refactor(llm): enable hot-reload for model config and client runtime

make LLM task config resolution dynamic in LLMRequest
load model clients on demand from latest config
clear client instance cache on config reload
remove stale module-level model_config usage in llm_api
add hot-reload tests for LLM/config watcher flow

src/llm_models/model_client/base_client.py

@@ -3,11 +3,15 @@ from dataclasses import dataclass
 from abc import ABC, abstractmethod
 from typing import Callable, Any, Optional
 
+from src.common.logger import get_logger
+from src.config.config import config_manager
 from src.config.model_configs import ModelInfo, APIProvider
 from ..payload_content.message import Message
 from ..payload_content.resp_format import RespFormat
 from ..payload_content.tool_option import ToolOption, ToolCall
 
+logger = get_logger("model_client_registry")
+
 
 @dataclass
 class UsageRecord:
@@ -144,6 +148,7 @@ class ClientRegistry:
         """APIProvider.type -> BaseClient的映射表"""
         self.client_instance_cache: dict[str, BaseClient] = {}
         """APIProvider.name -> BaseClient的映射表"""
+        config_manager.register_reload_callback(self.clear_client_instance_cache)
 
     def register_client_class(self, client_type: str):
         """
@@ -169,6 +174,10 @@ class ClientRegistry:
         Returns:
             BaseClient: 注册的API客户端实例
         """
+        from . import ensure_client_type_loaded
+
+        ensure_client_type_loaded(api_provider.client_type)
+
         # 如果强制创建新实例，直接创建不使用缓存
         if force_new:
             if client_class := self.client_registry.get(api_provider.client_type):
@@ -184,5 +193,9 @@ class ClientRegistry:
                 raise KeyError(f"'{api_provider.client_type}' 类型的 Client 未注册")
         return self.client_instance_cache[api_provider.name]
 
+    def clear_client_instance_cache(self) -> None:
+        self.client_instance_cache.clear()
+        logger.info("检测到配置重载，已清空LLM客户端实例缓存")
+
 
 client_registry = ClientRegistry()