feat(model): 双协议 LLM Provider（AnthropicChNativeAdapter /v1/messages + tool_use.input→Args 直接映射 + 流式重组）+ Provider 感知工厂/路由 + LLM_PROVIDER/anthropic 配置（OpenAI 兼容保留）

internal/runtime/model/fallback.go

@@ -29,16 +29,10 @@ func NewChain(steps ...Step) *Chain {
 // NewOpenAIChatChain builds a fallback chain from a single supplier config: the
 // primary model first, then cfg.Fallback (when set and distinct), both served
 // by an OpenAIChatAdapter against the same OpenAI-compatible endpoint. It
-// returns ErrNoModel when no base URL or primary model is configured.
+// delegates to the provider-aware builder so the OpenAI path and the factory stay
+// in sync. It returns ErrNoModel when no base URL or primary model is configured.
 func NewOpenAIChatChain(cfg config.LLMConfig, opts ...OpenAIOption) (*Chain, error) {
-	if cfg.BaseURL == "" || cfg.Model == "" {
-		return nil, ErrNoModel
-	}
-	steps := []Step{{Model: cfg.Model, Adapter: NewOpenAIChat(cfg, opts...)}}
-	if cfg.Fallback != "" && cfg.Fallback != cfg.Model {
-		steps = append(steps, Step{Model: cfg.Fallback, Adapter: NewOpenAIChat(cfg, opts...)})
-	}
-	return NewChain(steps...), nil
+	return newOpenAIChain(cfg, opts...)
 }
 
 // Name returns the chain identifier.