We rotated our JWKS without overlap. Here is the 4-minute window that broke prod.

The on-call alert at 02:14 said auth_5xx_rate spiked from 0.01 to 31.4 . Not a deploy window. Not a traffic spike. Just thirty-one percent of authenticated requests failing for ~four minutes, then back to baseline. The cause was a JWKS rotation on the issuer side. New keys came in. Old keys went out. Caches in our service didn't refresh fast enough. Tokens signed with the new key were rejected because the verifier still held the old JWKS. Tokens signed with the old key were rejected because the