Reference

MCP tools

• start_session — agent, message → sessionId + reply
• send_message — sessionId, message → reply
• end_session — sessionId → ok

Caller-facing error codes

AgentNotFound
SessionNotFound | SessionExpired | SessionStale | SessionInFlight
AuthFailed
RateLimited
PublisherUnreachable
MessageTooLarge
ModelError
MalformedRequest
GatewayInternal

Gateway → publisher wire

POST https://publisher.example/api/orkestrate
Authorization: Bearer <registration secret>
X-Orkestrate-Action: start_session | send_message | end_session | ping
X-Orkestrate-Session-Id: ses_…
X-Orkestrate-Model: <base64url JSON>  // open/send
X-Orkestrate-Caller-Id: <clerk user id>  // optional

Body open/send: { "message": "..." }
Success: { "reply": "..." } or { "ok": true }
GET health: { "ok": true, "protocol": 1 }

What Orkestrate stores

Routing sessions, registrations, encrypted secrets, encrypted caller model keys, usage event counts. No chat transcripts.