refactor : FastAPI 懒加载单例，消除模块级副作用

- import astrai.inference 不再在模块加载时创建 FastAPI 实例
- 路由移至 APIRouter；get_app() 首次调用时懒构造单例
- _create_engine 和 run_server 的 param_path 改为必填
- 更新测试改用 get_app() 替代模块级 app

tests/inference/conftest.py

@@ -5,21 +5,22 @@ from unittest.mock import MagicMock
 import pytest
 from fastapi.testclient import TestClient
 
-from astrai.inference import app
+from astrai.inference import get_app
 
 
 @pytest.fixture
 def client():
     """Provide a test client for the FastAPI app."""
-    app.state.server_config = {
+    _app = get_app()
+    _app.state.server_config = {
         "device": "cpu",
         "dtype": "bfloat16",
         "param_path": None,
         "max_batch_size": 1,
         "_test": True,
     }
-    app.state.engine = None
-    return TestClient(app)
+    _app.state.engine = None
+    return TestClient(_app)
 
 
 @pytest.fixture
@@ -49,5 +50,5 @@ def mock_engine():
 @pytest.fixture
 def loaded_model(client, mock_engine):
     """Simulate that the engine is loaded."""
-    app.state.engine = mock_engine
+    get_app().state.engine = mock_engine
     return mock_engine

tests/inference/test_server.py

@@ -2,12 +2,12 @@
 
 import pytest
 
-from astrai.inference import app
+from astrai.inference import get_app
 
 
 def test_health_no_model(client):
     """GET /health should return 200 even when engine not loaded."""
-    app.state.engine = None
+    get_app().state.engine = None
     response = client.get("/health")
     assert response.status_code == 200
     data = response.json()
@@ -30,7 +30,7 @@ def test_chat_completions_non_stream(client, loaded_model):
     async def async_gen():
         yield "Assistant reply"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/chat/completions",
@@ -56,7 +56,7 @@ def test_chat_completions_stream(client, loaded_model):
         yield "cumulative1"
         yield "cumulative2"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/chat/completions",
@@ -83,7 +83,7 @@ def test_messages_non_stream(client, loaded_model):
     async def async_gen():
         yield "Assistant reply"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/messages",
@@ -111,7 +111,7 @@ def test_messages_stream(client, loaded_model):
         yield "cumulative1"
         yield "cumulative2"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/messages",
@@ -141,7 +141,7 @@ def test_messages_with_system(client, loaded_model):
     async def async_gen():
         yield "Reply"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/messages",
@@ -165,7 +165,7 @@ def test_chat_completions_stop_sequence(client, loaded_model):
         yield "X"
         yield "world"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/chat/completions",
@@ -191,7 +191,7 @@ def test_chat_completions_stop_sequence_stream(client, loaded_model):
         yield "X"
         yield "world"
 
-    app.state.engine = loaded_model
+    get_app().state.engine = loaded_model
     loaded_model.generate_async.return_value = async_gen()
     response = client.post(
         "/v1/chat/completions",