diff --git a/src/materials/starter-material-textures.ts b/src/materials/starter-material-textures.ts
new file mode 100644
index 00000000..2c08a3c5
--- /dev/null
+++ b/src/materials/starter-material-textures.ts
@@ -0,0 +1,89 @@
+import { CanvasTexture, RepeatWrapping, SRGBColorSpace } from "three";
+
+import type { MaterialDef } from "./starter-material-library";
+
+export function createStarterMaterialSignature(material: MaterialDef): string {
+  return `${material.baseColorHex}|${material.accentColorHex}|${material.pattern}`;
+}
+
+function fillMaterialPattern(context: CanvasRenderingContext2D, material: MaterialDef, size: number) {
+  context.fillStyle = material.baseColorHex;
+  context.fillRect(0, 0, size, size);
+  context.strokeStyle = material.accentColorHex;
+  context.fillStyle = material.accentColorHex;
+
+  switch (material.pattern) {
+    case "grid":
+      context.lineWidth = Math.max(2, size / 32);
+
+      for (let offset = 0; offset <= size; offset += size / 4) {
+        context.beginPath();
+        context.moveTo(offset, 0);
+        context.lineTo(offset, size);
+        context.stroke();
+
+        context.beginPath();
+        context.moveTo(0, offset);
+        context.lineTo(size, offset);
+        context.stroke();
+      }
+      break;
+    case "checker": {
+      const checkerSize = size / 4;
+
+      for (let row = 0; row < 4; row += 1) {
+        for (let column = 0; column < 4; column += 1) {
+          if ((row + column) % 2 === 0) {
+            context.fillRect(column * checkerSize, row * checkerSize, checkerSize, checkerSize);
+          }
+        }
+      }
+      break;
+    }
+    case "stripes":
+      context.lineWidth = size / 6;
+
+      for (let offset = -size; offset <= size * 2; offset += size / 3) {
+        context.beginPath();
+        context.moveTo(offset, size);
+        context.lineTo(offset + size, 0);
+        context.stroke();
+      }
+      break;
+    case "diamond":
+      context.lineWidth = Math.max(2, size / 28);
+
+      for (let offset = -size; offset <= size; offset += size / 3) {
+        context.beginPath();
+        context.moveTo(size * 0.5, offset);
+        context.lineTo(size - offset, size * 0.5);
+        context.lineTo(size * 0.5, size - offset);
+        context.lineTo(-offset, size * 0.5);
+        context.closePath();
+        context.stroke();
+      }
+      break;
+  }
+}
+
+export function createStarterMaterialTexture(material: MaterialDef, size = 128): CanvasTexture {
+  const canvas = document.createElement("canvas");
+  canvas.width = size;
+  canvas.height = size;
+
+  const context = canvas.getContext("2d");
+
+  if (context === null) {
+    throw new Error("2D canvas context is unavailable for starter material texture generation.");
+  }
+
+  fillMaterialPattern(context, material, size);
+
+  const texture = new CanvasTexture(canvas);
+  texture.wrapS = RepeatWrapping;
+  texture.wrapT = RepeatWrapping;
+  texture.colorSpace = SRGBColorSpace;
+  texture.needsUpdate = true;
+
+  return texture;
+}
diff --git a/src/runner-web/RunnerCanvas.tsx b/src/runner-web/RunnerCanvas.tsx
new file mode 100644
index 00000000..e42a6d69
--- /dev/null
+++ b/src/runner-web/RunnerCanvas.tsx
@@ -0,0 +1,79 @@
+import { useEffect, useRef, useState } from "react";
+
+import type { FirstPersonTelemetry } from "../runtime-three/navigation-controller";
+import { RuntimeHost } from "../runtime-three/runtime-host";
+import type { RuntimeNavigationMode, RuntimeSceneDefinition } from "../runtime-three/runtime-scene-build";
+
+interface RunnerCanvasProps {
+  runtimeScene: RuntimeSceneDefinition;
+  navigationMode: RuntimeNavigationMode;
+  onRuntimeMessageChange(message: string | null): void;
+  onFirstPersonTelemetryChange(telemetry: FirstPersonTelemetry | null): void;
+}
+
+export function RunnerCanvas({
+  runtimeScene,
+  navigationMode,
+  onRuntimeMessageChange,
+  onFirstPersonTelemetryChange
+}: RunnerCanvasProps) {
+  const containerRef = useRef<HTMLDivElement | null>(null);
+  const hostRef = useRef<RuntimeHost | null>(null);
+  const [runnerMessage, setRunnerMessage] = useState<string | null>(null);
+
+  useEffect(() => {
+    const container = containerRef.current;
+
+    if (container === null) {
+      return;
+    }
+
+    const testCanvas = document.createElement("canvas");
+    const hasWebGl =
+      testCanvas.getContext("webgl2") !== null ||
+      testCanvas.getContext("webgl") !== null ||
+      testCanvas.getContext("experimental-webgl") !== null;
+
+    if (!hasWebGl) {
+      setRunnerMessage("WebGL is unavailable in this browser environment. The runner shell is visible, but runtime rendering is disabled.");
+      return;
+    }
+
+    try {
+      const runtimeHost = new RuntimeHost();
+      hostRef.current = runtimeHost;
+      runtimeHost.mount(container);
+      runtimeHost.setRuntimeMessageHandler(onRuntimeMessageChange);
+      runtimeHost.setFirstPersonTelemetryHandler(onFirstPersonTelemetryChange);
+      setRunnerMessage(null);
+
+      return () => {
+        runtimeHost.dispose();
+        hostRef.current = null;
+      };
+    } catch (error) {
+      const message = error instanceof Error ? error.message : "Runner initialization failed.";
+      setRunnerMessage(`Runner initialization failed: ${message}`);
+      return;
+    }
+  }, [onFirstPersonTelemetryChange, onRuntimeMessageChange]);
+
+  useEffect(() => {
+    hostRef.current?.loadScene(runtimeScene);
+  }, [runtimeScene]);
+
+  useEffect(() => {
+    hostRef.current?.setNavigationMode(navigationMode);
+  }, [navigationMode]);
+
+  return (
+    <div ref={containerRef} className="runner-canvas" data-testid="runner-shell" aria-label="Built-in scene runner">
+      {runnerMessage === null ? null : (
+        <div className="runner-canvas__fallback" role="status">
+          <div className="runner-canvas__fallback-title">Runner Unavailable</div>
+          <div>{runnerMessage}</div>
+        </div>
+      )}
+    </div>
+  );
+}
diff --git a/src/runtime-three/first-person-navigation-controller.ts b/src/runtime-three/first-person-navigation-controller.ts
new file mode 100644
index 00000000..c36910a5
--- /dev/null
+++ b/src/runtime-three/first-person-navigation-controller.ts
@@ -0,0 +1,232 @@
+import { Euler, Vector3 } from "three";
+
+import type { Vec3 } from "../core/vector";
+
+import { FIRST_PERSON_PLAYER_SHAPE, resolveFirstPersonMotion } from "./player-collision";
+import type { NavigationController, RuntimeControllerContext } from "./navigation-controller";
+
+const LOOK_SENSITIVITY = 0.0022;
+const MOVE_SPEED = 4.5;
+const GRAVITY = 22;
+const MAX_PITCH_RADIANS = Math.PI * 0.48;
+
+function clampPitch(pitchRadians: number): number {
+  return Math.max(-MAX_PITCH_RADIANS, Math.min(MAX_PITCH_RADIANS, pitchRadians));
+}
+
+function toEyePosition(feetPosition: Vec3): Vec3 {
+  return {
+    x: feetPosition.x,
+    y: feetPosition.y + FIRST_PERSON_PLAYER_SHAPE.eyeHeight,
+    z: feetPosition.z
+  };
+}
+
+export class FirstPersonNavigationController implements NavigationController {
+  readonly id = "firstPerson" as const;
+
+  private context: RuntimeControllerContext | null = null;
+  private readonly pressedKeys = new Set<string>();
+  private readonly cameraRotation = new Euler(0, 0, 0, "YXZ");
+  private readonly forwardVector = new Vector3();
+  private readonly rightVector = new Vector3();
+  private feetPosition = {
+    x: 0,
+    y: 0,
+    z: 0
+  };
+  private yawRadians = 0;
+  private pitchRadians = 0;
+  private verticalVelocity = 0;
+  private grounded = false;
+  private pointerLocked = false;
+  private initializedFromSpawn = false;
+
+  activate(ctx: RuntimeControllerContext): void {
+    this.context = ctx;
+
+    if (!this.initializedFromSpawn) {
+      const spawn = ctx.getRuntimeScene().spawn;
+      this.feetPosition = {
+        ...spawn.position
+      };
+      this.yawRadians = (spawn.yawDegrees * Math.PI) / 180;
+      this.pitchRadians = 0;
+      this.verticalVelocity = 0;
+      this.grounded = false;
+      this.initializedFromSpawn = true;
+    }
+
+    window.addEventListener("keydown", this.handleKeyDown);
+    window.addEventListener("keyup", this.handleKeyUp);
+    window.addEventListener("blur", this.handleBlur);
+    document.addEventListener("mousemove", this.handleMouseMove);
+    document.addEventListener("pointerlockchange", this.handlePointerLockChange);
+    document.addEventListener("pointerlockerror", this.handlePointerLockError);
+    ctx.domElement.addEventListener("pointerdown", this.handlePointerDown);
+
+    this.syncPointerLockState();
+    this.updateCameraTransform();
+    this.publishTelemetry();
+  }
+
+  deactivate(ctx: RuntimeControllerContext): void {
+    window.removeEventListener("keydown", this.handleKeyDown);
+    window.removeEventListener("keyup", this.handleKeyUp);
+    window.removeEventListener("blur", this.handleBlur);
+    document.removeEventListener("mousemove", this.handleMouseMove);
+    document.removeEventListener("pointerlockchange", this.handlePointerLockChange);
+    document.removeEventListener("pointerlockerror", this.handlePointerLockError);
+    ctx.domElement.removeEventListener("pointerdown", this.handlePointerDown);
+    this.pressedKeys.clear();
+
+    if (document.pointerLockElement === ctx.domElement) {
+      document.exitPointerLock();
+    }
+
+    this.pointerLocked = false;
+    ctx.setRuntimeMessage(null);
+    ctx.setFirstPersonTelemetry(null);
+    this.context = null;
+  }
+
+  update(dt: number): void {
+    if (this.context === null) {
+      return;
+    }
+
+    const inputX = (this.pressedKeys.has("KeyD") ? 1 : 0) - (this.pressedKeys.has("KeyA") ? 1 : 0);
+    const inputZ = (this.pressedKeys.has("KeyW") ? 1 : 0) - (this.pressedKeys.has("KeyS") ? 1 : 0);
+    const inputLength = Math.hypot(inputX, inputZ);
+
+    let horizontalX = 0;
+    let horizontalZ = 0;
+
+    if (inputLength > 0) {
+      const normalizedInputX = inputX / inputLength;
+      const normalizedInputZ = inputZ / inputLength;
+      const moveDistance = MOVE_SPEED * dt;
+
+      this.forwardVector.set(Math.sin(this.yawRadians), 0, Math.cos(this.yawRadians));
+      this.rightVector.set(Math.cos(this.yawRadians), 0, -Math.sin(this.yawRadians));
+
+      horizontalX = (this.forwardVector.x * normalizedInputZ + this.rightVector.x * normalizedInputX) * moveDistance;
+      horizontalZ = (this.forwardVector.z * normalizedInputZ + this.rightVector.z * normalizedInputX) * moveDistance;
+    }
+
+    this.verticalVelocity -= GRAVITY * dt;
+
+    const resolvedMotion = resolveFirstPersonMotion(
+      this.feetPosition,
+      {
+        x: horizontalX,
+        y: this.verticalVelocity * dt,
+        z: horizontalZ
+      },
+      FIRST_PERSON_PLAYER_SHAPE,
+      this.context.getRuntimeScene().colliders
+    );
+
+    this.feetPosition = resolvedMotion.feetPosition;
+    this.grounded = resolvedMotion.grounded;
+
+    if (this.grounded && this.verticalVelocity < 0) {
+      this.verticalVelocity = 0;
+    }
+
+    this.updateCameraTransform();
+    this.publishTelemetry();
+  }
+
+  private updateCameraTransform() {
+    if (this.context === null) {
+      return;
+    }
+
+    const eyePosition = toEyePosition(this.feetPosition);
+    this.cameraRotation.x = this.pitchRadians;
+    this.cameraRotation.y = this.yawRadians;
+    this.cameraRotation.z = 0;
+
+    this.context.camera.position.set(eyePosition.x, eyePosition.y, eyePosition.z);
+    this.context.camera.rotation.copy(this.cameraRotation);
+  }
+
+  private publishTelemetry() {
+    if (this.context === null) {
+      return;
+    }
+
+    this.context.setFirstPersonTelemetry({
+      feetPosition: {
+        ...this.feetPosition
+      },
+      eyePosition: toEyePosition(this.feetPosition),
+      grounded: this.grounded,
+      pointerLocked: this.pointerLocked,
+      spawn: this.context.getRuntimeScene().spawn
+    });
+  }
+
+  private syncPointerLockState() {
+    if (this.context === null) {
+      return;
+    }
+
+    const pointerLocked = document.pointerLockElement === this.context.domElement;
+    this.pointerLocked = pointerLocked;
+    this.context.setRuntimeMessage(
+      pointerLocked
+        ? "Mouse look active. Press Escape to release the cursor or switch to Orbit Visitor."
+        : "Click inside the runner viewport to capture mouse look. If pointer lock fails, switch to Orbit Visitor."
+    );
+    this.publishTelemetry();
+  }
+
+  private handleKeyDown = (event: KeyboardEvent) => {
+    this.pressedKeys.add(event.code);
+  };
+
+  private handleKeyUp = (event: KeyboardEvent) => {
+    this.pressedKeys.delete(event.code);
+  };
+
+  private handleBlur = () => {
+    this.pressedKeys.clear();
+  };
+
+  private handleMouseMove = (event: MouseEvent) => {
+    if (!this.pointerLocked) {
+      return;
+    }
+
+    this.yawRadians -= event.movementX * LOOK_SENSITIVITY;
+    this.pitchRadians = clampPitch(this.pitchRadians - event.movementY * LOOK_SENSITIVITY);
+  };
+
+  private handlePointerLockChange = () => {
+    this.syncPointerLockState();
+  };
+
+  private handlePointerLockError = () => {
+    this.context?.setRuntimeMessage(
+      "Pointer lock was unavailable in this browser context. Orbit Visitor remains available as the non-FPS fallback."
+    );
+  };
+
+  private handlePointerDown = () => {
+    if (this.context === null || document.pointerLockElement === this.context.domElement) {
+      return;
+    }
+
+    const pointerLockResult = this.context.domElement.requestPointerLock();
+
+    if (pointerLockResult !== undefined && "catch" in pointerLockResult) {
+      pointerLockResult.catch(() => {
+        this.context?.setRuntimeMessage(
+          "Pointer lock request was denied. Click again or use Orbit Visitor for non-locked navigation."
+        );
+      });
+    }
+  };
+}
diff --git a/src/runtime-three/navigation-controller.ts b/src/runtime-three/navigation-controller.ts
new file mode 100644
index 00000000..0524586b
--- /dev/null
+++ b/src/runtime-three/navigation-controller.ts
@@ -0,0 +1,28 @@
+import type { PerspectiveCamera } from "three";
+
+import type { Vec3 } from "../core/vector";
+
+import type { RuntimeNavigationMode, RuntimeSceneDefinition, RuntimeSpawnPoint } from "./runtime-scene-build";
+
+export interface FirstPersonTelemetry {
+  feetPosition: Vec3;
+  eyePosition: Vec3;
+  grounded: boolean;
+  pointerLocked: boolean;
+  spawn: RuntimeSpawnPoint;
+}
+
+export interface RuntimeControllerContext {
+  camera: PerspectiveCamera;
+  domElement: HTMLCanvasElement;
+  getRuntimeScene(): RuntimeSceneDefinition;
+  setRuntimeMessage(message: string | null): void;
+  setFirstPersonTelemetry(telemetry: FirstPersonTelemetry | null): void;
+}
+
+export interface NavigationController {
+  id: RuntimeNavigationMode;
+  activate(ctx: RuntimeControllerContext): void;
+  deactivate(ctx: RuntimeControllerContext): void;
+  update(dt: number): void;
+}
diff --git a/src/runtime-three/orbit-visitor-navigation-controller.ts b/src/runtime-three/orbit-visitor-navigation-controller.ts
new file mode 100644
index 00000000..0e34f24c
--- /dev/null
+++ b/src/runtime-three/orbit-visitor-navigation-controller.ts
@@ -0,0 +1,145 @@
+import { Vector3 } from "three";
+
+import type { Vec3 } from "../core/vector";
+
+import type { NavigationController, RuntimeControllerContext } from "./navigation-controller";
+
+const MIN_DISTANCE = 2;
+const MAX_DISTANCE = 48;
+const MIN_PITCH = 0.15;
+const MAX_PITCH = Math.PI * 0.48;
+
+function clampDistance(distance: number): number {
+  return Math.max(MIN_DISTANCE, Math.min(MAX_DISTANCE, distance));
+}
+
+function clampPitch(pitchRadians: number): number {
+  return Math.max(MIN_PITCH, Math.min(MAX_PITCH, pitchRadians));
+}
+
+function cloneVec3(vector: Vec3): Vec3 {
+  return {
+    x: vector.x,
+    y: vector.y,
+    z: vector.z
+  };
+}
+
+export class OrbitVisitorNavigationController implements NavigationController {
+  readonly id = "orbitVisitor" as const;
+
+  private context: RuntimeControllerContext | null = null;
+  private readonly lookAtVector = new Vector3();
+  private target: Vec3 = {
+    x: 0,
+    y: 0,
+    z: 0
+  };
+  private distance = 8;
+  private yawRadians = Math.PI * 0.25;
+  private pitchRadians = Math.PI * 0.35;
+  private dragging = false;
+  private lastPointerClientX = 0;
+  private lastPointerClientY = 0;
+  private initializedFromScene = false;
+
+  activate(ctx: RuntimeControllerContext): void {
+    this.context = ctx;
+
+    if (!this.initializedFromScene) {
+      const runtimeScene = ctx.getRuntimeScene();
+      const focusPoint = runtimeScene.playerStart?.position ?? runtimeScene.sceneBounds?.center ?? this.target;
+      const focusDistance = runtimeScene.sceneBounds
+        ? Math.max(runtimeScene.sceneBounds.size.x, runtimeScene.sceneBounds.size.y, runtimeScene.sceneBounds.size.z) * 1.1
+        : 8;
+
+      this.target = cloneVec3(focusPoint);
+      this.distance = clampDistance(focusDistance);
+      this.initializedFromScene = true;
+    }
+
+    ctx.domElement.addEventListener("pointerdown", this.handlePointerDown);
+    ctx.domElement.addEventListener("wheel", this.handleWheel, { passive: false });
+    ctx.domElement.addEventListener("contextmenu", this.handleContextMenu);
+    window.addEventListener("pointermove", this.handlePointerMove);
+    window.addEventListener("pointerup", this.handlePointerUp);
+
+    ctx.setRuntimeMessage("Orbit Visitor active. Drag to orbit around the scene and use the mouse wheel to zoom.");
+    ctx.setFirstPersonTelemetry(null);
+    this.updateCameraTransform();
+  }
+
+  deactivate(ctx: RuntimeControllerContext): void {
+    ctx.domElement.removeEventListener("pointerdown", this.handlePointerDown);
+    ctx.domElement.removeEventListener("wheel", this.handleWheel);
+    ctx.domElement.removeEventListener("contextmenu", this.handleContextMenu);
+    window.removeEventListener("pointermove", this.handlePointerMove);
+    window.removeEventListener("pointerup", this.handlePointerUp);
+    ctx.setRuntimeMessage(null);
+    this.dragging = false;
+    this.context = null;
+  }
+
+  update(): void {
+    this.updateCameraTransform();
+  }
+
+  setFocusPoint(target: Vec3): void {
+    this.target = cloneVec3(target);
+    this.updateCameraTransform();
+  }
+
+  private updateCameraTransform() {
+    if (this.context === null) {
+      return;
+    }
+
+    const horizontalDistance = Math.cos(this.pitchRadians) * this.distance;
+    const cameraPosition = {
+      x: this.target.x + Math.sin(this.yawRadians) * horizontalDistance,
+      y: this.target.y + Math.sin(this.pitchRadians) * this.distance,
+      z: this.target.z + Math.cos(this.yawRadians) * horizontalDistance
+    };
+
+    this.context.camera.position.set(cameraPosition.x, cameraPosition.y, cameraPosition.z);
+    this.lookAtVector.set(this.target.x, this.target.y, this.target.z);
+    this.context.camera.lookAt(this.lookAtVector);
+  }
+
+  private handlePointerDown = (event: PointerEvent) => {
+    if (event.button !== 0) {
+      return;
+    }
+
+    this.dragging = true;
+    this.lastPointerClientX = event.clientX;
+    this.lastPointerClientY = event.clientY;
+  };
+
+  private handlePointerMove = (event: PointerEvent) => {
+    if (!this.dragging) {
+      return;
+    }
+
+    const deltaX = event.clientX - this.lastPointerClientX;
+    const deltaY = event.clientY - this.lastPointerClientY;
+    this.lastPointerClientX = event.clientX;
+    this.lastPointerClientY = event.clientY;
+
+    this.yawRadians -= deltaX * 0.008;
+    this.pitchRadians = clampPitch(this.pitchRadians + deltaY * 0.008);
+  };
+
+  private handlePointerUp = () => {
+    this.dragging = false;
+  };
+
+  private handleWheel = (event: WheelEvent) => {
+    event.preventDefault();
+    this.distance = clampDistance(this.distance + event.deltaY * 0.01);
+  };
+
+  private handleContextMenu = (event: MouseEvent) => {
+    event.preventDefault();
+  };
+}
diff --git a/src/runtime-three/player-collision.ts b/src/runtime-three/player-collision.ts
new file mode 100644
index 00000000..d1f3604c
--- /dev/null
+++ b/src/runtime-three/player-collision.ts
@@ -0,0 +1,149 @@
+import type { Vec3 } from "../core/vector";
+
+import type { RuntimeBoxCollider } from "./runtime-scene-build";
+
+export interface FirstPersonPlayerShape {
+  radius: number;
+  height: number;
+  eyeHeight: number;
+}
+
+export interface ResolvedPlayerMotion {
+  feetPosition: Vec3;
+  grounded: boolean;
+  collidedAxes: {
+    x: boolean;
+    y: boolean;
+    z: boolean;
+  };
+}
+
+export const FIRST_PERSON_PLAYER_SHAPE: FirstPersonPlayerShape = {
+  radius: 0.3,
+  height: 1.8,
+  eyeHeight: 1.6
+};
+
+type Axis = "x" | "y" | "z";
+
+interface RuntimeAabb {
+  min: Vec3;
+  max: Vec3;
+}
+
+function createPlayerAabb(feetPosition: Vec3, shape: FirstPersonPlayerShape): RuntimeAabb {
+  return {
+    min: {
+      x: feetPosition.x - shape.radius,
+      y: feetPosition.y,
+      z: feetPosition.z - shape.radius
+    },
+    max: {
+      x: feetPosition.x + shape.radius,
+      y: feetPosition.y + shape.height,
+      z: feetPosition.z + shape.radius
+    }
+  };
+}
+
+function rangesOverlap(minA: number, maxA: number, minB: number, maxB: number): boolean {
+  return minA < maxB && maxA > minB;
+}
+
+function resolveAxis(
+  axis: Axis,
+  nextFeetPosition: Vec3,
+  delta: number,
+  shape: FirstPersonPlayerShape,
+  colliders: RuntimeBoxCollider[]
+): { collided: boolean; grounded: boolean } {
+  if (delta === 0) {
+    return {
+      collided: false,
+      grounded: false
+    };
+  }
+
+  nextFeetPosition[axis] += delta;
+
+  let collided = false;
+  let grounded = false;
+
+  for (const collider of colliders) {
+    const playerAabb = createPlayerAabb(nextFeetPosition, shape);
+    const overlapsOtherAxes =
+      axis === "x"
+        ? rangesOverlap(playerAabb.min.y, playerAabb.max.y, collider.min.y, collider.max.y) &&
+          rangesOverlap(playerAabb.min.z, playerAabb.max.z, collider.min.z, collider.max.z)
+        : axis === "y"
+          ? rangesOverlap(playerAabb.min.x, playerAabb.max.x, collider.min.x, collider.max.x) &&
+            rangesOverlap(playerAabb.min.z, playerAabb.max.z, collider.min.z, collider.max.z)
+          : rangesOverlap(playerAabb.min.x, playerAabb.max.x, collider.min.x, collider.max.x) &&
+            rangesOverlap(playerAabb.min.y, playerAabb.max.y, collider.min.y, collider.max.y);
+
+    if (!overlapsOtherAxes) {
+      continue;
+    }
+
+    switch (axis) {
+      case "x":
+        if (delta > 0 && playerAabb.max.x > collider.min.x && playerAabb.min.x < collider.min.x) {
+          nextFeetPosition.x = collider.min.x - shape.radius;
+          collided = true;
+        } else if (delta < 0 && playerAabb.min.x < collider.max.x && playerAabb.max.x > collider.max.x) {
+          nextFeetPosition.x = collider.max.x + shape.radius;
+          collided = true;
+        }
+        break;
+      case "y":
+        if (delta > 0 && playerAabb.max.y > collider.min.y && playerAabb.min.y < collider.min.y) {
+          nextFeetPosition.y = collider.min.y - shape.height;
+          collided = true;
+        } else if (delta < 0 && playerAabb.min.y < collider.max.y && playerAabb.max.y > collider.max.y) {
+          nextFeetPosition.y = collider.max.y;
+          collided = true;
+          grounded = true;
+        }
+        break;
+      case "z":
+        if (delta > 0 && playerAabb.max.z > collider.min.z && playerAabb.min.z < collider.min.z) {
+          nextFeetPosition.z = collider.min.z - shape.radius;
+          collided = true;
+        } else if (delta < 0 && playerAabb.min.z < collider.max.z && playerAabb.max.z > collider.max.z) {
+          nextFeetPosition.z = collider.max.z + shape.radius;
+          collided = true;
+        }
+        break;
+    }
+  }
+
+  return {
+    collided,
+    grounded
+  };
+}
+
+export function resolveFirstPersonMotion(
+  feetPosition: Vec3,
+  motion: Vec3,
+  shape: FirstPersonPlayerShape,
+  colliders: RuntimeBoxCollider[]
+): ResolvedPlayerMotion {
+  const nextFeetPosition = {
+    ...feetPosition
+  };
+
+  const xResolution = resolveAxis("x", nextFeetPosition, motion.x, shape, colliders);
+  const zResolution = resolveAxis("z", nextFeetPosition, motion.z, shape, colliders);
+  const yResolution = resolveAxis("y", nextFeetPosition, motion.y, shape, colliders);
+
+  return {
+    feetPosition: nextFeetPosition,
+    grounded: yResolution.grounded,
+    collidedAxes: {
+      x: xResolution.collided,
+      y: yResolution.collided,
+      z: zResolution.collided
+    }
+  };
+}
diff --git a/src/runtime-three/runtime-host.ts b/src/runtime-three/runtime-host.ts
new file mode 100644
index 00000000..ea0f69d7
--- /dev/null
+++ b/src/runtime-three/runtime-host.ts
@@ -0,0 +1,272 @@
+import {
+  AmbientLight,
+  BoxGeometry,
+  Color,
+  DirectionalLight,
+  Group,
+  Mesh,
+  MeshStandardMaterial,
+  PerspectiveCamera,
+  Scene,
+  WebGLRenderer
+} from "three";
+
+import { applyBoxBrushFaceUvsToGeometry } from "../geometry/box-face-uvs";
+import { createStarterMaterialSignature, createStarterMaterialTexture } from "../materials/starter-material-textures";
+
+import { FirstPersonNavigationController } from "./first-person-navigation-controller";
+import type { FirstPersonTelemetry, NavigationController, RuntimeControllerContext } from "./navigation-controller";
+import { OrbitVisitorNavigationController } from "./orbit-visitor-navigation-controller";
+import type { RuntimeBoxBrushInstance, RuntimeNavigationMode, RuntimeSceneDefinition } from "./runtime-scene-build";
+
+interface CachedMaterialTexture {
+  signature: string;
+  texture: ReturnType<typeof createStarterMaterialTexture>;
+}
+
+const FALLBACK_FACE_COLOR = 0x747d89;
+
+export class RuntimeHost {
+  private readonly scene = new Scene();
+  private readonly camera = new PerspectiveCamera(70, 1, 0.05, 1000);
+  private readonly renderer = new WebGLRenderer({ antialias: true });
+  private readonly ambientLight = new AmbientLight();
+  private readonly sunLight = new DirectionalLight();
+  private readonly brushGroup = new Group();
+  private readonly firstPersonController = new FirstPersonNavigationController();
+  private readonly orbitVisitorController = new OrbitVisitorNavigationController();
+  private readonly brushMeshes = new Map<string, Mesh<BoxGeometry, MeshStandardMaterial[]>>();
+  private readonly materialTextureCache = new Map<string, CachedMaterialTexture>();
+  private readonly controllerContext: RuntimeControllerContext;
+  private resizeObserver: ResizeObserver | null = null;
+  private animationFrame = 0;
+  private previousFrameTime = 0;
+  private container: HTMLElement | null = null;
+  private activeController: NavigationController | null = null;
+  private runtimeScene: RuntimeSceneDefinition | null = null;
+  private runtimeMessageHandler: ((message: string | null) => void) | null = null;
+  private firstPersonTelemetryHandler: ((telemetry: FirstPersonTelemetry | null) => void) | null = null;
+  private currentRuntimeMessage: string | null = null;
+  private currentFirstPersonTelemetry: FirstPersonTelemetry | null = null;
+
+  constructor() {
+    this.scene.add(this.ambientLight);
+    this.scene.add(this.sunLight);
+    this.scene.add(this.brushGroup);
+    this.renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
+
+    this.controllerContext = {
+      camera: this.camera,
+      domElement: this.renderer.domElement,
+      getRuntimeScene: () => {
+        if (this.runtimeScene === null) {
+          throw new Error("Runtime scene has not been loaded.");
+        }
+
+        return this.runtimeScene;
+      },
+      setRuntimeMessage: (message) => {
+        if (message === this.currentRuntimeMessage) {
+          return;
+        }
+
+        this.currentRuntimeMessage = message;
+        this.runtimeMessageHandler?.(message);
+      },
+      setFirstPersonTelemetry: (telemetry) => {
+        this.currentFirstPersonTelemetry = telemetry;
+        this.firstPersonTelemetryHandler?.(telemetry);
+      }
+    };
+  }
+
+  mount(container: HTMLElement) {
+    this.container = container;
+    container.appendChild(this.renderer.domElement);
+    this.resize();
+
+    this.resizeObserver = new ResizeObserver(() => {
+      this.resize();
+    });
+    this.resizeObserver.observe(container);
+
+    this.previousFrameTime = performance.now();
+    this.render();
+  }
+
+  loadScene(runtimeScene: RuntimeSceneDefinition) {
+    this.runtimeScene = runtimeScene;
+    this.applyWorld(runtimeScene);
+    this.rebuildBrushMeshes(runtimeScene.brushes);
+  }
+
+  setNavigationMode(mode: RuntimeNavigationMode) {
+    if (this.runtimeScene === null) {
+      return;
+    }
+
+    const nextController = mode === "firstPerson" ? this.firstPersonController : this.orbitVisitorController;
+
+    if (this.activeController?.id === nextController.id) {
+      return;
+    }
+
+    if (this.activeController === this.firstPersonController && this.currentFirstPersonTelemetry !== null && nextController === this.orbitVisitorController) {
+      this.orbitVisitorController.setFocusPoint(this.currentFirstPersonTelemetry.feetPosition);
+    }
+
+    this.activeController?.deactivate(this.controllerContext);
+    this.activeController = nextController;
+    this.activeController.activate(this.controllerContext);
+  }
+
+  setRuntimeMessageHandler(handler: ((message: string | null) => void) | null) {
+    this.runtimeMessageHandler = handler;
+  }
+
+  setFirstPersonTelemetryHandler(handler: ((telemetry: FirstPersonTelemetry | null) => void) | null) {
+    this.firstPersonTelemetryHandler = handler;
+  }
+
+  dispose() {
+    if (this.animationFrame !== 0) {
+      cancelAnimationFrame(this.animationFrame);
+      this.animationFrame = 0;
+    }
+
+    this.activeController?.deactivate(this.controllerContext);
+    this.activeController = null;
+    this.resizeObserver?.disconnect();
+    this.resizeObserver = null;
+    this.clearBrushMeshes();
+
+    for (const cachedTexture of this.materialTextureCache.values()) {
+      cachedTexture.texture.dispose();
+    }
+
+    this.materialTextureCache.clear();
+    this.renderer.dispose();
+
+    if (this.container !== null && this.container.contains(this.renderer.domElement)) {
+      this.container.removeChild(this.renderer.domElement);
+    }
+
+    this.container = null;
+  }
+
+  private applyWorld(runtimeScene: RuntimeSceneDefinition) {
+    this.scene.background = new Color(runtimeScene.world.background.colorHex);
+    this.ambientLight.color.set(runtimeScene.world.ambientLight.colorHex);
+    this.ambientLight.intensity = runtimeScene.world.ambientLight.intensity;
+    this.sunLight.color.set(runtimeScene.world.sunLight.colorHex);
+    this.sunLight.intensity = runtimeScene.world.sunLight.intensity;
+    this.sunLight.position
+      .set(
+        runtimeScene.world.sunLight.direction.x,
+        runtimeScene.world.sunLight.direction.y,
+        runtimeScene.world.sunLight.direction.z
+      )
+      .normalize()
+      .multiplyScalar(18);
+  }
+
+  private rebuildBrushMeshes(brushes: RuntimeBoxBrushInstance[]) {
+    this.clearBrushMeshes();
+
+    for (const brush of brushes) {
+      const geometry = new BoxGeometry(brush.size.x, brush.size.y, brush.size.z);
+      applyBoxBrushFaceUvsToGeometry(geometry, brush);
+
+      const materials = [
+        this.createFaceMaterial(brush.faces.posX.material),
+        this.createFaceMaterial(brush.faces.negX.material),
+        this.createFaceMaterial(brush.faces.posY.material),
+        this.createFaceMaterial(brush.faces.negY.material),
+        this.createFaceMaterial(brush.faces.posZ.material),
+        this.createFaceMaterial(brush.faces.negZ.material)
+      ];
+
+      const mesh = new Mesh(geometry, materials);
+      mesh.position.set(brush.center.x, brush.center.y, brush.center.z);
+      this.brushGroup.add(mesh);
+      this.brushMeshes.set(brush.id, mesh);
+    }
+  }
+
+  private createFaceMaterial(material: RuntimeBoxBrushInstance["faces"]["posX"]["material"]): MeshStandardMaterial {
+    if (material === null) {
+      return new MeshStandardMaterial({
+        color: FALLBACK_FACE_COLOR,
+        roughness: 0.9,
+        metalness: 0.05
+      });
+    }
+
+    return new MeshStandardMaterial({
+      color: 0xffffff,
+      map: this.getOrCreateTexture(material),
+      roughness: 0.92,
+      metalness: 0.02
+    });
+  }
+
+  private getOrCreateTexture(material: NonNullable<RuntimeBoxBrushInstance["faces"]["posX"]["material"]>) {
+    const signature = createStarterMaterialSignature(material);
+    const cachedTexture = this.materialTextureCache.get(material.id);
+
+    if (cachedTexture !== undefined && cachedTexture.signature === signature) {
+      return cachedTexture.texture;
+    }
+
+    cachedTexture?.texture.dispose();
+
+    const texture = createStarterMaterialTexture(material);
+    this.materialTextureCache.set(material.id, {
+      signature,
+      texture
+    });
+
+    return texture;
+  }
+
+  private clearBrushMeshes() {
+    for (const mesh of this.brushMeshes.values()) {
+      this.brushGroup.remove(mesh);
+      mesh.geometry.dispose();
+
+      for (const material of mesh.material) {
+        material.dispose();
+      }
+    }
+
+    this.brushMeshes.clear();
+  }
+
+  private resize() {
+    if (this.container === null) {
+      return;
+    }
+
+    const width = this.container.clientWidth;
+    const height = this.container.clientHeight;
+
+    if (width === 0 || height === 0) {
+      return;
+    }
+
+    this.camera.aspect = width / height;
+    this.camera.updateProjectionMatrix();
+    this.renderer.setSize(width, height, false);
+  }
+
+  private render = () => {
+    this.animationFrame = window.requestAnimationFrame(this.render);
+
+    const now = performance.now();
+    const dt = Math.min((now - this.previousFrameTime) / 1000, 1 / 20);
+    this.previousFrameTime = now;
+
+    this.activeController?.update(dt);
+    this.renderer.render(this.scene, this.camera);
+  };
+}
diff --git a/src/runtime-three/runtime-scene-build.ts b/src/runtime-three/runtime-scene-build.ts
new file mode 100644
index 00000000..3a02f921
--- /dev/null
+++ b/src/runtime-three/runtime-scene-build.ts
@@ -0,0 +1,221 @@
+import type { Vec3 } from "../core/vector";
+import type { BoxBrush, BoxFaceId, FaceUvState } from "../document/brushes";
+import type { SceneDocument, WorldSettings } from "../document/scene-document";
+import { getPrimaryPlayerStartEntity } from "../entities/entity-instances";
+import { getBoxBrushBounds } from "../geometry/box-brush";
+import { cloneMaterialDef, type MaterialDef } from "../materials/starter-material-library";
+import { cloneFaceUvState } from "../document/brushes";
+
+export type RuntimeNavigationMode = "firstPerson" | "orbitVisitor";
+
+export interface RuntimeBrushFace {
+  materialId: string | null;
+  material: MaterialDef | null;
+  uv: FaceUvState;
+}
+
+export interface RuntimeBoxBrushInstance {
+  id: string;
+  kind: "box";
+  center: Vec3;
+  size: Vec3;
+  faces: Record<BoxFaceId, RuntimeBrushFace>;
+}
+
+export interface RuntimeBoxCollider {
+  kind: "box";
+  brushId: string;
+  min: Vec3;
+  max: Vec3;
+}
+
+export interface RuntimeSceneBounds {
+  min: Vec3;
+  max: Vec3;
+  center: Vec3;
+  size: Vec3;
+}
+
+export interface RuntimePlayerStart {
+  entityId: string;
+  position: Vec3;
+  yawDegrees: number;
+}
+
+export interface RuntimeSpawnPoint {
+  source: "playerStart" | "fallback";
+  entityId: string | null;
+  position: Vec3;
+  yawDegrees: number;
+}
+
+export interface RuntimeSceneDefinition {
+  world: WorldSettings;
+  brushes: RuntimeBoxBrushInstance[];
+  colliders: RuntimeBoxCollider[];
+  sceneBounds: RuntimeSceneBounds | null;
+  playerStart: RuntimePlayerStart | null;
+  spawn: RuntimeSpawnPoint;
+}
+
+function cloneVec3(vector: Vec3): Vec3 {
+  return {
+    x: vector.x,
+    y: vector.y,
+    z: vector.z
+  };
+}
+
+function buildRuntimeBrush(brush: BoxBrush, document: SceneDocument): RuntimeBoxBrushInstance {
+  return {
+    id: brush.id,
+    kind: "box",
+    center: cloneVec3(brush.center),
+    size: cloneVec3(brush.size),
+    faces: {
+      posX: {
+        materialId: brush.faces.posX.materialId,
+        material: brush.faces.posX.materialId === null ? null : cloneMaterialDef(document.materials[brush.faces.posX.materialId]),
+        uv: cloneFaceUvState(brush.faces.posX.uv)
+      },
+      negX: {
+        materialId: brush.faces.negX.materialId,
+        material: brush.faces.negX.materialId === null ? null : cloneMaterialDef(document.materials[brush.faces.negX.materialId]),
+        uv: cloneFaceUvState(brush.faces.negX.uv)
+      },
+      posY: {
+        materialId: brush.faces.posY.materialId,
+        material: brush.faces.posY.materialId === null ? null : cloneMaterialDef(document.materials[brush.faces.posY.materialId]),
+        uv: cloneFaceUvState(brush.faces.posY.uv)
+      },
+      negY: {
+        materialId: brush.faces.negY.materialId,
+        material: brush.faces.negY.materialId === null ? null : cloneMaterialDef(document.materials[brush.faces.negY.materialId]),
+        uv: cloneFaceUvState(brush.faces.negY.uv)
+      },
+      posZ: {
+        materialId: brush.faces.posZ.materialId,
+        material: brush.faces.posZ.materialId === null ? null : cloneMaterialDef(document.materials[brush.faces.posZ.materialId]),
+        uv: cloneFaceUvState(brush.faces.posZ.uv)
+      },
+      negZ: {
+        materialId: brush.faces.negZ.materialId,
+        material: brush.faces.negZ.materialId === null ? null : cloneMaterialDef(document.materials[brush.faces.negZ.materialId]),
+        uv: cloneFaceUvState(brush.faces.negZ.uv)
+      }
+    }
+  };
+}
+
+function buildRuntimeCollider(brush: BoxBrush): RuntimeBoxCollider {
+  const bounds = getBoxBrushBounds(brush);
+
+  return {
+    kind: "box",
+    brushId: brush.id,
+    min: cloneVec3(bounds.min),
+    max: cloneVec3(bounds.max)
+  };
+}
+
+function combineColliderBounds(colliders: RuntimeBoxCollider[]): RuntimeSceneBounds | null {
+  if (colliders.length === 0) {
+    return null;
+  }
+
+  const min = cloneVec3(colliders[0].min);
+  const max = cloneVec3(colliders[0].max);
+
+  for (const collider of colliders.slice(1)) {
+    min.x = Math.min(min.x, collider.min.x);
+    min.y = Math.min(min.y, collider.min.y);
+    min.z = Math.min(min.z, collider.min.z);
+    max.x = Math.max(max.x, collider.max.x);
+    max.y = Math.max(max.y, collider.max.y);
+    max.z = Math.max(max.z, collider.max.z);
+  }
+
+  return {
+    min,
+    max,
+    center: {
+      x: (min.x + max.x) * 0.5,
+      y: (min.y + max.y) * 0.5,
+      z: (min.z + max.z) * 0.5
+    },
+    size: {
+      x: max.x - min.x,
+      y: max.y - min.y,
+      z: max.z - min.z
+    }
+  };
+}
+
+function buildFallbackSpawn(sceneBounds: RuntimeSceneBounds | null): RuntimeSpawnPoint {
+  if (sceneBounds === null) {
+    return {
+      source: "fallback",
+      entityId: null,
+      position: {
+        x: 0,
+        y: 0,
+        z: -4
+      },
+      yawDegrees: 0
+    };
+  }
+
+  return {
+    source: "fallback",
+    entityId: null,
+    position: {
+      x: sceneBounds.center.x,
+      y: sceneBounds.max.y + 0.1,
+      z: sceneBounds.max.z + 3
+    },
+    yawDegrees: 180
+  };
+}
+
+export function buildRuntimeSceneFromDocument(document: SceneDocument): RuntimeSceneDefinition {
+  const brushes = Object.values(document.brushes).map((brush) => buildRuntimeBrush(brush, document));
+  const colliders = Object.values(document.brushes).map((brush) => buildRuntimeCollider(brush));
+  const sceneBounds = combineColliderBounds(colliders);
+  const playerStartEntity = getPrimaryPlayerStartEntity(document.entities);
+  const playerStart =
+    playerStartEntity === null
+      ? null
+      : {
+          entityId: playerStartEntity.id,
+          position: cloneVec3(playerStartEntity.position),
+          yawDegrees: playerStartEntity.yawDegrees
+        };
+
+  return {
+    world: {
+      background: {
+        ...document.world.background
+      },
+      ambientLight: {
+        ...document.world.ambientLight
+      },
+      sunLight: {
+        ...document.world.sunLight,
+        direction: cloneVec3(document.world.sunLight.direction)
+      }
+    },
+    brushes,
+    colliders,
+    sceneBounds,
+    playerStart,
+    spawn:
+      playerStart === null
+        ? buildFallbackSpawn(sceneBounds)
+        : {
+            source: "playerStart",
+            entityId: playerStart.entityId,
+            position: cloneVec3(playerStart.position),
+            yawDegrees: playerStart.yawDegrees
+          }
+  };
+}