cc_state_transition_invalid
CC2-R1: the agent state transition table does not list this change (e.g. declaring a state while on a call - choose a next status; a supervisor signing out an agent on a call is refused until the call ends, CC3-R5; ringing → not ready). The detail names the states.
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/cc_state_transition_invalid",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}