Phase 0 scaffold: arcadia-cloud Phoenix service

API-only Phoenix 1.8 project for cloud-ops, inventory, billing, and
provisioning sagas. Validates arcadia JWTs via shared Guardian secret
(verify-only; arcadia-app remains the issuer).

Deps beyond default Phoenix: guardian, cors_plug, oban, req.
Postgres on local port 5433 per arcadia stack convention.
Endpoint runs on :4005.

Endpoints:
- GET /api/health         — public, returns service identifier
- GET /api/v1/inventory   — auth-gated, returns empty list (phase 0 stub)

Oban configured with the queues phase 1+ will need:
provisioning / cloud_sync_fast|full|slow / cloud_billing / metering.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/arcadia_cloud_web/controllers/error_json_test.exs

@@ -0,0 +1,12 @@
+defmodule ArcadiaCloudWeb.ErrorJSONTest do
+  use ArcadiaCloudWeb.ConnCase, async: true
+
+  test "renders 404" do
+    assert ArcadiaCloudWeb.ErrorJSON.render("404.json", %{}) == %{errors: %{detail: "Not Found"}}
+  end
+
+  test "renders 500" do
+    assert ArcadiaCloudWeb.ErrorJSON.render("500.json", %{}) ==
+             %{errors: %{detail: "Internal Server Error"}}
+  end
+end

test/support/conn_case.ex

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+defmodule ArcadiaCloudWeb.ConnCase do
+  @moduledoc """
+  This module defines the test case to be used by
+  tests that require setting up a connection.
+
+  Such tests rely on `Phoenix.ConnTest` and also
+  import other functionality to make it easier
+  to build common data structures and query the data layer.
+
+  Finally, if the test case interacts with the database,
+  we enable the SQL sandbox, so changes done to the database
+  are reverted at the end of every test. If you are using
+  PostgreSQL, you can even run database tests asynchronously
+  by setting `use ArcadiaCloudWeb.ConnCase, async: true`, although
+  this option is not recommended for other databases.
+  """
+
+  use ExUnit.CaseTemplate
+
+  using do
+    quote do
+      # The default endpoint for testing
+      @endpoint ArcadiaCloudWeb.Endpoint
+
+      use ArcadiaCloudWeb, :verified_routes
+
+      # Import conveniences for testing with connections
+      import Plug.Conn
+      import Phoenix.ConnTest
+      import ArcadiaCloudWeb.ConnCase
+    end
+  end
+
+  setup tags do
+    ArcadiaCloud.DataCase.setup_sandbox(tags)
+    {:ok, conn: Phoenix.ConnTest.build_conn()}
+  end
+end

test/support/data_case.ex

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+defmodule ArcadiaCloud.DataCase do
+  @moduledoc """
+  This module defines the setup for tests requiring
+  access to the application's data layer.
+
+  You may define functions here to be used as helpers in
+  your tests.
+
+  Finally, if the test case interacts with the database,
+  we enable the SQL sandbox, so changes done to the database
+  are reverted at the end of every test. If you are using
+  PostgreSQL, you can even run database tests asynchronously
+  by setting `use ArcadiaCloud.DataCase, async: true`, although
+  this option is not recommended for other databases.
+  """
+
+  use ExUnit.CaseTemplate
+
+  using do
+    quote do
+      alias ArcadiaCloud.Repo
+
+      import Ecto
+      import Ecto.Changeset
+      import Ecto.Query
+      import ArcadiaCloud.DataCase
+    end
+  end
+
+  setup tags do
+    ArcadiaCloud.DataCase.setup_sandbox(tags)
+    :ok
+  end
+
+  @doc """
+  Sets up the sandbox based on the test tags.
+  """
+  def setup_sandbox(tags) do
+    pid = Ecto.Adapters.SQL.Sandbox.start_owner!(ArcadiaCloud.Repo, shared: not tags[:async])
+    on_exit(fn -> Ecto.Adapters.SQL.Sandbox.stop_owner(pid) end)
+  end
+
+  @doc """
+  A helper that transforms changeset errors into a map of messages.
+
+      assert {:error, changeset} = Accounts.create_user(%{password: "short"})
+      assert "password is too short" in errors_on(changeset).password
+      assert %{password: ["password is too short"]} = errors_on(changeset)
+
+  """
+  def errors_on(changeset) do
+    Ecto.Changeset.traverse_errors(changeset, fn {message, opts} ->
+      Regex.replace(~r"%{(\w+)}", message, fn _, key ->
+        opts |> Keyword.get(String.to_existing_atom(key), key) |> to_string()
+      end)
+    end)
+  end
+end

test/test_helper.exs

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+ExUnit.start()
+Ecto.Adapters.SQL.Sandbox.mode(ArcadiaCloud.Repo, :manual)