fix(CORE-001D3B): reject malformed alert history entries

app/models/alerts.py

@@ -67,7 +67,18 @@ class AlertHistoryRepository:
             raise AlertHistoryLoadError(self.history_path, f"Alert history could not be read: {exc}") from exc
         if not isinstance(data, list):
             raise AlertHistoryLoadError(self.history_path, "Alert history payload must be a list")
-        return [AlertEvent.from_dict(item) for item in data if isinstance(item, dict)]
+        events: list[AlertEvent] = []
+        for index, item in enumerate(data):
+            if not isinstance(item, dict):
+                raise AlertHistoryLoadError(self.history_path, f"Alert history entry {index} must be an object")
+            try:
+                events.append(AlertEvent.from_dict(item))
+            except (TypeError, ValueError) as exc:
+                raise AlertHistoryLoadError(
+                    self.history_path,
+                    f"Alert history entry {index} is invalid: {exc}",
+                ) from exc
+        return events
 
     def save(self, events: list[AlertEvent]) -> None:
         with self.history_path.open("w") as f: