连接 Client — Downcity City SDK Docs

User City 有两条常用通路：

client.ai.* 调内置 AIService
client.service(id).action(name).invoke() 调自定义 Service 或服务 Service

import { City } from "@downcity/city";

const client = new City({
  role: "user",
  city_url: "http://127.0.0.1:43127",
  town_id: "town_downcity",
  user_token: "ub_xxx",
});

// AI Service — SDK 通路
const msg = await client.ai.text({ prompt: "hello", model: "deepseek-v4-flash" });
const stream = await client.ai.stream({ prompt: "hello" });

// AI Service — OpenAI 通路（用 OpenAI SDK 直接调）
import OpenAI from "openai";
const openai = new OpenAI({ baseURL: "http://127.0.0.1:43127/v1/ai", apiKey: "ub_xxx" });
await openai.chat.completions.create({ model: "kimi-k2.6", messages: [...] });

// 自定义 Service
const result = await client.service("translate").action("zh2en").invoke({ text: "你好" });

// GET action（如轮询 OAuth 结果）
const oauth = await client.service("accounts").get("oauth/result", { state: "state_xxx" });

创建 town、暂停 town、签发 user_token 和维护 Runtime env 都属于可信环境动作，用 Admin City 完成，不放到产品前端。