chore: import upstream snapshot with attribution

examples/integrations/mcp-apps/threejs-server/README.md

@@ -0,0 +1,110 @@
+# Example: Three.js App
+
+![Screenshot](screenshot.png)
+
+Interactive 3D scene renderer using Three.js. Demonstrates streaming code preview and full MCP App integration.
+
+## Features
+
+- **Interactive 3D Rendering**: Execute JavaScript code to create and animate Three.js scenes
+- **Streaming Preview**: See the scene build in real-time as code is being written
+- **Built-in Helpers**: Pre-configured `OrbitControls`, post-processing effects (bloom), and render passes
+- **Documentation Tool**: `learn_threejs` provides API docs and code examples on demand
+
+## Running
+
+1. Install dependencies:
+
+   ```bash
+   npm install
+   ```
+
+2. Build and start the server:
+
+   ```bash
+   npm run start:http  # for Streamable HTTP transport
+   # OR
+   npm run start:stdio  # for stdio transport
+   ```
+
+3. View using the [`basic-host`](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-host) example or another MCP Apps-compatible host.
+
+### Tool Input
+
+To test the example, copy the contents of [`test-input.json`](test-input.json) into the tool input field in `basic-host`.
+
+The test input creates a simple scene with a rotating cube:
+
+```javascript
+const scene = new THREE.Scene();
+const camera = new THREE.PerspectiveCamera(60, width / height, 0.1, 100);
+camera.position.set(2, 2, 2);
+
+const renderer = new THREE.WebGLRenderer({ canvas, antialias: true });
+renderer.setSize(width, height);
+renderer.shadowMap.enabled = true;
+
+const cube = new THREE.Mesh(
+  new THREE.BoxGeometry(),
+  new THREE.MeshStandardMaterial({ color: 0x00ff88 }),
+);
+cube.castShadow = true;
+cube.position.y = 0.5;
+scene.add(cube);
+
+const floor = new THREE.Mesh(
+  new THREE.PlaneGeometry(5, 5),
+  new THREE.MeshStandardMaterial({ color: 0x222233 }),
+);
+floor.rotation.x = -Math.PI / 2;
+floor.receiveShadow = true;
+scene.add(floor);
+
+const light = new THREE.DirectionalLight(0xffffff, 2);
+light.position.set(3, 5, 3);
+light.castShadow = true;
+scene.add(light);
+scene.add(new THREE.AmbientLight(0x404040));
+
+function animate() {
+  requestAnimationFrame(animate);
+  cube.rotation.y += 0.01;
+  renderer.render(scene, camera);
+}
+animate();
+```
+
+#### Available Three.js Globals
+
+When writing custom code, these globals are available:
+
+```javascript
+THREE; // Three.js library
+canvas; // Pre-created canvas element
+width; // Canvas width
+height; // Canvas height
+OrbitControls; // Camera controls
+EffectComposer; // Post-processing composer
+RenderPass; // Render pass
+UnrealBloomPass; // Bloom effect
+```
+
+## Architecture
+
+### Server (`server.ts`)
+
+Exposes two tools:
+
+- `show_threejs_scene` - Renders a 3D scene from JavaScript code
+- `learn_threejs` - Returns documentation and code examples for Three.js APIs
+
+Supports Streamable HTTP and stdio transports.
+
+### App (`src/threejs-app.tsx`)
+
+React component that:
+
+- Receives tool inputs via the MCP App SDK
+- Displays streaming preview from `toolInputsPartial.code` as code arrives
+- Executes final code from `toolInputs.code` when complete
+- Renders to a pre-created canvas with configurable height