Add stair height smoothing and update navigation controllers

tests/domain/rapier-collision-world.test.ts

@@ -626,6 +626,103 @@ describe("RapierCollisionWorld", () => {
     }
   });
 
+  it("autosteps up authored stairs when the top surface is within the max step height", async () => {
+    const floorBrush = createBoxBrush({
+      id: "brush-floor-stair-climb",
+      center: {
+        x: 0,
+        y: -0.5,
+        z: 0
+      },
+      size: {
+        x: 8,
+        y: 1,
+        z: 10
+      }
+    });
+    const stepOne = createBoxBrush({
+      id: "brush-stair-step-one",
+      center: {
+        x: 0,
+        y: 0.1,
+        z: 0.75
+      },
+      size: {
+        x: 2,
+        y: 0.2,
+        z: 0.5
+      }
+    });
+    const stepTwo = createBoxBrush({
+      id: "brush-stair-step-two",
+      center: {
+        x: 0,
+        y: 0.3,
+        z: 1.25
+      },
+      size: {
+        x: 2,
+        y: 0.6,
+        z: 0.5
+      }
+    });
+    const stepThree = createBoxBrush({
+      id: "brush-stair-step-three",
+      center: {
+        x: 0,
+        y: 0.5,
+        z: 1.75
+      },
+      size: {
+        x: 2,
+        y: 1,
+        z: 0.5
+      }
+    });
+    const runtimeScene = buildRuntimeSceneFromDocument({
+      ...createEmptySceneDocument({ name: "Stair Climb Scene" }),
+      brushes: {
+        [floorBrush.id]: floorBrush,
+        [stepOne.id]: stepOne,
+        [stepTwo.id]: stepTwo,
+        [stepThree.id]: stepThree
+      }
+    });
+    const collisionWorld = await RapierCollisionWorld.create(
+      runtimeScene.colliders,
+      runtimeScene.playerCollider,
+      {
+        maxStepHeight: 0.25
+      }
+    );
+
+    try {
+      let feetPosition = {
+        x: 0,
+        y: 0,
+        z: -0.4
+      };
+
+      for (let index = 0; index < 10; index += 1) {
+        feetPosition = collisionWorld.resolveFirstPersonMotion(
+          feetPosition,
+          {
+            x: 0,
+            y: 0,
+            z: 0.25
+          },
+          runtimeScene.playerCollider
+        ).feetPosition;
+      }
+
+      expect(feetPosition.z).toBeGreaterThan(1.6);
+      expect(feetPosition.y).toBeGreaterThan(0.45);
+      expect(feetPosition.y).toBeLessThan(0.62);
+    } finally {
+      collisionWorld.dispose();
+    }
+  });
+
   it("supports authored Player Start collision mode none without world clipping", async () => {
     const wallBrush = createBoxBrush({
       id: "brush-wall-no-collision",

tests/unit/player-locomotion.test.ts

@@ -11,6 +11,7 @@ import { createIdleRuntimeLocomotionState } from "../../src/runtime-three/player
 import { stepPlayerLocomotion } from "../../src/runtime-three/player-locomotion";
 import type { PlayerStartActionInputState } from "../../src/runtime-three/player-input-bindings";
 import type { RuntimePlayerMovement } from "../../src/runtime-three/runtime-scene-build";
+import { smoothGroundedStairHeight } from "../../src/runtime-three/stair-height-smoothing";
 
 const movementTemplate = createPlayerStartMovementTemplate();
 
@@ -638,6 +639,43 @@ describe("player-locomotion", () => {
     expect(step?.locomotionState.planarSpeed).toBeCloseTo(4.5);
   });
 
+  it("smooths grounded stair height changes instead of snapping", () => {
+    const smoothedHeight = smoothGroundedStairHeight({
+      currentSmoothedFeetY: 0,
+      targetFeetY: 0.2,
+      grounded: true,
+      dt: 1 / 60,
+      maxStepHeight: 0.5
+    });
+
+    expect(smoothedHeight).toBeGreaterThan(0);
+    expect(smoothedHeight).toBeLessThan(0.2);
+  });
+
+  it("snaps grounded height smoothing when the player leaves the ground", () => {
+    const smoothedHeight = smoothGroundedStairHeight({
+      currentSmoothedFeetY: 0,
+      targetFeetY: 0.2,
+      grounded: false,
+      dt: 1 / 60,
+      maxStepHeight: 0.5
+    });
+
+    expect(smoothedHeight).toBeCloseTo(0.2);
+  });
+
+  it("snaps grounded height smoothing for ledge-sized vertical jumps", () => {
+    const smoothedHeight = smoothGroundedStairHeight({
+      currentSmoothedFeetY: 0,
+      targetFeetY: 1,
+      grounded: true,
+      dt: 1 / 60,
+      maxStepHeight: 0.35
+    });
+
+    expect(smoothedHeight).toBeCloseTo(1);
+  });
+
   it("sinks toward the water surface while keeping the head above water", () => {
     const step = stepPlayerLocomotion({
       dt: 0.1,