fix: Preserve ackState for old acknowledged alerts during restore

When LoadActiveAlerts skipped acknowledged alerts older than 1 hour,
it was also not populating ackState. This meant that when the same
alert (e.g., backup-age) was recreated on the next poll cycle,
preserveAlertState couldn't find any acknowledgement record and
the alert would retrigger notifications.

Now ackState is populated even for skipped old acknowledged alerts,
so if they reappear, the acknowledgement will be restored.

Related to #1043

internal/alerts/alerts.go

@@ -8726,9 +8726,20 @@ func (m *Manager) LoadActiveAlerts() error {
 			continue
 		}
 
-		// Skip acknowledged alerts older than 1 hour
+		// Skip acknowledged alerts older than 1 hour from activeAlerts,
+		// but still preserve the ackState so if the same alert reappears
+		// (e.g., backup-age alerts) it won't retrigger notifications.
 		if alert.Acknowledged && alert.AckTime != nil && now.Sub(*alert.AckTime) > time.Hour {
-			log.Debug().Str("alertID", alert.ID).Msg("Skipping old acknowledged alert")
+			log.Debug().Str("alertID", alert.ID).Msg("Skipping old acknowledged alert from activeAlerts but preserving ackState")
+			ackTime := alert.StartTime
+			if alert.AckTime != nil {
+				ackTime = *alert.AckTime
+			}
+			m.ackState[alert.ID] = ackRecord{
+				acknowledged: true,
+				user:         alert.AckUser,
+				time:         ackTime,
+			}
 			continue
 		}
 

internal/alerts/alerts_test.go

@@ -15343,10 +15343,22 @@ func TestLoadActiveAlerts(t *testing.T) {
 
 		m.mu.RLock()
 		_, exists := m.activeAlerts["old-ack-alert"]
+		ackRecord, ackExists := m.ackState["old-ack-alert"]
 		m.mu.RUnlock()
 
 		if exists {
-			t.Error("old acknowledged alert (>1h) should be skipped during load")
+			t.Error("old acknowledged alert (>1h) should be skipped from activeAlerts")
+		}
+
+		// But ackState should be preserved so the alert doesn't retrigger if it reappears
+		if !ackExists {
+			t.Error("ackState should be preserved for old acknowledged alerts to prevent retriggering")
+		}
+		if ackExists && !ackRecord.acknowledged {
+			t.Error("ackState.acknowledged should be true")
+		}
+		if ackExists && ackRecord.user != "testuser" {
+			t.Errorf("ackState.user should be 'testuser', got %q", ackRecord.user)
 		}
 	})