feat(strategy): M8.3 策略模型 + /api/strategies（命名配置资产，可展开为 ResearchSpec）

- StrategyDefinition：universe/factors/selection/rebalance/costs/portfolio +
  price_adjustment（除 period 外完整策略定义）；to_research_spec(period) 展开为标准 Spec
- strategy 表（migration e1f2a3b4c5d6，MySQL 已应用；name 唯一）+ StrategyRepository
- /api/strategies：POST/GET/DELETE + POST /{id}/expand（period+initial_capital → ResearchSpec）
- tests/test_strategies.py（repo CRUD/同名/expand、API CRUD/400/404）；全量 pytest 通过

backend/app/infrastructure/persistence/migrations/versions/e1f2a3b4c5d6_strategy_table.py

@@ -0,0 +1,38 @@
+"""strategy 表（M8.3 策略持久化）
+
+Revision ID: e1f2a3b4c5d6
+Revises: d8e0b2f3c4d5
+Create Date: 2026-09-09
+
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "e1f2a3b4c5d6"
+down_revision: str | None = "d8e0b2f3c4d5"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "strategy",
+        sa.Column("id", sa.String(length=32), nullable=False),
+        sa.Column("name", sa.String(length=64), nullable=False),
+        sa.Column("description", sa.String(length=300), nullable=False),
+        sa.Column("spec_type", sa.String(length=16), nullable=False),
+        sa.Column("config_json", sa.Text(), nullable=False),
+        sa.Column("version", sa.String(length=16), nullable=False),
+        sa.Column("created_at", sa.DateTime(), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("name", name="uq_strategy_name"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("strategy")

backend/app/infrastructure/persistence/sqlalchemy/models/__init__.py

@@ -30,3 +30,6 @@ from app.infrastructure.persistence.sqlalchemy.models.signal import (  # noqa: F
     SignalEventModel,
     SignalSnapshotModel,
 )
+from app.infrastructure.persistence.sqlalchemy.models.strategy import (  # noqa: F401
+    StrategyModel,
+)

backend/app/infrastructure/persistence/sqlalchemy/models/strategy.py

@@ -0,0 +1,22 @@
+"""strategy 表（M8.3）。"""
+
+from __future__ import annotations
+
+from datetime import datetime
+
+from sqlalchemy import DateTime, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.infrastructure.persistence.sqlalchemy.base import Base
+
+
+class StrategyModel(Base):
+    __tablename__ = "strategy"
+
+    id: Mapped[str] = mapped_column(String(32), primary_key=True)
+    name: Mapped[str] = mapped_column(String(64), unique=True)
+    description: Mapped[str] = mapped_column(String(300), default="")
+    spec_type: Mapped[str] = mapped_column(String(16), default="backtest")
+    config_json: Mapped[str] = mapped_column(Text)
+    version: Mapped[str] = mapped_column(String(16), default="1")
+    created_at: Mapped[datetime] = mapped_column(DateTime)

backend/app/infrastructure/persistence/sqlalchemy/repositories/strategy_impl.py

@@ -0,0 +1,86 @@
+"""策略 Repository 的 SQLAlchemy 实现（M8.3）。
+
+config 以 JSON 存（StrategyDefinition.model_dump）；读取时重建实体。
+"""
+
+from __future__ import annotations
+
+import json
+from datetime import datetime
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
+from app.domain.entities.strategy import StrategyDefinition
+from app.infrastructure.persistence.sqlalchemy.models.strategy import StrategyModel
+
+
+class SqlAlchemyStrategyRepository:
+    def __init__(self, session: Session) -> None:
+        self._session = session
+
+    def save(self, definition: StrategyDefinition) -> StrategyDefinition:
+        if not definition.id:
+            raise ValueError("需要 id（由调用方生成）")
+        dup = self._session.scalar(
+            select(StrategyModel).where(StrategyModel.name == definition.name).limit(1)
+        )
+        if dup is not None and dup.id != definition.id:
+            raise ValueError(f"策略名已存在：{definition.name}")
+        now = definition.created_at or datetime.now()
+        row = self._session.get(StrategyModel, definition.id)
+        config_json = json.dumps(definition.model_dump(exclude={"id", "created_at"}), ensure_ascii=False)
+        if row is None:
+            self._session.add(
+                StrategyModel(
+                    id=definition.id,
+                    name=definition.name,
+                    description=definition.description,
+                    spec_type=definition.spec_type,
+                    config_json=config_json,
+                    version=definition.version,
+                    created_at=now,
+                )
+            )
+        else:
+            row.name = definition.name
+            row.description = definition.description
+            row.spec_type = definition.spec_type
+            row.config_json = config_json
+            row.version = definition.version
+        self._session.flush()
+        return definition
+
+    def get(self, strategy_id: str) -> StrategyDefinition | None:
+        row = self._session.get(StrategyModel, strategy_id)
+        return _to_entity(row) if row else None
+
+    def get_by_name(self, name: str) -> StrategyDefinition | None:
+        row = self._session.scalar(
+            select(StrategyModel).where(StrategyModel.name == name).limit(1)
+        )
+        return _to_entity(row) if row else None
+
+    def list(self) -> list[StrategyDefinition]:
+        rows = self._session.scalars(
+            select(StrategyModel).order_by(StrategyModel.name)
+        ).all()
+        return [_to_entity(r) for r in rows]
+
+    def delete(self, strategy_id: str) -> bool:
+        row = self._session.get(StrategyModel, strategy_id)
+        if row is None:
+            return False
+        self._session.delete(row)
+        return True
+
+
+def _to_entity(row: StrategyModel) -> StrategyDefinition:
+    data = json.loads(row.config_json)
+    # 列字段由 DB 行回填，避免与 config_json 重复
+    for key in ("name", "version", "description", "spec_type"):
+        data.pop(key, None)
+    return StrategyDefinition(
+        id=row.id, name=row.name, version=row.version,
+        created_at=row.created_at, **data,
+    )