atlas, on the issue: swarm-controller's problem+json conversion merged
(58588a68, closing hyperhive#3412 which this comment referenced as an
in-flight fix). Every first-party API is RFC 9457 now, so the non-JSON
fallback path is not backend-transition compatibility anymore — it's for
bodies this repo didn't author (a caller pointed elsewhere, or an
nginx-synthesised 502/504 that never reaches our handlers). Comment
updated to say that instead of pointing at a transition that's already
finished.
62d1c6224b