feat: use Exq for SNMP discovery background jobs

- Create DiscoveryWorker for handling SNMP device discovery
- Replace Task.start with Exq.enqueue for discovery operations
- Enqueue jobs to 'discovery' queue with device_id parameter
- Add enqueue_discovery/1 helper that falls back to Task.start in test
- Discovery jobs now persistent and retryable via Exq
- Triggered on: new device creation, device update, manual rediscover button

lib/towerops/workers/discovery_worker.ex

@@ -0,0 +1,47 @@
+defmodule Towerops.Workers.DiscoveryWorker do
+  @moduledoc """
+  Background worker for SNMP device discovery.
+
+  Enqueued when:
+  - A new device is created with SNMP enabled
+  - An existing device's SNMP configuration is changed
+  - User manually triggers discovery via "Rediscover Device" button
+
+  Queue: discovery
+  """
+
+  alias Towerops.Devices
+  alias Towerops.Snmp
+
+  require Logger
+
+  @doc """
+  Performs SNMP discovery for a device.
+
+  ## Parameters
+  - device_id: The UUID of the device to discover
+
+  ## Returns
+  - :ok on success
+  - {:error, reason} on failure
+  """
+  def perform(device_id) do
+    Logger.info("Starting SNMP discovery for device #{device_id}")
+
+    device = Devices.get_device!(device_id)
+
+    case Snmp.discover_device(device) do
+      {:ok, _snmp_device} ->
+        Logger.info("SNMP discovery completed successfully for device #{device_id}")
+        :ok
+
+      {:error, reason} ->
+        Logger.error("SNMP discovery failed for device #{device_id}: #{inspect(reason)}")
+        {:error, reason}
+    end
+  rescue
+    Ecto.NoResultsError ->
+      Logger.error("Device #{device_id} not found")
+      {:error, :device_not_found}
+  end
+end

lib/towerops_web/live/device_live/form.ex

@@ -7,6 +7,7 @@ defmodule ToweropsWeb.DeviceLive.Form do
   alias Towerops.Devices.Device, as: DeviceSchema
   alias Towerops.Sites
   alias Towerops.Snmp
+  alias Towerops.Workers.DiscoveryWorker
 
   @impl true
   def mount(params, _session, socket) do
@@ -195,11 +196,8 @@ defmodule ToweropsWeb.DeviceLive.Form do
     device = socket.assigns.device
 
     if device.snmp_enabled do
-      # Run discovery in background
-      _ =
-        Task.start(fn ->
-          Snmp.discover_device(device)
-        end)
+      # Enqueue discovery job
+      enqueue_discovery(device.id)
 
       {:noreply, put_flash(socket, :info, "Discovery started...")}
     else
@@ -277,7 +275,7 @@ defmodule ToweropsWeb.DeviceLive.Form do
 
   defp handle_device_creation(device) do
     if device.snmp_enabled do
-      _ = Task.start(fn -> Snmp.discover_device(device) end)
+      enqueue_discovery(device.id)
       "Device created successfully. SNMP discovery started in background."
     else
       "Device created successfully"
@@ -286,13 +284,24 @@ defmodule ToweropsWeb.DeviceLive.Form do
 
   defp handle_device_update(old_device, device) do
     if should_trigger_snmp_discovery?(old_device, device) do
-      _ = Task.start(fn -> Snmp.discover_device(device) end)
+      enqueue_discovery(device.id)
       "Device updated successfully. SNMP discovery started in background."
     else
       "Device updated successfully"
     end
   end
 
+  # Enqueue discovery job - safe to call in test environment
+  defp enqueue_discovery(device_id) do
+    if Application.get_env(:towerops, :env) == :test do
+      # In test, run synchronously
+      Task.start(fn -> Snmp.discover_device(Devices.get_device!(device_id)) end)
+    else
+      # In dev/prod, enqueue to Exq
+      {:ok, _job} = Exq.enqueue(Exq, "discovery", DiscoveryWorker, [device_id])
+    end
+  end
+
   defp should_trigger_snmp_discovery?(old_device, device) do
     device.snmp_enabled and
       (!old_device.snmp_enabled or