Capacity alerts at 80% threshold

Capacity alerts at failure (queue full, ESP quota exceeded) give operators zero time to react — sends are already failing when the alert fires. An 80% threshold alert gives operators time to scale workers, contact the ESP about a quota increase, or delay a non-urgent campaign before the limit is hit. ISO 25010 reliability.operability requires that the system communicates approaching resource exhaustion, not just completed resource exhaustion. The Monitoring & Alerting category checks in this bundle verify that signals are being measured — this check verifies that pre-warning thresholds are configured on those signals.

Add a threshold check in the queue monitoring poller for at least one capacity metric — daily send quota is the most common:

const DAILY_QUOTA = 100_000
const sentToday = await countSentToday()
if (sentToday > DAILY_QUOTA * 0.8) {
  await alertOps(
    `Daily send quota at ${Math.round(sentToday / DAILY_QUOTA * 100)}% — ${DAILY_QUOTA - sentToday} sends remaining`,
    'warning'
  )
}

The threshold value must be explicitly defined in code or configuration — a magic number with no comment explaining it is the limit does not satisfy this check.