agent_use_case_immutable
A published agent definition cannot change use_case. Calling purpose determines the consent floor for its immutable versions and any campaign already using them; create a new draft definition for a different purpose.
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/agent_use_case_immutable",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}