fix(P0): 修复三处静默失效的阻断缺陷

P0-1 backtest 会话生命周期:
- _get_historical_matches 加 selectinload(league/home_team/away_team),
  并在 session 内物化为 BacktestCandidate 纯数据快照,避免 session
  关闭后访问惰性关系抛 MissingGreenlet
- except 收窄并改用 logger.exception 保留堆栈
- 移除未使用的 and_ / League 导入

P0-2 切片函数关系属性 MissingGreenlet:
- models.py 为 Match.league/home_team/away_team/stats 声明 lazy=selectin
- context_builder 的 _get_form/_get_h2h/_get_home_away 显式 selectinload
  (修复 form_slice/h2h_slice 恒定失败,被 fail-open 掩盖的问题)
- repositories.find_by_teams_and_date 加 selectinload(Match.stats)

P0-3 bzzoiro raw 变量泄漏导致血缘错乱:
- normalized_matches 改为携带 (nm, raw) 元组,内层循环解包
- source_event_id / source_record_id 现在取到正确 event id
- 已有比赛补建 stats 时补齐 source/source_event_id/retrieved_at/available_at
- 抽取 _match_key()/_to_date() 统一日期键构造 (P1-6)

src/llm/predict.py

@@ -81,11 +81,22 @@ async def predict_match(
     model: str | None = None,
     prompt_version: str | None = None,
     mode: str = "multi",
+    use_cache: bool = True,
 ) -> "PredictResult | MultiPredictResult":
-    """预测入口。mode=multi(默认)走多 agent;mode=single 走单次调用。"""
+    """预测入口。mode=multi(默认)走多 agent;mode=single 走单次调用。
+
+    Args:
+        use_cache: 是否允许返回进程内缓存结果。回测必须传 False——
+            缓存命中不会新建 prediction 行,调用方会对同一个 prediction_id
+            反复 settle,把不同比赛的真实比分覆盖到同一条记录上。
+    """
     if mode == "single":
         return await _predict_single(
-            match_id, provider=provider, model=model, prompt_version=prompt_version
+            match_id,
+            provider=provider,
+            model=model,
+            prompt_version=prompt_version,
+            use_cache=use_cache,
         )
     from src.llm.agents.orchestrator import predict_match_multi
 
@@ -98,6 +109,7 @@ async def _predict_single(
     provider: LLMProvider | None = None,
     model: str | None = None,
     prompt_version: str | None = None,
+    use_cache: bool = True,
 ) -> PredictResult:
     """单次调用路径(原有实现)。"""
     if provider is None:
@@ -107,10 +119,11 @@ async def _predict_single(
     version = prompt_version or "v1"
 
     # 0. 查缓存(同 match+provider+model+version 5 分钟内直接返)
-    cached = _get_cached(match_id, settings.LLM_PROVIDER, provider.model, version)
-    if cached is not None:
-        logger.debug("predict cache hit match=%s", match_id)
-        return cached
+    if use_cache:
+        cached = _get_cached(match_id, settings.LLM_PROVIDER, provider.model, version)
+        if cached is not None:
+            logger.debug("predict cache hit match=%s", match_id)
+            return cached
 
     # 1. 拼上下文
     ctx = await build_context(match_id)
@@ -191,6 +204,7 @@ async def _predict_single(
             raw=resp.raw,
         )
 
-        # 5. 写入缓存
-        _set_cached(match_id, settings.LLM_PROVIDER, provider.model, version, result)
+        # 5. 写入缓存(仅当允许缓存时)
+        if use_cache:
+            _set_cached(match_id, settings.LLM_PROVIDER, provider.model, version, result)
         return result