Message priority separates transactional from marketing

A single FIFO email queue shared by transactional and marketing sends creates a hidden contention point. A bulk marketing campaign pushing 100,000 jobs can delay a password-reset email by 30 minutes — precisely the window where a user is waiting at the browser. CWE-400 covers uncontrolled resource consumption; sharing a queue is the mechanism by which a marketing send consumes the delivery window for time-sensitive transactional messages. ISO-25010:2011 performance-efficiency.resource-utilization requires that resources are allocated in proportion to priority.

Define separate BullMQ queues and workers for transactional and marketing sends in lib/queues.ts:

export const transactionalQueue = new Queue('email:transactional', { connection })
export const marketingQueue = new Queue('email:marketing', { connection })

const transactionalWorker = new Worker('email:transactional', processEmail, {
  connection,
  concurrency: 10
})

const marketingWorker = new Worker('email:marketing', processEmail, {
  connection,
  concurrency: 2,
  limiter: { max: 100, duration: 1000 }
})

Route sends at the call site based on the email type, not a shared queue name.