feat(signal): M8.1 交易信号引擎（规则 + signal_event 落库 + /api/signals）

- SignalRules（买入 rank 阈值/趋势 MA/动量 + 卖出区间/破位警示）+ SignalEvent
  （BUY/WATCH/SELL，score/price/trigger_reason 可解释）+ SignalResult/Meta
- quant/signal.generate_signals：与选股同一评分引擎取全市场 rank，按规则分类输出
- signal_snapshot/signal_event 表（migration d8e0b2f3c4d5，MySQL 已应用）+ Repo
- SignalService + POST /api/signals（同步+落库）、GET 详情/列表
- tests/test_signals.py（引擎分类/排序/破位不 BUY、service、API 提交读回）；全量 pytest 通过

backend/app/api/deps.py

@@ -11,6 +11,7 @@ from fastapi import Depends
 from sqlalchemy.orm import Session
 
 from app.application.services.selection_service import SelectionService
+from app.application.services.signal_service import SignalService
 from app.domain.repositories.composite import CompositeRepository
 from app.domain.repositories.factor import FactorRepository
 from app.domain.repositories.jobs import ExperimentRepository, JobRepository
@@ -20,6 +21,7 @@ from app.domain.repositories.market import (
     StockRepository,
 )
 from app.domain.repositories.selection import SelectionRepository
+from app.domain.repositories.signal import SignalRepository
 from app.infrastructure.persistence.sqlalchemy.repositories.composite_impl import (
     SqlAlchemyCompositeRepository,
 )
@@ -34,6 +36,9 @@ from app.infrastructure.persistence.sqlalchemy.repositories.market_impl import (
 from app.infrastructure.persistence.sqlalchemy.repositories.selection_impl import (
     SqlAlchemySelectionRepository,
 )
+from app.infrastructure.persistence.sqlalchemy.repositories.signal_impl import (
+    SqlAlchemySignalRepository,
+)
 from app.infrastructure.persistence.sqlalchemy.session import get_session
 from app.quant.engine import LocalEngine, QuantEngine
 from app.quant.service import ResearchService
@@ -65,6 +70,13 @@ def _service_factory(
     return ResearchService(stock_repo, daily_repo, engine)
 
 
+def _signal_service_factory(
+    stock_repo: Annotated[StockRepository, Depends(_stock_repo_factory)],
+    daily_repo: Annotated[DailyBarRepository, Depends(_daily_repo_factory)],
+) -> SignalService:
+    return SignalService(stock_repo, daily_repo)
+
+
 def _selection_service_factory(
     stock_repo: Annotated[StockRepository, Depends(_stock_repo_factory)],
     daily_repo: Annotated[DailyBarRepository, Depends(_daily_repo_factory)],
@@ -86,6 +98,10 @@ def _composite_repo_factory(session: DbSession) -> CompositeRepository:
     return SqlAlchemyCompositeRepository(session)
 
 
+def _signal_repo_factory(session: DbSession) -> SignalRepository:
+    return SqlAlchemySignalRepository(session)
+
+
 StockRepoDep = Annotated[StockRepository, Depends(_stock_repo_factory)]
 DailyRepoDep = Annotated[DailyBarRepository, Depends(_daily_repo_factory)]
 EngineDep = Annotated[QuantEngine, Depends(_engine_factory)]
@@ -94,6 +110,8 @@ SelectionServiceDep = Annotated[SelectionService, Depends(_selection_service_fac
 SelectionRepoDep = Annotated[SelectionRepository, Depends(_selection_repo_factory)]
 FactorRepoDep = Annotated[FactorRepository, Depends(_factor_repo_factory)]
 CompositeRepoDep = Annotated[CompositeRepository, Depends(_composite_repo_factory)]
+SignalRepoDep = Annotated[SignalRepository, Depends(_signal_repo_factory)]
+SignalServiceDep = Annotated[SignalService, Depends(_signal_service_factory)]
 
 
 def _job_repo_factory(session: DbSession):

backend/app/api/router.py

@@ -17,6 +17,7 @@ from app.api import (
     jobs,
     research,
     selections,
+    signals,
     stocks,
 )
 
@@ -27,6 +28,7 @@ api_router.include_router(factors.router)
 api_router.include_router(composites.router)
 api_router.include_router(research.router)
 api_router.include_router(selections.router)
+api_router.include_router(signals.router)
 api_router.include_router(jobs.router)
 api_router.include_router(experiments.router)
 api_router.include_router(agent.router)

backend/app/api/signals.py

@@ -0,0 +1,65 @@
+"""交易信号 API（M8.1）：提交/查询信号（落库可复现）。
+
+POST /api/signals      body: {query: SelectionQuery, rules?: SignalRules}
+GET  /api/signals/{id} 读回某次信号
+GET  /api/signals      历史信号元数据（可过滤 as_of）
+"""
+
+from __future__ import annotations
+
+from datetime import date
+from typing import Annotated
+
+from fastapi import APIRouter, HTTPException, Query
+from pydantic import BaseModel
+
+from app.api.deps import DbSession, SignalRepoDep, SignalServiceDep
+from app.application.services.job_executor import new_id
+from app.domain.entities.selection import SelectionQuery
+from app.domain.entities.signal import SignalMeta, SignalResult, SignalRules
+
+router = APIRouter(prefix="/signals", tags=["signals"])
+
+_AsOfQuery = Annotated[date | None, Query(description="按信号时点过滤")]
+_LimitQuery = Annotated[int, Query(ge=1, le=200)]
+
+
+class SignalRequest(BaseModel):
+    query: SelectionQuery
+    rules: SignalRules = SignalRules()
+
+
+class SignalRun(BaseModel):
+    signal_id: str
+    result: SignalResult
+
+
+@router.post("", response_model=SignalRun, summary="生成一次交易信号（同步）并落库")
+def run_signal(
+    req: SignalRequest,
+    service: SignalServiceDep,
+    signal_repo: SignalRepoDep,
+    session: DbSession,
+) -> SignalRun:
+    result = service.signal(req.query, req.rules)
+    signal_id = new_id("SIG")
+    signal_repo.save(signal_id, result)
+    session.commit()
+    return SignalRun(signal_id=signal_id, result=result)
+
+
+@router.get("/{signal_id}", response_model=SignalResult, summary="读回一次信号结果")
+def get_signal(signal_id: str, signal_repo: SignalRepoDep) -> SignalResult:
+    result = signal_repo.get(signal_id)
+    if result is None:
+        raise HTTPException(status_code=404, detail=f"信号记录 {signal_id} 不存在")
+    return result
+
+
+@router.get("", response_model=list[SignalMeta], summary="历史信号元数据列表")
+def list_signals(
+    signal_repo: SignalRepoDep,
+    as_of: _AsOfQuery = None,
+    limit: _LimitQuery = 20,
+) -> list[SignalMeta]:
+    return signal_repo.list_recent(as_of=as_of, limit=limit)

backend/app/application/services/signal_service.py

@@ -0,0 +1,39 @@
+"""信号用例（M8.1）：基于选股评分排序 + 技术条件生成交易信号。
+
+信号与回测买入逻辑同源（同一评分引擎、同一口径），保证「为什么 BUY/SELL」可解释。
+"""
+
+from __future__ import annotations
+
+from datetime import date, timedelta
+
+import pandas as pd
+
+from app.domain.entities.selection import SelectionQuery
+from app.domain.entities.signal import SignalResult, SignalRules
+from app.domain.repositories.market import DailyBarRepository, StockRepository
+from app.quant.selection import factor_columns
+from app.quant.service import filter_stocks, load_daily_df
+from app.quant.signal import generate_signals
+
+
+class SignalService:
+    def __init__(self, stock_repo: StockRepository, daily_repo: DailyBarRepository) -> None:
+        self._stock_repo = stock_repo
+        self._daily_repo = daily_repo
+
+    def signal(self, query: SelectionQuery, rules: SignalRules) -> SignalResult:
+        as_of = query.as_of or date.today()
+        stocks = filter_stocks(self._stock_repo.list(), query.universe, as_of=as_of)
+        if not stocks:
+            return generate_signals(pd.DataFrame(), query, rules, as_of)
+        columns = sorted(factor_columns(query))
+        daily = load_daily_df(
+            self._daily_repo,
+            [s.symbol for s in stocks],
+            as_of - timedelta(days=query.warmup_days),
+            as_of,
+            columns,
+            adjust=query.price_adjustment,
+        )
+        return generate_signals(daily, query, rules, as_of)

backend/app/domain/entities/signal.py

@@ -0,0 +1,57 @@
+"""交易信号领域实体（M8.1，v2 §15 Signal Engine）。
+
+Signal 输入 = Selection 排序（score）+ 价格/技术条件 + 规则；输出事件可解释：
+BUY / WATCH / SELL（破位警示），每条带 trigger_reason —— 回答
+「某日为什么对该股票给 BUY/SELL」（v2 §8）。
+"""
+
+from __future__ import annotations
+
+from datetime import date, datetime
+
+from pydantic import BaseModel, Field
+
+
+class SignalRules(BaseModel):
+    """规则（结构化，MVP）：买入区间 + 趋势/动量条件 + 卖出/警示区间。"""
+
+    buy_rank_threshold: int = Field(default=20, ge=1, le=500, description="rank<=此值进入买入候选")
+    buy_require_trend: bool = Field(default=True, description="买入需 close > MA(trend_ma)")
+    buy_require_momentum: bool = Field(default=False, description="买入需 close > 20 日前 close")
+    trend_ma: int = Field(default=60, ge=10, le=250)
+    sell_rank_threshold: int = Field(default=50, ge=1, le=1000, description="rank>此值或破位 → SELL 警示")
+    sell_on_trend_break: bool = Field(default=True, description="买入区间内 close < MA(trend_ma) → SELL")
+    max_output_rank: int = Field(default=80, ge=1, le=2000, description="仅输出排名前 N 的信号")
+
+
+class SignalEvent(BaseModel):
+    symbol: str
+    signal_date: date
+    signal_type: str = Field(pattern="^(BUY|WATCH|SELL)$")
+    score: float | None = None
+    price: float | None = None
+    trigger_reason: list[str] = Field(default_factory=list)
+
+
+class SignalStatistics(BaseModel):
+    universe_size: int = 0
+    buy: int = 0
+    watch: int = 0
+    sell: int = 0
+
+
+class SignalResult(BaseModel):
+    as_of_date: date
+    rules: SignalRules
+    statistics: SignalStatistics
+    events: list[SignalEvent] = Field(default_factory=list)
+    config_snapshot: dict = Field(default_factory=dict)
+
+
+class SignalMeta(BaseModel):
+    id: str
+    as_of: date
+    buy: int = 0
+    watch: int = 0
+    sell: int = 0
+    created_at: datetime | None = None

backend/app/domain/repositories/signal.py

@@ -0,0 +1,19 @@
+"""Signal Repository Protocol（M8.1 落库）。"""
+
+from __future__ import annotations
+
+from datetime import date
+from typing import Protocol
+
+from app.domain.entities.signal import SignalMeta, SignalResult
+
+
+class SignalRepository(Protocol):
+    def save(self, signal_id: str, result: SignalResult) -> None:
+        """snapshot 一行 + 事件逐行（同事务，调用方 commit）。"""
+
+    def get(self, signal_id: str) -> SignalResult | None: ...
+
+    def list_recent(
+        self, as_of: date | None = None, limit: int = 20
+    ) -> list[SignalMeta]: ...

backend/app/infrastructure/persistence/migrations/versions/d8e0b2f3c4d5_signal_tables.py

@@ -0,0 +1,62 @@
+"""signal_snapshot / signal_event 表（M8.1 交易信号）
+
+Revision ID: d8e0b2f3c4d5
+Revises: c3e9a0d1f4b5
+Create Date: 2026-09-09
+
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "d8e0b2f3c4d5"
+down_revision: str | None = "c3e9a0d1f4b5"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "signal_snapshot",
+        sa.Column("id", sa.String(length=32), nullable=False),
+        sa.Column("as_of", sa.Date(), nullable=False),
+        sa.Column("query_json", sa.Text(), nullable=False),
+        sa.Column("rules_json", sa.Text(), nullable=False),
+        sa.Column("statistics_json", sa.Text(), nullable=False),
+        sa.Column("created_at", sa.DateTime(), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("ix_signal_snapshot_as_of", "signal_snapshot", ["as_of"])
+    op.create_index("ix_signal_snapshot_created_at", "signal_snapshot", ["created_at"])
+
+    op.create_table(
+        "signal_event",
+        sa.Column(
+            "id",
+            sa.BigInteger().with_variant(sa.Integer(), "sqlite"),
+            autoincrement=True,
+            nullable=False,
+        ),
+        sa.Column("signal_id", sa.String(length=32), nullable=False),
+        sa.Column("symbol", sa.String(length=12), nullable=False),
+        sa.Column("signal_date", sa.Date(), nullable=False),
+        sa.Column("signal_type", sa.String(length=8), nullable=False),
+        sa.Column("score", sa.Numeric(precision=14, scale=6), nullable=True),
+        sa.Column("price", sa.Numeric(precision=14, scale=4), nullable=True),
+        sa.Column("reason_json", sa.Text(), nullable=True),
+        sa.Column("created_at", sa.DateTime(), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("ix_signal_event_signal_id", "signal_event", ["signal_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_signal_event_signal_id", table_name="signal_event")
+    op.drop_table("signal_event")
+    op.drop_index("ix_signal_snapshot_created_at", table_name="signal_snapshot")
+    op.drop_index("ix_signal_snapshot_as_of", table_name="signal_snapshot")
+    op.drop_table("signal_snapshot")

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

@@ -26,3 +26,7 @@ from app.infrastructure.persistence.sqlalchemy.models.selection import (  # noqa
     SelectionResultModel,
     SelectionSnapshotModel,
 )
+from app.infrastructure.persistence.sqlalchemy.models.signal import (  # noqa: F401
+    SignalEventModel,
+    SignalSnapshotModel,
+)

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

@@ -0,0 +1,41 @@
+"""交易信号表（M8.1）。
+
+signal_snapshot：一次信号运行的查询/规则/统计快照
+signal_event：逐信号（signal_type + score/price + trigger_reason JSON）
+"""
+
+from __future__ import annotations
+
+from datetime import date, datetime
+
+from sqlalchemy import BigInteger, Date, DateTime, Integer, Numeric, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.infrastructure.persistence.sqlalchemy.base import Base
+
+PK_INT = BigInteger().with_variant(Integer, "sqlite")
+
+
+class SignalSnapshotModel(Base):
+    __tablename__ = "signal_snapshot"
+
+    id: Mapped[str] = mapped_column(String(32), primary_key=True)
+    as_of: Mapped[date] = mapped_column(Date, index=True)
+    query_json: Mapped[str] = mapped_column(Text)
+    rules_json: Mapped[str] = mapped_column(Text)
+    statistics_json: Mapped[str] = mapped_column(Text)
+    created_at: Mapped[datetime] = mapped_column(DateTime, index=True)
+
+
+class SignalEventModel(Base):
+    __tablename__ = "signal_event"
+
+    id: Mapped[int] = mapped_column(PK_INT, primary_key=True, autoincrement=True)
+    signal_id: Mapped[str] = mapped_column(String(32), index=True)
+    symbol: Mapped[str] = mapped_column(String(12))
+    signal_date: Mapped[date] = mapped_column(Date)
+    signal_type: Mapped[str] = mapped_column(String(8))
+    score: Mapped[float | None] = mapped_column(Numeric(14, 6), nullable=True)
+    price: Mapped[float | None] = mapped_column(Numeric(14, 4), nullable=True)
+    reason_json: Mapped[str | None] = mapped_column(Text, nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime)

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

@@ -0,0 +1,108 @@
+"""Signal Repository 的 SQLAlchemy 实现（M8.1）。"""
+
+from __future__ import annotations
+
+import json
+from datetime import date, datetime
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
+from app.domain.entities.signal import (
+    SignalEvent,
+    SignalMeta,
+    SignalResult,
+    SignalRules,
+    SignalStatistics,
+)
+from app.infrastructure.persistence.sqlalchemy.models.signal import (
+    SignalEventModel,
+    SignalSnapshotModel,
+)
+
+
+class SqlAlchemySignalRepository:
+    def __init__(self, session: Session) -> None:
+        self._session = session
+
+    def save(self, signal_id: str, result: SignalResult) -> None:
+        self._session.add(
+            SignalSnapshotModel(
+                id=signal_id,
+                as_of=result.as_of_date,
+                query_json=json.dumps(
+                    {
+                        "as_of": result.as_of_date.isoformat(),
+                        **{k: v for k, v in result.config_snapshot.items() if k != "as_of"},
+                    },
+                    ensure_ascii=False,
+                ),
+                rules_json=json.dumps(result.rules.model_dump(mode="json"), ensure_ascii=False),
+                statistics_json=json.dumps(result.statistics.model_dump(mode="json")),
+                created_at=datetime.now(),
+            )
+        )
+        now = datetime.now()
+        for e in result.events:
+            self._session.add(
+                SignalEventModel(
+                    signal_id=signal_id,
+                    symbol=e.symbol,
+                    signal_date=e.signal_date,
+                    signal_type=e.signal_type,
+                    score=e.score,
+                    price=e.price,
+                    reason_json=json.dumps(e.trigger_reason, ensure_ascii=False),
+                    created_at=now,
+                )
+            )
+        self._session.flush()
+
+    def get(self, signal_id: str) -> SignalResult | None:
+        snap = self._session.get(SignalSnapshotModel, signal_id)
+        if snap is None:
+            return None
+        rows = self._session.scalars(
+            select(SignalEventModel)
+            .where(SignalEventModel.signal_id == signal_id)
+            .order_by(SignalEventModel.signal_type, SignalEventModel.symbol)
+        ).all()
+        rules = SignalRules.model_validate_json(snap.rules_json)
+        stats = SignalStatistics.model_validate_json(snap.statistics_json)
+        return SignalResult(
+            as_of_date=snap.as_of,
+            rules=rules,
+            statistics=stats,
+            events=[
+                SignalEvent(
+                    symbol=r.symbol,
+                    signal_date=r.signal_date,
+                    signal_type=r.signal_type,
+                    score=float(r.score) if r.score is not None else None,
+                    price=float(r.price) if r.price is not None else None,
+                    trigger_reason=json.loads(r.reason_json or "[]"),
+                )
+                for r in rows
+            ],
+            config_snapshot={"as_of": snap.as_of.isoformat()},
+        )
+
+    def list_recent(self, as_of: date | None = None, limit: int = 20) -> list[SignalMeta]:
+        stmt = select(SignalSnapshotModel).order_by(SignalSnapshotModel.created_at.desc())
+        if as_of is not None:
+            stmt = stmt.where(SignalSnapshotModel.as_of == as_of)
+        stmt = stmt.limit(limit)
+        metas: list[SignalMeta] = []
+        for snap in self._session.scalars(stmt).all():
+            stats = SignalStatistics.model_validate_json(snap.statistics_json)
+            metas.append(
+                SignalMeta(
+                    id=snap.id,
+                    as_of=snap.as_of,
+                    buy=stats.buy,
+                    watch=stats.watch,
+                    sell=stats.sell,
+                    created_at=snap.created_at,
+                )
+            )
+        return metas

backend/app/quant/signal.py

@@ -0,0 +1,135 @@
+"""Signal Engine（v2 §15）—— 纯 pandas 执行。
+
+输入：行情长表（<=as_of）+ SelectionQuery（评分因子）+ SignalRules。
+流程：复合分 → 全市场 rank → 按规则判定 BUY / WATCH / SELL，
+事件带 trigger_reason 与 score/price（可解释）。回测的买入逻辑（TopK+可买过滤）
+与这里的 BUY 建议同源于同一评分引擎（v2 §25 一致）。
+"""
+
+from __future__ import annotations
+
+from datetime import date
+
+import pandas as pd
+
+from app.domain.entities.selection import SelectionQuery
+from app.domain.entities.signal import (
+    SignalEvent,
+    SignalResult,
+    SignalRules,
+    SignalStatistics,
+)
+from app.quant.composite import build_score_panel
+from app.quant.selection import resolve_observation_date
+
+
+def generate_signals(
+    daily: pd.DataFrame,
+    query: SelectionQuery,
+    rules: SignalRules,
+    as_of: date | None,
+) -> SignalResult:
+    if not query.factors:
+        raise ValueError("signal 需要评分因子（SelectionQuery.factors）")
+    obs = resolve_observation_date(daily, as_of)
+    resolved = (obs.date() if obs is not None else as_of) or date.today()
+    if obs is None or daily.empty:
+        return _empty(query, rules, resolved)
+    view = daily[pd.to_datetime(daily["trade_date"]) <= obs]
+
+    score = build_score_panel(view, query.factors).loc[obs].dropna().sort_values(ascending=False)
+    close = view.pivot(index="trade_date", columns="symbol", values="close").sort_index()
+    close.index = pd.to_datetime(close.index)
+    c_d = close.loc[obs]
+    ma_d = close.rolling(rules.trend_ma).mean().loc[obs]
+    mom20_d = (close / close.shift(20) - 1.0).loc[obs]
+
+    events: list[SignalEvent] = []
+    stats = SignalStatistics(universe_size=int(len(score)))
+    for rank, (sym, sc) in enumerate(score.items(), start=1):
+        if rank > rules.max_output_rank:
+            break
+        c = _num(c_d.get(sym))
+        ma = _num(ma_d.get(sym))
+        mom = _num(mom20_d.get(sym))
+        price = float(c) if c is not None else None
+        reason: list[str] = []
+        event_type = "WATCH"
+
+        trend_ok = c is not None and ma is not None and c > ma
+        momentum_ok = mom is not None and mom > 0
+        if rank <= rules.buy_rank_threshold and (
+            not rules.buy_require_trend or trend_ok
+        ) and (not rules.buy_require_momentum or momentum_ok):
+            event_type = "BUY"
+            reason = [f"综合分排名第 {rank}（≤买入阈值 {rules.buy_rank_threshold}）"]
+            if rules.buy_require_trend:
+                reason.append(f"close > MA{rules.trend_ma}（趋势向上）")
+            if rules.buy_require_momentum:
+                reason.append("close > 20 日前收盘（动量为正）")
+        elif rank <= rules.buy_rank_threshold:
+            event_type = "WATCH"
+            reason = [f"综合分排名第 {rank}（买入区间）"]
+            if rules.buy_require_trend and not trend_ok:
+                reason.append(f"但 close < MA{rules.trend_ma}（趋势未确认）")
+        elif rank <= rules.sell_rank_threshold:
+            # 观望带
+            if rules.sell_on_trend_break and c is not None and ma is not None and c < ma:
+                event_type = "SELL"
+                reason = [f"跌破 MA{rules.trend_ma}（持仓者应卖出/减仓），rank={rank}"]
+            else:
+                event_type = "WATCH"
+                reason = [f"rank={rank}（买入区间外、卖出区间内：观望）"]
+        else:
+            event_type = "SELL"
+            reason = [f"综合分排名第 {rank}（>卖出阈值 {rules.sell_rank_threshold}，持仓者应卖出）"]
+        if c is not None and c < 0:
+            continue  # 防御负价
+        events.append(
+            SignalEvent(
+                symbol=sym,
+                signal_date=resolved,
+                signal_type=event_type,
+                score=round(float(sc), 6),
+                price=round(price, 4) if price is not None else None,
+                trigger_reason=reason,
+            )
+        )
+        if event_type == "BUY":
+            stats.buy += 1
+        elif event_type == "SELL":
+            stats.sell += 1
+        else:
+            stats.watch += 1
+
+    return SignalResult(
+        as_of_date=resolved,
+        rules=rules,
+        statistics=stats,
+        events=events,
+        config_snapshot={
+            "as_of": resolved.isoformat(),
+            "factors": [f.model_dump() for f in query.factors],
+            "rules": rules.model_dump(mode="json"),
+        },
+    )
+
+
+def _num(v) -> float | None:
+    if v is None:
+        return None
+    try:
+        f = float(v)
+    except (TypeError, ValueError):
+        return None
+    return None if f != f else f  # NaN → None
+
+
+def _empty(query: SelectionQuery, rules: SignalRules, resolved: date) -> SignalResult:
+    return SignalResult(
+        as_of_date=resolved,
+        rules=rules,
+        statistics=SignalStatistics(),
+        events=[],
+        config_snapshot={"as_of": resolved.isoformat(), "rules": rules.model_dump(mode="json")},
+    )