rebuild(stage-5): establish market data gateway and charts

next/backend/data/quality.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+from backend.data.contracts import ProviderResult
+
+
+class DataQualityError(RuntimeError):
+    pass
+
+
+MINIMUM_COVERAGE = {
+    "calendar": 1.0,
+    "entities": 0.98,
+    "daily_chart": 1.0,
+    "minute_chart": 1.0,
+}
+
+
+def require_quality(dataset: str, result: ProviderResult) -> ProviderResult:
+    minimum = MINIMUM_COVERAGE.get(dataset, 1.0)
+    if not result.rows:
+        raise DataQualityError(f"{dataset} returned no real observations")
+    if result.metadata.coverage < minimum:
+        raise DataQualityError(
+            f"{dataset} coverage {result.metadata.coverage:.3f} is below {minimum:.3f}"
+        )
+    return result