actionmailer

class RegistrationsController < ApplicationController
  def new
    @user = User.new
  end

  def create

class EmailDedupService
  DEFAULT_TTL = 5.minutes.to_i

  def self.claim(fingerprint, ttl: DEFAULT_TTL)
    key = "email_dedup:#{fingerprint}"
    # Atomic set-if-absent with expiry; returns true only for the first caller.