fix: preserve legacy monitoring migration data

backend/app/models/device.py

@@ -36,6 +36,23 @@ class DeviceMonitoringPolicy:
     degraded_loss_percent: float
     recovery_consecutive_clean_rounds: int
 
+    @staticmethod
+    def _resolve_override(
+        override: object,
+        default: int | float,
+        minimum: int | float,
+        maximum: int | float,
+    ) -> int | float:
+        """Use a bounded persisted override or retain the validated default."""
+        if (
+            isinstance(override, bool)
+            or not isinstance(override, (int, float))
+            or override < minimum
+            or override > maximum
+        ):
+            return default
+        return override
+
     @classmethod
     def from_device(
         cls,
@@ -45,29 +62,44 @@ class DeviceMonitoringPolicy:
         """Resolve device overrides without changing the stored device."""
         return cls(
             probe_packets_per_round=(
-                device.probe_packets_per_round
-                if device.probe_packets_per_round is not None
-                else settings.probe_packets_per_round
+                cls._resolve_override(
+                    device.probe_packets_per_round,
+                    settings.probe_packets_per_round,
+                    1,
+                    10,
+                )
             ),
             offline_consecutive_rounds=(
-                device.offline_consecutive_rounds
-                if device.offline_consecutive_rounds is not None
-                else settings.offline_consecutive_rounds
+                cls._resolve_override(
+                    device.offline_consecutive_rounds,
+                    settings.offline_consecutive_rounds,
+                    1,
+                    10,
+                )
             ),
             degraded_window_rounds=(
-                device.degraded_window_rounds
-                if device.degraded_window_rounds is not None
-                else settings.degraded_window_rounds
+                cls._resolve_override(
+                    device.degraded_window_rounds,
+                    settings.degraded_window_rounds,
+                    2,
+                    60,
+                )
             ),
             degraded_loss_percent=(
-                device.degraded_loss_percent
-                if device.degraded_loss_percent is not None
-                else settings.degraded_loss_percent
+                cls._resolve_override(
+                    device.degraded_loss_percent,
+                    settings.degraded_loss_percent,
+                    1,
+                    100,
+                )
             ),
             recovery_consecutive_clean_rounds=(
-                device.recovery_consecutive_clean_rounds
-                if device.recovery_consecutive_clean_rounds is not None
-                else settings.recovery_consecutive_clean_rounds
+                cls._resolve_override(
+                    device.recovery_consecutive_clean_rounds,
+                    settings.recovery_consecutive_clean_rounds,
+                    1,
+                    20,
+                )
             ),
         )