feat(devices): auto-resolve active alerts when monitoring is disabled

When a user flips monitoring_enabled true → false on a device, any
unresolved alerts on that device are now resolved silently — the
operator has deliberately stopped monitoring it, so leaving stale
"device down" pages around is noise.

- Alerts.resolve_active_alerts_for_device/1: bulk-resolves via
  resolve_alert_silent so PagerDuty/email don't fire
- Devices.handle_monitoring_changes hooks it on the disable transition

lib/towerops/alerts.ex

@@ -370,6 +370,23 @@ defmodule Towerops.Alerts do
     do_acknowledge_alert(alert, nil)
   end
 
+  @doc """
+  Resolves every active (unresolved) alert for the given device.
+
+  Used when the user takes a deliberate action that makes the alerts
+  meaningless — e.g. disabling monitoring on a device. Resolves silently
+  so downstream notification channels (PagerDuty, email) don't fire a
+  spurious "resolved" event.
+  """
+  def resolve_active_alerts_for_device(device_id) do
+    from(a in Alert,
+      where: a.device_id == ^device_id,
+      where: is_nil(a.resolved_at)
+    )
+    |> Repo.all()
+    |> Enum.each(&resolve_alert_silent/1)
+  end
+
   # Performs the database update for resolving an alert
   defp do_resolve_alert(alert) do
     alert

lib/towerops/devices.ex

@@ -6,6 +6,7 @@ defmodule Towerops.Devices do
   import Ecto.Query
 
   alias Towerops.Agents
+  alias Towerops.Alerts
   alias Towerops.Devices.CredentialResolver
   alias Towerops.Devices.Device, as: DeviceSchema
   alias Towerops.Devices.DeviceQuery
@@ -982,6 +983,10 @@ defmodule Towerops.Devices do
 
       !device.monitoring_enabled && old_monitoring ->
         _ = DeviceMonitorWorker.stop_monitoring(device.id)
+        # Active alerts on this device are no longer meaningful — the user
+        # has deliberately stopped monitoring it. Resolve silently so we
+        # don't page anyone about the resolution.
+        _ = Alerts.resolve_active_alerts_for_device(device.id)
 
       true ->
         :ok

test/towerops/devices_test.exs

@@ -2,6 +2,7 @@ defmodule Towerops.EquipmentTest do
   use Towerops.DataCase
   use ExUnitProperties
 
+  alias Towerops.Alerts.Alert
   alias Towerops.Devices
   alias Towerops.Devices.Device
 
@@ -131,6 +132,54 @@ defmodule Towerops.EquipmentTest do
       assert device.monitoring_enabled == false
     end
 
+    test "update_device/2 disabling monitoring auto-resolves active alerts on the device",
+         %{organization: organization, site: site} do
+      {:ok, device} =
+        Devices.create_device(Map.merge(@valid_attrs, %{site_id: site.id, organization_id: organization.id}))
+
+      {:ok, alert} =
+        Towerops.Alerts.create_alert(%{
+          device_id: device.id,
+          organization_id: organization.id,
+          alert_type: "device_down",
+          severity: 2,
+          message: "Device unreachable",
+          triggered_at: DateTime.utc_now()
+        })
+
+      assert is_nil(alert.resolved_at)
+
+      assert {:ok, updated} =
+               Devices.update_device(device, %{monitoring_enabled: false})
+
+      assert updated.monitoring_enabled == false
+
+      reloaded_alert = Towerops.Repo.get!(Alert, alert.id)
+      assert reloaded_alert.resolved_at, "alert should be auto-resolved"
+    end
+
+    test "update_device/2 leaves alerts alone when monitoring stays enabled",
+         %{organization: organization, site: site} do
+      {:ok, device} =
+        Devices.create_device(Map.merge(@valid_attrs, %{site_id: site.id, organization_id: organization.id}))
+
+      {:ok, alert} =
+        Towerops.Alerts.create_alert(%{
+          device_id: device.id,
+          organization_id: organization.id,
+          alert_type: "device_down",
+          severity: 2,
+          message: "Device unreachable",
+          triggered_at: DateTime.utc_now()
+        })
+
+      # Updating something unrelated should not touch alerts
+      assert {:ok, _updated} = Devices.update_device(device, %{name: "Renamed"})
+
+      reloaded_alert = Towerops.Repo.get!(Alert, alert.id)
+      assert is_nil(reloaded_alert.resolved_at)
+    end
+
     test "update_device/2 with invalid data returns error changeset", %{organization: organization, site: site} do
       {:ok, device} =
         Devices.create_device(Map.merge(@valid_attrs, %{site_id: site.id, organization_id: organization.id}))