refactor: replace Task.async_stream with Oban jobs for discovery

Changed discover_all/1 to enqueue individual Oban jobs instead of using
Task.async_stream for better error visibility and resilience.

Benefits:
- Errors are visible in Oban dashboard with full stack traces
- Automatic retries on failure via Oban
- Jobs persist across pod restarts
- No more silent failures from Task crashes
- Better concurrency control via Oban queue configuration

Changes:
- discover_all/1 now enqueues DiscoveryWorker jobs and returns immediately
- Return type changed from %{success, failed, errors} to %{enqueued, failed, errors}
- Updated tests to match new async behavior
- Added DiscoveryWorker alias to Discovery module

All tests passing (3,625 tests, 0 failures).

lib/towerops/snmp/discovery.ex

@@ -31,6 +31,7 @@ defmodule Towerops.Snmp.Discovery do
   alias Towerops.Snmp.Sensor
   alias Towerops.Snmp.Storage
   alias Towerops.Snmp.Vlan
+  alias Towerops.Workers.DiscoveryWorker
 
   require Logger
 
@@ -81,7 +82,7 @@ defmodule Towerops.Snmp.Discovery do
   @type profile :: module() | {:yaml, map()}
 
   @type discovery_summary :: %{
-          success: non_neg_integer(),
+          enqueued: non_neg_integer(),
           failed: non_neg_integer(),
           errors: [term()]
         }
@@ -249,8 +250,14 @@ defmodule Towerops.Snmp.Discovery do
   end
 
   @doc """
-  Runs discovery for all SNMP-enabled devices in an organization.
-  Returns a summary of successful and failed discoveries.
+  Enqueues Oban discovery jobs for all SNMP-enabled devices in an organization.
+
+  Returns immediately after enqueuing jobs. Job status can be monitored via Oban dashboard.
+
+  ## Examples
+
+      iex> discover_all(org_id)
+      {:ok, %{enqueued: 10, failed: 0}}
   """
   @spec discover_all(String.t()) :: {:ok, discovery_summary()}
   def discover_all(org_id) do
@@ -260,28 +267,23 @@ defmodule Towerops.Snmp.Discovery do
       |> where([e, s], s.organization_id == ^org_id and e.snmp_enabled == true)
       |> Repo.all()
 
-    Logger.info("Starting SNMP discovery for #{length(device_list)} devices in org #{org_id}")
+    Logger.info("Enqueuing SNMP discovery for #{length(device_list)} devices in org #{org_id}")
 
+    # Enqueue Oban jobs for each device
     results =
-      device_list
-      |> Task.async_stream(
-        &discover_device/1,
-        max_concurrency: 5,
-        timeout: 60_000,
-        on_timeout: :kill_task
-      )
-      |> Enum.reduce(%{success: 0, failed: 0, errors: []}, fn
-        {:ok, {:ok, _device}}, acc ->
-          %{acc | success: acc.success + 1}
+      Enum.reduce(device_list, %{enqueued: 0, failed: 0, errors: []}, fn device, acc ->
+        case DiscoveryWorker.enqueue(device.id) do
+          {:ok, _job} ->
+            %{acc | enqueued: acc.enqueued + 1}
 
-        {:ok, {:error, reason}}, acc ->
-          %{acc | failed: acc.failed + 1, errors: [reason | acc.errors]}
-
-        {:exit, :timeout}, acc ->
-          %{acc | failed: acc.failed + 1, errors: [:timeout | acc.errors]}
+          {:error, reason} ->
+            Logger.error("Failed to enqueue discovery for device #{device.id}: #{inspect(reason)}")
+            %{acc | failed: acc.failed + 1, errors: [reason | acc.errors]}
+        end
       end)
 
-    Logger.info("Discovery completed: #{results.success} succeeded, #{results.failed} failed")
+    Logger.info("Discovery jobs enqueued: #{results.enqueued} succeeded, #{results.failed} failed")
+
     {:ok, results}
   end
 

test/towerops/snmp/discovery_test.exs

@@ -795,7 +795,7 @@ defmodule Towerops.Snmp.DiscoveryTest do
   describe "discover_all/1" do
     test "discovers multiple devices concurrently", %{organization: organization, site: site} do
       # Create multiple SNMP-enabled devices
-      {:ok, device1} =
+      {:ok, _device1} =
         Towerops.Devices.create_device(%{
           name: "Device 1",
           ip_address: "192.168.1.10",
@@ -806,7 +806,7 @@ defmodule Towerops.Snmp.DiscoveryTest do
           snmp_port: 161
         })
 
-      {:ok, device2} =
+      {:ok, _device2} =
         Towerops.Devices.create_device(%{
           name: "Device 2",
           ip_address: "192.168.1.11",
@@ -847,17 +847,13 @@ defmodule Towerops.Snmp.DiscoveryTest do
 
       assert {:ok, summary} = Discovery.discover_all(organization.id)
 
-      # Should only discover SNMP-enabled devices
-      assert summary.success == 2
+      # Should enqueue jobs for SNMP-enabled devices
+      assert summary.enqueued == 2
       assert summary.failed == 0
-
-      # Verify devices were created
-      assert Repo.get_by(Device, device_id: device1.id)
-      assert Repo.get_by(Device, device_id: device2.id)
     end
 
     test "handles mixed success and failure", %{organization: organization, site: site} do
-      {:ok, device1} =
+      {:ok, _device1} =
         Towerops.Devices.create_device(%{
           name: "Good Device",
           ip_address: "192.168.1.20",
@@ -904,13 +900,9 @@ defmodule Towerops.Snmp.DiscoveryTest do
 
       assert {:ok, summary} = Discovery.discover_all(organization.id)
 
-      assert summary.success == 1
-      assert summary.failed == 1
-      # Device that fails initial responsiveness check is marked as unresponsive
-      assert :device_unresponsive in summary.errors
-
-      # Verify only good device was created
-      assert Repo.get_by(Device, device_id: device1.id)
+      # Both devices should be enqueued (Oban jobs will handle success/failure)
+      assert summary.enqueued == 2
+      assert summary.failed == 0
     end
 
     test "updates device name from SNMP sysName when device name is empty", %{