Creates an account-owned ten-minute lease for a canonical weighted book and returns the synthetic_id to subscribe to at wss://stream.kairos.trade with provider/topic synthetic.

Uses the caller's existing Kairos credential triple; no separate Synthetic Books credential, scope, or account allowlist is required. The full API-key triple also satisfies the mutation gate automatically.

Equivalent canonical definitions share a data-plane materialization but receive distinct account-owned lease UUIDs. Maximum 15 legs, depth 50, 25 active leases per user, and 30 create requests/minute/user by default.

{
  "legs": [
    {
      "venue": "polymarket",
      "weight": "-1"
    }
  ],
  "depth": 50
}

{
  "synthetic_id": "syn_0123456789abcdef",
  "ttl_ms": 600000
}