sandbox_admission_unavailable
The conversation-slot registry this deployment started with cannot hold lane reservations, so sandbox sessions have neither a per-account concurrency ceiling nor a platform one. Fail-closed, in the same family as slot_registry_unavailable (§9.9): admitting unbounded sessions is the state admission control exists to end.
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/sandbox_admission_unavailable",
"title": "…",
"status": 503,
"detail": "…",
"instance": "/v1/…"
}