feat: join request backend

lib/membership/membership.ex

@@ -78,6 +78,52 @@ defmodule Mv.Membership do
       define :list_member_groups, action: :read
       define :destroy_member_group, action: :destroy
     end
+
+    resource Mv.Membership.JoinRequest do
+      define :list_join_requests, action: :read
+      define :get_join_request, action: :read, get_by: [:id]
+      define :update_join_request, action: :update
+      define :destroy_join_request, action: :destroy
+    end
+  end
+
+  # Idempotent confirm: implemented in code so duplicate token returns {:ok, existing} (concept §2.3.2)
+  @doc """
+  Creates a JoinRequest after confirmation link click (public action with actor: nil).
+
+  Idempotent: if a JoinRequest with the same `confirmation_token_hash` already exists,
+  returns `{:ok, existing}` instead of creating a duplicate (per concept §2.3.2).
+  """
+  def confirm_join_request(attrs, opts \\ []) do
+    hash = attrs[:confirmation_token_hash] || attrs["confirmation_token_hash"]
+
+    if hash do
+      case get_join_request_by_confirmation_token_hash!(hash, opts) do
+        nil -> do_confirm_join_request(attrs, opts)
+        existing -> {:ok, existing}
+      end
+    else
+      do_confirm_join_request(attrs, opts)
+    end
+  end
+
+  defp do_confirm_join_request(attrs, opts) do
+    Mv.Membership.JoinRequest
+    |> Ash.Changeset.for_create(:confirm, attrs)
+    |> Ash.create(Keyword.put(opts, :domain, __MODULE__))
+  end
+
+  defp get_join_request_by_confirmation_token_hash!(hash, opts) do
+    opts = Keyword.put(opts, :domain, __MODULE__)
+
+    Mv.Membership.JoinRequest
+    |> Ash.Query.filter(confirmation_token_hash == ^hash)
+    |> Ash.read_one(opts)
+    |> case do
+      {:ok, %Mv.Membership.JoinRequest{} = existing} -> existing
+      {:ok, nil} -> nil
+      _ -> nil
+    end
   end
 
   # Singleton pattern: Get the single settings record