One deploy cost two slow hours at checkout. Rolling it back fixed it.

24 points, 00:00 to 23:00, from 169 ms to 842 ms. Note 1, at 09:00: Morning peak (238 ms). EU traffic tops out; p95 stays under 240 ms. Note 2, at 14:00: Deploy 4812 (+281%). An N+1 query in /orders sent p95 to 842 ms. Note 3, at 16:00: Rolled back to 4811 (−75%). Under 210 ms again by 16:00.