chore: import upstream snapshot with attribution

examples/config-websockets/basic/README.md

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+# config-websockets/basic (Websockets Provider Example)
+
+You can run this example with:
+
+```bash
+npx promptfoo@latest init --example config-websockets/basic
+cd config-websockets/basic
+```
+
+This example shows how to connect promptfoo to a WebSocket-based LLM service.
+
+## Prerequisites
+
+- Node.js ^20.20.0 or >=22.22.0 (Node.js 20 support ends July 30, 2026; Node.js 24 LTS recommended)
+- API keys for LLM providers set as environment variables:
+  - `OPENAI_API_KEY` - Get from [OpenAI API keys page](https://platform.openai.com/api-keys)
+  - `ANTHROPIC_API_KEY` - Get from [Anthropic Console](https://console.anthropic.com/) (optional)
+
+## Quick Start
+
+1. Start the test server (simulates a WebSocket LLM service):
+
+```bash
+cd test-server
+npm install
+node server.js
+```
+
+2. In a new terminal, run the evaluation:
+
+```bash
+promptfoo eval
+```
+
+## Expected Results
+
+This example will:
+
+- Start a mock WebSocket server that simulates an LLM service
+- Connect promptfoo to the WebSocket server using the custom provider
+- Run evaluations through the WebSocket connection
+- Demonstrate how to integrate promptfoo with custom WebSocket-based APIs
+- Save results that can be viewed with `promptfoo view`

examples/config-websockets/basic/promptfooconfig.yaml

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+# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
+description: 'Websocket test'
+
+prompts:
+  - 'Rephrase this in {{language}}: {{body}}'
+  - 'Translate this to conversational {{language}}: {{body}}'
+
+providers:
+  - id: 'ws://localhost:4000'
+    config:
+      messageTemplate: '{"prompt": {{prompt | dump}}, "model": {{model | dump}}}'
+      transformResponse: 'data.output'
+
+tests:
+  - vars:
+      language: French
+      body: Hello world
+  - vars:
+      language: French
+      body: I'm hungry
+  - vars:
+      language: Pirate
+      body: Hello world
+  - vars:
+      language: Pirate
+      body: I'm hungry

examples/config-websockets/basic/test-server/package.json

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+{
+  "name": "websockets",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "MIT",
+  "private": true,
+  "description": "",
+  "dependencies": {
+    "ws": "^8.19.0"
+  }
+}

examples/config-websockets/basic/test-server/server.js

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+const WebSocket = require('ws');
+const http = require('http');
+
+const server = http.createServer();
+const wss = new WebSocket.Server({ server });
+
+wss.on('connection', (ws) => {
+  console.log('Client connected');
+
+  ws.on('message', (message) => {
+    console.log('Received:', message.toString());
+
+    try {
+      const data = JSON.parse(message);
+
+      // Simulate some processing time
+      setTimeout(() => {
+        const response = {
+          output: `Processed: ${data.prompt} at ${new Date().toISOString()}`,
+          model: data.model || 'default',
+          timestamp: new Date().toISOString(),
+        };
+
+        ws.send(JSON.stringify(response));
+      }, 1000);
+    } catch (error) {
+      console.error('Error processing message:', error);
+      ws.send(JSON.stringify({ error: 'Invalid JSON' }));
+    }
+  });
+
+  ws.on('close', () => {
+    console.log('Client disconnected');
+  });
+});
+
+const PORT = process.env.PORT || 4000;
+server.listen(PORT, () => {
+  console.log(`WebSocket server is running on ws://localhost:${PORT}`);
+});