inputs.txt', 'facts.json', 'definitions.json',
+                                            'block-registry.nbt', 'cached-collision.nbt', 'tags.json']]
+    fixtures = base.source_hashes(fixture_paths)
+    run(['cargo', 'build', '--locked', '--release', '-p', 'horizon-world', '--example', 'registry_collision_scan_fixture'], 'compile-rust')
+    metadata = json.loads(subprocess.check_output(['cargo', 'metadata', '--locked', '--no-deps', '--format-version', '1'], cwd=lab.ROOT))
+    binary = Path(metadata['target_directory'])/'release/examples'/('registry_collision_scan_fixture.exe' if os.name=='nt' else 'registry_collision_scan_fixture')
+    run([binary, build], 'rust');references = []
+    for side, jar in jars.items():
+        java(side, side)
+        matched = base.compare(build/(side+'.txt'), build/'rust.txt')
+        references.append({'side':side, 'jar_sha256':lab.digest(jar, 'sha256'),
+                           'output_sha256':lab.digest(build/(side+'.txt'), 'sha256'), 'matched_output_lines':matched})
+        print(f'{side}: {matched:,} world edge-backoff lines match', flush=True)
+    base.ensure_sources_unchanged(sources, tested);base.ensure_sources_unchanged(fixture_paths, 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(),
+              'registry_states':len(facts['states']), 'block_definitions':len(definitions),
+              'definition_counts':dict(collections.Counter(definitions.values())),
+              'native_chunk_storage':'ProtoChunk', 'rust_chunk_storage':'TerrainChunk', 'fixtures':count, 'sources_sha256':tested, 'fixtures_sha256':fixtures,
+              'rust_output_sha256':lab.digest(build/'rust.txt', 'sha256'), 'references':references,
+              'scope':'Actual Player.maybeBackOffFromEdge issues native noCollision queries over registered block states in resident ProtoChunk storage. Rust combines edge-backoff guards/probe geometry with short-circuit entity-bearing no_world_collision and registry-bound TerrainChunk scanning. Every state is used as the supporting block; additional falling, step-height, chunk-edge, diagonal, partial/dynamic block, mover/flight/crouch and failing-provider cases are compared. Entity collider lists, border applicability/shapes and empty/position/placement contexts remain controlled inputs. This is registered-world ledge integration, not a complete Player.move/travel loop or full playable game.'}
+    lab.write_json(report_path, report);print(f'Scoped world edge backoff parity passed: {report_path}', flush=True)
+
+
+if __name__ == '__main__':main()