Refactor assistant configuration management and update documentation

- Removed legacy agent profile settings from the .env.example and README, streamlining the configuration process.
- Introduced a new local YAML configuration adapter for assistant settings, allowing for easier management of assistant profiles.
- Updated backend integration documentation to clarify the behavior of assistant config sourcing based on backend URL settings.
- Adjusted various service implementations to directly utilize API keys from the new configuration structure.
- Enhanced test coverage for the new local YAML adapter and its integration with backend services.

engine/README.md

@@ -1,6 +1,6 @@
-# py-active-call-cc
+# Realtime Agent Studio Engine
 
-Python Active-Call: real-time audio streaming with WebSocket and WebRTC.
+This repo contains a Python 3.11+ codebase for building low-latency realtime human-agent interaction pipelines (capture, stream, and process audio) using WebSockets or WebRTC.
 
 This repo contains a Python 3.11+ codebase for building low-latency voice
 pipelines (capture, stream, and process audio) using WebRTC and WebSockets.
@@ -14,35 +14,11 @@ It is currently in an early, experimental stage.
 uvicorn app.main:app --reload --host 0.0.0.0 --port 8000
 ```
 
-使用 agent profile（推荐）
-
-```
-python -m app.main --agent-profile default
-```
-
-使用指定 YAML
-
-```
-python -m app.main --agent-config config/agents/default.yaml
-```
-
-Agent 配置路径优先级
-1. `--agent-config`
-2. `--agent-profile`（映射到 `config/agents/<profile>.yaml`）
-3. `AGENT_CONFIG_PATH`
-4. `AGENT_PROFILE`
-5. `config/agents/default.yaml`（若存在）
-
 说明
-- Agent 相关配置是严格模式：YAML 缺少必须项会直接报错，不会回退到 `.env` 或代码默认值。
-- 如果要引用环境变量，请在 YAML 显式写 `${ENV_VAR}`。
-- `siliconflow` 独立 section 已移除；请在 `agent.llm / agent.tts / agent.asr` 内通过 `provider`、`api_key`、`api_url`、`model` 配置。
-- `agent.tts.provider` 现支持 `dashscope`（Realtime 协议，非 OpenAI-compatible）；默认 URL 为 `wss://dashscope.aliyuncs.com/api-ws/v1/realtime`，默认模型为 `qwen3-tts-flash-realtime`。
-- `agent.tts.dashscope_mode`（兼容旧写法 `agent.tts.mode`）支持 `commit | server_commit`，且仅在 `provider=dashscope` 时生效：
-  - `commit`：Engine 先按句切分，再逐句提交给 DashScope。
-  - `server_commit`：Engine 不再逐句切分，由 DashScope 对整段文本自行切分。
-- 现在支持在 Agent YAML 中配置 `agent.tools`（列表），用于声明运行时可调用工具。
-- 工具配置示例见 `config/agents/tools.yaml`。
+- 启动阶段不再通过参数加载 Agent YAML。
+- 会话阶段统一按 `assistant_id` 拉取运行时配置：
+  - 有 `BACKEND_URL`：从 backend API 获取。
+  - 无 `BACKEND_URL`（或 `BACKEND_MODE=disabled`）：从 `ASSISTANT_LOCAL_CONFIG_DIR/<assistant_id>.yaml` 获取。
 
 ## Backend Integration
 
@@ -50,6 +26,7 @@ Engine runtime now supports adapter-based backend integration:
 
 - `BACKEND_MODE=auto|http|disabled`
 - `BACKEND_URL` + `BACKEND_TIMEOUT_SEC`
+- `ASSISTANT_LOCAL_CONFIG_DIR` (default `engine/config/agents`)
 - `HISTORY_ENABLED=true|false`
 
 Behavior:
@@ -58,6 +35,16 @@ Behavior:
 - `http`: force HTTP backend; falls back to engine-only mode when URL is missing.
 - `disabled`: force engine-only mode (no backend calls).
 
+Assistant config source behavior:
+
+- If `BACKEND_URL` is configured and backend mode is enabled, assistant config is loaded from backend API.
+- If `BACKEND_URL` is empty (or backend mode is disabled), assistant config is loaded from local YAML.
+
+Local assistant YAML example:
+
+- File path: `engine/config/agents/<assistant_id>.yaml`
+- Runtime still requires WebSocket query param `assistant_id`; it must match the local file name.
+
 History write path is now asynchronous and buffered per session:
 
 - `HISTORY_QUEUE_MAX_SIZE`
@@ -84,3 +71,6 @@ python mic_client.py
 `/ws` uses a strict `v1` JSON control protocol with binary PCM audio frames.
 
 See `docs/ws_v1_schema.md`.
+
+# Reference
+* [active-call](https://github.com/restsend/active-call)