docs: record reproducible risk artifact contract

README.md

@@ -139,6 +139,16 @@ print(factor_backtest.benchmark_stats(benchmark_returns))
 
 # 下游稳定交付：显式提供代码版本、数据快照和时区，不在核心层写数据库。
 from quant_engine.artifact import build_research_run_artifact
+from quant_engine.risk import CovarianceSnapshot
+
+risk_date = factor_backtest.position_weights.index[-1].date()
+risk_snapshot = CovarianceSnapshot(
+    snapshot_id="<covariance-snapshot-id>",
+    as_of_date=risk_date,
+    covariance=daily_return_covariance,
+    return_frequency="1d",
+    periods_per_year=252,
+)
 
 artifact = build_research_run_artifact(
     factor_backtest,
@@ -156,6 +166,7 @@ artifact = build_research_run_artifact(
     parameters={"top_k": 20, "lag_sessions": 1},
     benchmark_id="000300.SH",
     benchmark_returns=benchmark_returns,
+    risk_snapshots={risk_date: risk_snapshot},
 )
 print(artifact.manifest())