Max instance cap reached

A surprise viral moment drives 8x normal traffic to your storefront API. The autoscaler ramps quickly and then flatlines: the fleet is pinned at its configured maximum of 100 instances, every instance is at ~95% CPU, and excess requests queue and time out. The scaling event log shows repeated 'desired exceeds max, capped at 100' messages. This is real, legitimate traffic, no retry storm, no misconfig. How do you triage and keep the store usable through the surge?