vocapablework_reserved
Someone - a teammate, you on another device, or an AI job - already holds the work on this customer. holder names them, expires_at says until when, next_action says what to do instead, and reservation_id is your own lease when the holder is you.
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/work_reserved",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}