fix: prevent nil boolean error in device edit page

Fixed production bug where visiting the edit page for a device with no
SNMP discovery data would crash with "expected boolean on left-side of
'and', got: nil" error.

The mikrotik_device?/1 function was using && operator which returns nil
when device.snmp_device is nil, instead of returning false. The template
conditional on line 455 requires a proper boolean value.

Changed from:
  device.snmp_device && (...)

To:
  not is_nil(device.snmp_device) and (...)

This ensures the function always returns a boolean (true/false) instead
of potentially returning nil.

Added regression test to verify the page renders correctly when a device
has no SNMP discovery data yet.

Fixes: https://app.honeybadger.io/projects/136860/faults/127120431

lib/towerops_web/live/device_live/form.ex

@@ -180,7 +180,8 @@ defmodule ToweropsWeb.DeviceLive.Form do
 
   defp mikrotik_device?(device) do
     # Check if device is MikroTik based on SNMP discovery data
-    device.snmp_device &&
+    # Must return boolean (not nil) to work with 'and' operator in templates
+    not is_nil(device.snmp_device) and
       (String.contains?(device.snmp_device.manufacturer || "", "MikroTik") ||
          String.contains?(device.snmp_device.sys_descr || "", "RouterOS"))
   end

test/towerops_web/live/device_live/form_test.exs

@@ -1,6 +1,107 @@
 defmodule ToweropsWeb.DeviceLive.FormTest do
   use ToweropsWeb.ConnCase, async: true
 
+  import Phoenix.LiveViewTest
+
+  setup :register_and_log_in_user
+
+  setup %{user: user} do
+    {:ok, organization} =
+      Towerops.Organizations.create_organization(%{name: "Test Org"}, user.id)
+
+    {:ok, site} =
+      Towerops.Sites.create_site(%{
+        name: "Test Site",
+        organization_id: organization.id
+      })
+
+    %{organization: organization, site: site}
+  end
+
+  describe "edit page rendering" do
+    test "renders edit page when device has no SNMP discovery data (bug fix for nil boolean)", %{
+      conn: conn,
+      site: site
+    } do
+      # Regression test for production bug where visiting edit page for a device
+      # with no SNMP discovery data would crash with "expected boolean, got nil"
+      # because mikrotik_device?/1 could return nil instead of false.
+
+      # Create a device without any snmp_device association (before SNMP discovery)
+      {:ok, device} =
+        Towerops.Devices.create_device(%{
+          name: "Test Device",
+          ip_address: "192.168.1.1",
+          site_id: site.id,
+          snmp_enabled: true,
+          snmp_version: "2c",
+          snmp_port: 161,
+          monitoring_enabled: true,
+          check_interval_seconds: 300
+        })
+
+      # Ensure device has no snmp_device (this is the bug condition)
+      device_with_snmp = Towerops.Repo.preload(device, :snmp_device)
+      assert is_nil(device_with_snmp.snmp_device)
+
+      # Visit edit page - should not crash with "expected boolean, got nil" error
+      assert {:ok, _view, html} = live(conn, ~p"/devices/#{device.id}/edit")
+
+      # Page should render successfully
+      assert html =~ "Edit Device"
+      assert html =~ device.name
+    end
+
+    test "renders MikroTik section for superuser when device is MikroTik", %{
+      conn: conn,
+      site: site,
+      user: user
+    } do
+      alias Towerops.Snmp.Device, as: SnmpDevice
+      # Make user a superuser using Ecto.Changeset (standard test pattern)
+      _user =
+        user
+        |> Ecto.Changeset.change(%{is_superuser: true})
+        |> Towerops.Repo.update!()
+
+      # Create a device with MikroTik SNMP discovery data
+      {:ok, device} =
+        Towerops.Devices.create_device(%{
+          name: "MikroTik Router",
+          ip_address: "192.168.1.254",
+          site_id: site.id,
+          snmp_enabled: true,
+          snmp_version: "2c",
+          snmp_port: 161,
+          monitoring_enabled: true,
+          check_interval_seconds: 300
+        })
+
+      # Create SNMP device with MikroTik manufacturer (using Towerops.Snmp.Device schema)
+      _snmp_device =
+        %SnmpDevice{}
+        |> SnmpDevice.changeset(%{
+          device_id: device.id,
+          manufacturer: "MikroTik",
+          sys_descr: "RouterOS 7.8",
+          sys_object_id: "1.3.6.1.4.1.14988.1",
+          sys_uptime: 0,
+          sys_name: "test-router"
+        })
+        |> Towerops.Repo.insert!()
+
+      # Visit edit page
+      {:ok, _view, html} = live(conn, ~p"/devices/#{device.id}/edit")
+
+      # Page should render successfully
+      assert html =~ "Edit Device"
+      assert html =~ device.name
+
+      # MikroTik section SHOULD be visible (superuser + MikroTik device)
+      assert html =~ "MikroTik API Configuration"
+    end
+  end
+
   describe "non_routable_ip?/1" do
     # Access private function via Module.get_attribute or test via public interface
     # Since these are private functions, we test through the validation behavior