Validate ActionText associations during import check phase

ActionTextRichTextRecordSet now calls check_associations_dont_exist to
ensure imported ActionText records only reference records within the
same import, matching the behavior of the parent RecordSet class.

test/models/account/data_transfer/action_text_rich_text_record_set_test.rb

@@ -0,0 +1,44 @@
+require "test_helper"
+
+class Account::DataTransfer::ActionTextRichTextRecordSetTest < ActiveSupport::TestCase
+  test "check rejects ActionText record referencing existing card in another account" do
+    importing_account = Account.create!(name: "Importing Account", external_account_id: 99999999)
+
+    victim_card = cards(:logo)
+    assert_not_equal importing_account.id, victim_card.account_id, "Card must belong to a different account"
+
+    # Create a malicious ActionText record that points to the victim's card
+    malicious_action_text_data = {
+      "id" => "malicious_action_text_id_12345",
+      "account_id" => importing_account.id,
+      "record_type" => "Card",
+      "record_id" => victim_card.id,
+      "name" => "description",
+      "body" => "<p>Injected content from attacker</p>",
+      "created_at" => Time.current.iso8601,
+      "updated_at" => Time.current.iso8601
+    }
+
+    tempfile = Tempfile.new([ "malicious_import", ".zip" ])
+    tempfile.binmode
+
+    writer = ZipFile::Writer.new(tempfile)
+    writer.add_file("data/action_text_rich_texts/#{malicious_action_text_data['id']}.json", malicious_action_text_data.to_json)
+    writer.close
+    tempfile.rewind
+
+    reader = ZipFile::Reader.new(tempfile)
+
+    record_set = Account::DataTransfer::ActionTextRichTextRecordSet.new(importing_account)
+
+    error = assert_raises(Account::DataTransfer::RecordSet::IntegrityError) do
+      record_set.check(from: reader)
+    end
+
+    assert_match(/references existing record.*Card.*#{victim_card.id}/i, error.message)
+  ensure
+    tempfile&.close
+    tempfile&.unlink
+    importing_account&.destroy
+  end
+end