feat(CORE-001D3B): surface alert history degraded state

app/services/alerts.py

@@ -2,15 +2,18 @@
 
 from __future__ import annotations
 
+import logging
 from dataclasses import dataclass
 from decimal import Decimal
 from typing import Mapping
 
 from app.domain.portfolio_math import build_alert_context
-from app.models.alerts import AlertEvent, AlertHistoryRepository, AlertStatus
+from app.models.alerts import AlertEvent, AlertHistoryLoadError, AlertHistoryRepository, AlertStatus
 from app.models.portfolio import PortfolioConfig
 from app.services.boundary_values import boundary_decimal
 
+logger = logging.getLogger(__name__)
+
 
 @dataclass(frozen=True, slots=True)
 class AlertEvaluationInput:
@@ -74,7 +77,18 @@ class AlertService:
     def evaluate(
         self, config: PortfolioConfig, portfolio: Mapping[str, object], *, persist: bool = True
     ) -> AlertStatus:
-        history = self.repository.load() if persist else []
+        history: list[AlertEvent] = []
+        history_unavailable = False
+        history_notice: str | None = None
+        try:
+            history = self.repository.load()
+        except AlertHistoryLoadError as exc:
+            history_unavailable = True
+            history_notice = (
+                "Alert history is temporarily unavailable due to a storage error. New alerts are not being recorded."
+            )
+            logger.warning("Alert history unavailable at %s: %s", exc.history_path, exc)
+
         evaluation = _normalize_alert_evaluation_input(config, portfolio)
 
         if evaluation.ltv_ratio >= evaluation.critical_threshold:
@@ -106,12 +120,21 @@ class AlertService:
                 email_alerts_enabled=evaluation.email_alerts_enabled,
             )
             if persist:
-                if self._should_record(history, event):
+                if not history_unavailable and self._should_record(history, event):
                     history.append(event)
                     self.repository.save(history)
             else:
                 preview_history = [event]
 
+        if not persist:
+            resolved_history = preview_history
+        elif history_unavailable:
+            resolved_history = []
+        elif severity != "ok":
+            resolved_history = list(reversed(self.repository.load()))
+        else:
+            resolved_history = history
+
         return AlertStatus(
             severity=severity,
             message=message,
@@ -119,11 +142,9 @@ class AlertService:
             warning_threshold=float(evaluation.warning_threshold),
             critical_threshold=float(evaluation.critical_threshold),
             email_alerts_enabled=evaluation.email_alerts_enabled,
-            history=(
-                preview_history
-                if not persist
-                else list(reversed(self.repository.load() if severity != "ok" else history))
-            ),
+            history=resolved_history,
+            history_unavailable=history_unavailable,
+            history_notice=history_notice,
         )
 
     @staticmethod