caller_request_version_conflict
The request changed since it was read (optimistic-concurrency version mismatch). The detail names the current version; re-read the request and retry with it. Distinct from caller_request_invalid_transition so a portal can tell "refresh and retry" from "someone already resolved this".
Problem shape
Every non-2xx response is an RFC 9457 application/problem+json body. The type URI below is stable and machine-matchable, so branch on the final path segment (the code) and treat the status as redundant confirmation. See the error-handling guide.
{
"type": "https://docs.vocapable.com/errors/caller_request_version_conflict",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}