Fix email uniqueness check ignoring discarded members

The `email_must_be_unique` validation queried all members, including
discarded ones. This blocked email reuse during the 30-day window
before anonymization clears the email. Scope the query to `.kept`.

Author: thibaudgg

app/models/member.rb

@@ -253,7 +253,7 @@ def set_default_waiting_delivery_cycle
 
   def email_must_be_unique
     emails_array.each do |email|
-      if Member.where.not(id: id).including_email(email).exists?
+      if Member.kept.where.not(id: id).including_email(email).exists?
         errors.add(:emails, :taken)
         break
       end

test/models/member_registration_test.rb

@@ -117,18 +117,17 @@ def register(member, params)
     assert_equal 30, member.annual_fee
   end
 
-  test "cannot reuse discarded member" do
+  test "can reuse discarded member email" do
     member = discardable_member
     email = member.emails_array.first
     member.discard
 
-    new_member = build_member(emails: email)
-    registration = MemberRegistration.new(new_member, {})
+    new_member = build_member(emails: email, phones: "+41 79 999 99 99", waiting_basket_size_id: 0)
+    new_member.public_create = true
 
-    # Should not find the discarded member for reuse
-    assert_not registration.save
-    # The email is still "taken" by the discarded member
-    assert new_member.errors.of_kind?(:emails, :taken)
+    # Email is still in the DB but discarded members should not block reuse
+    assert_not_empty Member.including_email(email)
+    assert_predicate new_member, :valid?, new_member.errors.full_messages.join(", ")
   end
 
   test "can use email after member is anonymized" do

test/models/member_test.rb

@@ -94,6 +94,13 @@ class MemberTest < ActiveSupport::TestCase
     assert_not Member.new(emails: "john@example.com").valid?
   end
 
+  test "validates email uniqueness ignores discarded members" do
+    member = members(:mary)
+    member.update_columns(state: "inactive", discarded_at: Time.current, emails: "reuse@example.com")
+
+    assert build_member(emails: "reuse@example.com").valid?
+  end
+
   test "validates annual_fee to be greater or equal to zero" do
     assert build_member(annual_fee: nil).valid?
     assert build_member(annual_fee: 0).valid?