fix validation behaviour

lib/mv/membership/member/validations/email_not_used_by_other_user.ex

@@ -1,26 +1,37 @@
 defmodule Mv.Membership.Member.Validations.EmailNotUsedByOtherUser do
   @moduledoc """
   Validates that the member's email is not already used by another user.
-  Allows syncing with linked user (excludes linked user from check).
+  Only validates when:
+  - Member is already linked to a user (user != nil) AND email is changing
+  - Member is being linked to a user (user relationship is changing)
+
+  This allows creating members with the same email as unlinked users.
   """
   use Ash.Resource.Validation
 
   @impl true
   def validate(changeset, _opts, _context) do
-    case Ash.Changeset.fetch_change(changeset, :email) do
-      {:ok, new_email} ->
-        linked_user_id = get_linked_user_id(changeset.data)
-        check_email_uniqueness(new_email, linked_user_id)
+    email_changing? = Ash.Changeset.changing_attribute?(changeset, :email)
 
-      :error ->
-        :ok
+    linked_user_id = get_linked_user_id(changeset.data)
+    is_linked? = not is_nil(linked_user_id)
+
+    # Only validate if member is already linked AND email is changing
+    # Do NOT validate when member is being linked (email will be overridden from user)
+    should_validate? = is_linked? and email_changing?
+
+    if should_validate? do
+      new_email = Ash.Changeset.get_attribute(changeset, :email)
+      check_email_uniqueness(new_email, linked_user_id)
+    else
+      :ok
     end
   end
 
-  defp check_email_uniqueness(new_email, exclude_user_id) do
+  defp check_email_uniqueness(email, exclude_user_id) do
     query =
       Mv.Accounts.User
-      |> Ash.Query.filter(email == ^new_email)
+      |> Ash.Query.filter(email == ^email)
       |> maybe_exclude_id(exclude_user_id)
 
     case Ash.read(query) do
@@ -28,7 +39,7 @@ defmodule Mv.Membership.Member.Validations.EmailNotUsedByOtherUser do
         :ok
 
       {:ok, _} ->
-        {:error, field: :email, message: "is already used by another user", value: new_email}
+        {:error, field: :email, message: "is already used by another user", value: email}
 
       {:error, _} ->
         :ok