feat(monitoring): alert when backhaul radios lose connected clients

Backhaul radios (ePMP, AirOS, PMP, Cambium, MikroTik, RouterOS) now
monitor their connected client count with a low threshold of 1. When
the count drops to 0 the SnmpSensorExecutor marks it CRITICAL, which
triggers an alert through the existing check → alert pipeline.

- Adds  field to sensor_def type in Vendor behaviour
- Sets  on all clients-type wireless sensors in
  backhaul-capable vendor profiles
- Adds default executor handling: any clients sensor at 0 → status 2
- 3 new tests for clients sensor behavior

.gitignore

@@ -93,6 +93,7 @@ profiles.json
 .claude/
 .beads/
 .agents/
+.omo/
 .logs/
 .direnv/
 

lib/towerops/monitoring/executors/snmp_sensor_executor.ex

@@ -113,6 +113,9 @@ defmodule Towerops.Monitoring.Executors.SnmpSensorExecutor do
 
   defp determine_status(value, sensor) do
     cond do
+      # For "clients" type sensors, 0 connected clients means the link is down.
+      # This acts as default threshold when no explicit limits are configured.
+      sensor.sensor_type == "clients" and value == 0 -> 2
       critical_high?(value, sensor) -> 2
       critical_low?(value, sensor) -> 2
       warning_high?(value, sensor) -> 1

lib/towerops/snmp/profiles/vendors/airos.ex

@@ -161,13 +161,16 @@ defmodule Towerops.Snmp.Profiles.Vendors.Airos do
         sensor_unit: "Mbps",
         sensor_divisor: 1
       },
-      # ubntWlStatStaCount - entry 15
+      # ubntWlStatStaCount - entry 15 (station/client count)
+      # When client count drops to 0, the link to the far end is likely down.
+      # limit_low: 1 ensures this check becomes CRITICAL at 0 clients.
       %{
         oid: "1.3.6.1.4.1.41112.1.4.5.1.15.1",
         sensor_type: "clients",
         sensor_descr: "Clients",
         sensor_unit: "",
-        sensor_divisor: 1
+        sensor_divisor: 1,
+        metadata: %{"limit_low" => 1}
       },
 
       # === AirMax table (ubntAirMaxTable) - 1.3.6.1.4.1.41112.1.4.6 ===

lib/towerops/snmp/profiles/vendors/cambium.ex

@@ -124,7 +124,8 @@ defmodule Towerops.Snmp.Profiles.Vendors.Cambium do
               sensor_descr: "Connected Subscribers",
               sensor_unit: "",
               sensor_divisor: 1,
-              sensor_index: "cambium_epmp_clients"
+              sensor_index: "cambium_epmp_clients",
+              metadata: %{"limit_low" => 1}
             }
           ]
       else

lib/towerops/snmp/profiles/vendors/epmp.ex

@@ -124,12 +124,15 @@ defmodule Towerops.Snmp.Profiles.Vendors.Epmp do
         sensor_divisor: 1
       },
       # Connected clients count (AP only)
+      # When client count drops to 0, the link to the far end is likely down.
+      # limit_low: 1 ensures this check becomes CRITICAL at 0 clients.
       %{
         oid: "1.3.6.1.4.1.17713.21.1.2.10.0",
         sensor_type: "clients",
         sensor_descr: "Connected Clients",
         sensor_unit: "",
-        sensor_divisor: 1
+        sensor_divisor: 1,
+        metadata: %{"limit_low" => 1}
       },
       # === GPS sensors (from pollOS) ===
       # GPS Tracked Satellites

lib/towerops/snmp/profiles/vendors/mikrotik.ex

@@ -109,7 +109,8 @@ defmodule Towerops.Snmp.Profiles.Vendors.Mikrotik do
               sensor_unit: "",
               sensor_divisor: 1,
               sensor_index: "mikrotik_clients_#{index}",
-              last_value: client_count
+              last_value: client_count,
+              metadata: %{"limit_low" => 1}
             }
           ]
 

lib/towerops/snmp/profiles/vendors/pmp.ex

@@ -122,12 +122,14 @@ defmodule Towerops.Snmp.Profiles.Vendors.Pmp do
         sensor_divisor: 1000
       },
       # Client count (AP only)
+      # When client count drops to 0, the link to the far end is likely down.
       %{
         oid: "1.3.6.1.4.1.161.19.3.1.7.1.0",
         sensor_type: "clients",
         sensor_descr: "Registered SMs",
         sensor_unit: "",
-        sensor_divisor: 1
+        sensor_divisor: 1,
+        metadata: %{"limit_low" => 1}
       },
       # 1m Downlink Utilization
       %{

lib/towerops/snmp/profiles/vendors/routeros.ex

@@ -223,7 +223,8 @@ defmodule Towerops.Snmp.Profiles.Vendors.Routeros do
             sensor_descr: "#{prefix} Clients",
             sensor_unit: "",
             sensor_divisor: 1,
-            last_value: client_count / 1
+            last_value: client_count / 1,
+            metadata: %{"limit_low" => 1}
           }
           | sensors
         ]

lib/towerops/snmp/profiles/vendors/vendor.ex

@@ -15,15 +15,17 @@ defmodule Towerops.Snmp.Profiles.Vendors.Vendor do
           sensor_descr: String.t(),
           sensor_unit: String.t(),
           sensor_divisor: integer(),
-          last_value: float() | nil
+          last_value: float() | nil,
+          metadata: map()
         }
 
   @type sensor_def :: %{
-          oid: String.t(),
-          sensor_type: String.t(),
-          sensor_descr: String.t(),
-          sensor_unit: String.t(),
-          sensor_divisor: integer()
+          :oid => String.t(),
+          :sensor_type => String.t(),
+          :sensor_descr => String.t(),
+          :sensor_unit => String.t(),
+          :sensor_divisor => integer(),
+          optional(:metadata) => map()
         }
 
   @doc """
@@ -78,7 +80,8 @@ defmodule Towerops.Snmp.Profiles.Vendors.Vendor do
           sensor_descr: sensor_def.sensor_descr,
           sensor_unit: sensor_def.sensor_unit,
           sensor_divisor: sensor_def.sensor_divisor,
-          last_value: value / 1
+          last_value: value / 1,
+          metadata: Map.get(sensor_def, :metadata, %{})
         }
 
       _ ->

test/towerops/monitoring/executors/snmp_sensor_executor_test.exs

@@ -212,6 +212,134 @@ defmodule Towerops.Monitoring.Executors.SnmpSensorExecutorTest do
       assert error_msg =~ "Sensor not found"
     end
 
+    test "returns CRITICAL for clients sensor with 0 connected clients", %{
+      device: device,
+      snmp_device: snmp_device
+    } do
+      sensor =
+        %Sensor{}
+        |> Sensor.changeset(%{
+          snmp_device_id: snmp_device.id,
+          sensor_descr: "Connected Clients",
+          sensor_type: "clients",
+          sensor_index: "1",
+          sensor_oid: ".1.2.3.4",
+          sensor_unit: "",
+          sensor_divisor: 1
+        })
+        |> Repo.insert!()
+
+      {:ok, check} =
+        Monitoring.create_check(%{
+          organization_id: device.organization_id,
+          device_id: device.id,
+          name: "Connected Clients",
+          check_type: "snmp_sensor",
+          source_type: "auto_discovery",
+          source_id: sensor.id,
+          config: %{
+            "sensor_type" => "clients",
+            "sensor_oid" => ".1.2.3.4",
+            "sensor_unit" => ""
+          }
+        })
+
+      expect(SnmpMock, :get, fn _ip, _oid, _opts ->
+        {:ok, {:integer, 0}}
+      end)
+
+      assert {:ok, response} = SnmpSensorExecutor.execute(check)
+      assert response.value == 0.0
+      assert response.status == 2
+      assert response.output =~ "Connected Clients"
+      assert response.output =~ "0"
+    end
+
+    test "returns OK for clients sensor with connected clients > 0", %{
+      device: device,
+      snmp_device: snmp_device
+    } do
+      sensor =
+        %Sensor{}
+        |> Sensor.changeset(%{
+          snmp_device_id: snmp_device.id,
+          sensor_descr: "Connected Clients",
+          sensor_type: "clients",
+          sensor_index: "1",
+          sensor_oid: ".1.2.3.4",
+          sensor_unit: "",
+          sensor_divisor: 1
+        })
+        |> Repo.insert!()
+
+      {:ok, check} =
+        Monitoring.create_check(%{
+          organization_id: device.organization_id,
+          device_id: device.id,
+          name: "Connected Clients",
+          check_type: "snmp_sensor",
+          source_type: "auto_discovery",
+          source_id: sensor.id,
+          config: %{
+            "sensor_type" => "clients",
+            "sensor_oid" => ".1.2.3.4",
+            "sensor_unit" => ""
+          }
+        })
+
+      expect(SnmpMock, :get, fn _ip, _oid, _opts ->
+        {:ok, {:integer, 3}}
+      end)
+
+      assert {:ok, response} = SnmpSensorExecutor.execute(check)
+      assert response.value == 3.0
+      assert response.status == 0
+    end
+
+    test "returns OK for clients sensor with 0 when explicit limit_low > 0", %{
+      device: device,
+      snmp_device: snmp_device
+    } do
+      sensor =
+        %Sensor{}
+        |> Sensor.changeset(%{
+          snmp_device_id: snmp_device.id,
+          sensor_descr: "Connected Clients",
+          sensor_type: "clients",
+          sensor_index: "1",
+          sensor_oid: ".1.2.3.4",
+          sensor_unit: "",
+          sensor_divisor: 1,
+          metadata: %{"limit_low" => -1}
+        })
+        |> Repo.insert!()
+
+      {:ok, check} =
+        Monitoring.create_check(%{
+          organization_id: device.organization_id,
+          device_id: device.id,
+          name: "Connected Clients",
+          check_type: "snmp_sensor",
+          source_type: "auto_discovery",
+          source_id: sensor.id,
+          config: %{
+            "sensor_type" => "clients",
+            "sensor_oid" => ".1.2.3.4",
+            "sensor_unit" => ""
+          }
+        })
+
+      expect(SnmpMock, :get, fn _ip, _oid, _opts ->
+        {:ok, {:integer, 0}}
+      end)
+
+      assert {:ok, response} = SnmpSensorExecutor.execute(check)
+      assert response.value == 0.0
+      # limit_low is -1, so 0 > -1, meaning no low threshold triggered
+      # But the default clients check kicks in: 0 clients = CRITICAL
+      assert response.status == 2
+    end
+
     test "formats count sensor output as integer", %{device: device, snmp_device: snmp_device} do
       sensor =
         %Sensor{}