feat: 多专业小模型+路由模型系统 MVP（mock 全链路 + FastAPI 网关 + 论文调研）

gateway/__init__.py

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+"""API 网关：FastAPI 服务。"""␍

gateway/api.py

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+"""FastAPI 网关：对外提供 /chat /health /metrics 接口。
+
+启动：
+    uvicorn gateway.api:app --host 0.0.0.0 --port 8000
+或：
+    python -m gateway.api
+
+依赖：fastapi, uvicorn, pydantic（见 requirements.txt）
+"""
+from __future__ import annotations
+
+from typing import List, Optional
+
+from pydantic import BaseModel, Field
+
+from router_system.config import load_config
+from router_system.router import Router, build_router
+
+# ---- 全局单例 ----
+_router: Optional[Router] = None
+
+
+def get_router() -> Router:
+    global _router
+    if _router is None:
+        _router = build_router()
+    return _router
+
+
+# ---- 请求/响应模型 ----
+class QueryRequest(BaseModel):
+    query: str = Field(..., min_length=1, max_length=8000, description="用户查询")
+
+
+class QueryResponse(BaseModel):
+    response: str
+    domain: str
+    difficulty: str
+    confidence: float
+    upgraded: bool
+    quality_score: float
+    model_used: str
+    route: List[str]
+    latency_ms: float
+    cache_hit: bool
+    cache_level: Optional[str]
+    cost_est: float
+    error: Optional[str] = None
+
+
+class HealthResponse(BaseModel):
+    status: str
+    domains: List[str]
+    classifier: str
+    judge: str
+    fallback: str
+
+
+# ---- FastAPI 应用 ----
+try:
+    from fastapi import FastAPI
+
+    app = FastAPI(
+        title="Multi-Expert Router API",
+        description="多专业小模型 + 路由模型系统（MVP）",
+        version="0.1.0",
+    )
+
+    @app.get("/health", response_model=HealthResponse, tags=["system"])
+    async def health():
+        return get_router().health()
+
+    @app.post("/chat", response_model=QueryResponse, tags=["chat"])
+    async def chat(req: QueryRequest):
+        result = await get_router().route(req.query)
+        return QueryResponse(**result.to_dict())
+
+    @app.get("/metrics", tags=["system"])
+    async def metrics():
+        r = get_router()
+        return {
+            "router": r.stats.summary(),
+            "cache": r.cache.stats(),
+        }
+
+except ImportError:
+    # fastapi 未安装时，提供 CLI 入口提示
+    app = None
+    print("[gateway] 未安装 fastapi，请执行: pip install -r requirements.txt")
+
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run("gateway.api:app", host="0.0.0.0", port=8000, reload=False)␍