refactor: 重构异步任务系统和计费服务架构

- 重构任务系统：新增 lifecycle (TaskStatus/BillingStatus)、context、application 模块
- 将 video tasks 泛化为 async tasks，支持更通用的异步任务管理
- 新增 Gemini Files 管理模块和管理界面
- 重构 billing 服务：拆分 schema.py 和 service.py
- 新增 candidate 服务模块用于请求候选管理
- 数据库迁移：添加 billing_status、request_id、gemini_file_mappings 表和索引
- 移除废弃的 video_telemetry、task orchestrator 等模块

tests/services/test_video_finalize.py

@@ -0,0 +1,191 @@
+from types import SimpleNamespace
+from typing import Any
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from src.config.settings import config
+from src.core.api_format.conversion.internal_video import VideoStatus
+from src.services.billing.formula_engine import BillingIncompleteError
+from src.services.task.application import TaskApplicationService
+
+
+def _make_task(**overrides: Any) -> SimpleNamespace:
+    task = SimpleNamespace(
+        id="t1",
+        request_id="req-1",
+        user_id="u1",
+        api_key_id="ak1",
+        provider_id="p1",
+        endpoint_id="e1",
+        key_id="k1",
+        external_task_id="ext-1",
+        client_api_format="openai:video",
+        provider_api_format="openai:video",
+        format_converted=False,
+        model="sora",
+        original_request_body={"model": "sora"},
+        duration_seconds=4,
+        resolution="720p",
+        aspect_ratio="16:9",
+        size="1024x1024",
+        retry_count=0,
+        video_size_bytes=None,
+        video_url="https://example.com/v.mp4",
+        video_urls=["https://example.com/v.mp4"],
+        submitted_at=None,
+        completed_at=None,
+        error_code=None,
+        error_message=None,
+        status=VideoStatus.COMPLETED.value,
+        request_metadata={"poll_raw_response": {"foo": "bar"}},
+    )
+    for k, v in overrides.items():
+        setattr(task, k, v)
+    return task
+
+
+def _make_db() -> MagicMock:
+    db = MagicMock()
+
+    user_obj = SimpleNamespace(id="u1")
+    api_key_obj = SimpleNamespace(id="ak1")
+    provider_obj = SimpleNamespace(id="p1", name="prov1")
+    usage_obj = SimpleNamespace(
+        id="usage-1",
+        request_id="req-1",
+        billing_status="settled",  # finalize_submitted already settled
+        request_metadata=None,  # no billing_updated_at yet
+    )
+
+    q_usage = MagicMock()
+    q_usage.filter.return_value.first.return_value = usage_obj
+    q_user = MagicMock()
+    q_user.filter.return_value.first.return_value = user_obj
+    q_key = MagicMock()
+    q_key.filter.return_value.first.return_value = api_key_obj
+    q_provider = MagicMock()
+    q_provider.filter.return_value.first.return_value = provider_obj
+
+    db.query.side_effect = [q_usage, q_user, q_key, q_provider]
+    return db
+
+
+@pytest.mark.asyncio
+async def test_video_finalize_failed_records_cost_zero(monkeypatch: pytest.MonkeyPatch) -> None:
+    db = _make_db()
+    task = _make_task(status=VideoStatus.FAILED.value, error_message="boom")
+
+    monkeypatch.setattr(
+        "src.services.billing.dimension_collector_service.DimensionCollectorService.collect_dimensions",
+        lambda _self, **_kwargs: {"duration_seconds": 4},
+    )
+    monkeypatch.setattr(
+        "src.services.task.application.BillingRuleService.find_rule",
+        lambda *_args, **_kwargs: None,
+    )
+    # Mock update_settled_billing (used by finalize_video_task)
+    update_settled = MagicMock(return_value=True)
+    monkeypatch.setattr(
+        "src.services.task.application.UsageService.update_settled_billing",
+        update_settled,
+    )
+
+    app = TaskApplicationService(db)
+    await app.finalize_video_task(task)
+
+    # billing_snapshot should be written back to task.request_metadata
+    assert task.request_metadata["billing_snapshot"]["cost"] == 0.0
+
+    assert update_settled.call_count == 1
+    kwargs = update_settled.call_args.kwargs
+    assert kwargs["total_cost_usd"] == 0.0
+    assert kwargs["status"] == "failed"
+
+
+@pytest.mark.asyncio
+async def test_video_finalize_completed_no_rule(monkeypatch: pytest.MonkeyPatch) -> None:
+    db = _make_db()
+    task = _make_task(status=VideoStatus.COMPLETED.value)
+
+    monkeypatch.setattr(
+        "src.services.billing.dimension_collector_service.DimensionCollectorService.collect_dimensions",
+        lambda _self, **_kwargs: {"duration_seconds": 4},
+    )
+    monkeypatch.setattr(
+        "src.services.task.application.BillingRuleService.find_rule",
+        lambda *_args, **_kwargs: None,
+    )
+    # Mock update_settled_billing (used by finalize_video_task)
+    update_settled = MagicMock(return_value=True)
+    monkeypatch.setattr(
+        "src.services.task.application.UsageService.update_settled_billing",
+        update_settled,
+    )
+
+    app = TaskApplicationService(db)
+    await app.finalize_video_task(task)
+
+    assert task.request_metadata["billing_snapshot"]["status"] == "no_rule"
+
+    kwargs = update_settled.call_args.kwargs
+    assert kwargs["total_cost_usd"] == 0.0
+    assert kwargs["status"] == "completed"
+
+
+@pytest.mark.asyncio
+async def test_video_finalize_strict_mode_missing_required_marks_failed(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    db = _make_db()
+    task = _make_task(
+        status=VideoStatus.COMPLETED.value,
+        request_metadata={
+            "poll_raw_response": {"foo": "bar"},
+            "billing_rule_snapshot": {
+                "status": "ok",
+                "rule_id": "r1",
+                "rule_name": "video",
+                "scope": "model",
+                "expression": "duration_seconds",
+                "variables": {},
+                "dimension_mappings": {},
+            },
+        },
+    )
+
+    monkeypatch.setattr(
+        "src.services.billing.dimension_collector_service.DimensionCollectorService.collect_dimensions",
+        lambda _self, **_kwargs: {"duration_seconds": None},
+    )
+    # Mock update_settled_billing (used by finalize_video_task)
+    update_settled = MagicMock(return_value=True)
+    monkeypatch.setattr(
+        "src.services.task.application.UsageService.update_settled_billing",
+        update_settled,
+    )
+
+    old = config.billing_strict_mode
+    try:
+        config.billing_strict_mode = True
+        monkeypatch.setattr(
+            "src.services.task.application.FormulaEngine.evaluate",
+            MagicMock(
+                side_effect=BillingIncompleteError(
+                    "Missing required dimensions", missing_required=["duration_seconds"]
+                )
+            ),
+        )
+        app = TaskApplicationService(db)
+        await app.finalize_video_task(task)
+    finally:
+        config.billing_strict_mode = old
+
+    assert task.status == VideoStatus.FAILED.value
+    assert task.video_url is None
+    assert task.video_urls is None
+    assert "billing_incomplete" in (task.error_code or "")
+
+    kwargs = update_settled.call_args.kwargs
+    assert kwargs["total_cost_usd"] == 0.0
+    assert kwargs["status"] == "failed"