feat: add tag subscription

- add GraphQL subscription for tag creation events
- add test coverage for tag subscriptions
  to ensure functionality works as expected

Signed-off-by: Osman Hadzic <osman.hadzic@secomind.com>

Author: osmanhadzic

backend/lib/edgehog/labeling/tag.ex

@@ -37,6 +37,14 @@ defmodule Edgehog.Labeling.Tag do
   graphql do
     type :tag
 
+    subscriptions do
+      pubsub EdgehogWeb.Endpoint
+
+      subscribe :tag do
+        action_types [:create]
+      end
+    end
+
     paginate_relationship_with device_tags: :relay
   end
 

backend/test/edgehog_web/schema/subscriptions/labeling/tags_subscriptions_test.exs

@@ -0,0 +1,61 @@
+#
+# This file is part of Edgehog.
+#
+# Copyright 2026 SECO Mind Srl
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+defmodule EdgehogWeb.Schema.Subscriptions.Labeling.TagsSubscriptionsTest do
+  @moduledoc false
+  use EdgehogWeb.SubsCase
+
+  import Edgehog.LabelingFixtures
+
+  describe "Tag subscription" do
+    test "receive data on tag creation", %{socket: socket, tenant: tenant} do
+      subscribe(socket)
+
+      tag = tag_fixture(tenant: tenant)
+
+      assert_push "subscription:data", push
+
+      assert_created "tag", tag_data, push
+
+      assert tag_data["id"] == AshGraphql.Resource.encode_relay_id(tag)
+      assert tag_data["name"] == tag.name
+    end
+
+    defp subscribe(socket, opts \\ []) do
+      default_sub_gql = """
+      subscription Tag {
+      tag {
+          created {
+              id
+              name
+          }
+      }
+      }
+      """
+
+      sub_gql = Keyword.get(opts, :query, default_sub_gql)
+
+      ref = push_doc(socket, sub_gql)
+      assert_reply ref, :ok, %{subscriptionId: subscription_id}
+
+      subscription_id
+    end
+  end
+end

backend/test/support/fixtures/labeling_fixtures.ex

@@ -0,0 +1,51 @@
+#
+# This file is part of Edgehog.
+#
+# Copyright 2026 SECO Mind Srl
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+defmodule Edgehog.LabelingFixtures do
+  @moduledoc """
+  This module defines test helpers for creating
+  entities via the `Edgehog.Labeling` context.
+  """
+
+  @doc """
+  Generate a unique tag name.
+  """
+  def unique_tag_name, do: "tag_#{System.unique_integer([:positive])}"
+
+  @doc """
+  Generate a tag.
+
+  ## Options
+
+    * `:tenant` - Required. The tenant for the tag.
+  """
+  def tag_fixture(opts \\ []) do
+    {tenant, opts} = Keyword.pop!(opts, :tenant)
+
+    params =
+      Enum.into(opts, %{
+        name: unique_tag_name()
+      })
+
+    Edgehog.Labeling.Tag
+    |> Ash.Changeset.for_create(:create, params, tenant: tenant)
+    |> Ash.create!()
+  end
+end