ESP API latency tracked

ESP API latency is a leading indicator of outages and rate-limit throttling. A call that normally completes in 80 ms suddenly taking 4 seconds means the ESP is struggling — but without per-call timing recorded to a metrics system or log, the only way you discover the degradation is through user reports or queue backlog growth. ISO 25010 performance-efficiency requires that time-behaviour is measurable. Missing timing on error paths is especially dangerous: slow errors are the most likely signal of an impending outage.

Wrap the ESP send call in your ESP adapter (e.g., src/lib/email/providers/sendgrid.ts) so both success and error paths record the duration:

const start = Date.now()
try {
  await esp.send(message)
  metrics.histogram('esp_send_duration_ms', Date.now() - start, { result: 'success' })
} catch (err) {
  metrics.histogram('esp_send_duration_ms', Date.now() - start, { result: 'error' })
  throw err
}

Every call site must record timing — partial instrumentation on success paths only will not satisfy this check.