Prepare an order for signing

Step 1 of 3. Validates the order, builds the Canton transaction and has it prepared against the ledger. NOTHING IS ON THE BOOK when this returns. Next: sign data.signing.preparedTransactionHash and POST the signature to data.signing.submitUrl (see the Submit tag). The prepared transaction has a 5 minute TTL. Prepare only what the client intends to sign immediately. Typical latency 10 to 13 seconds against a 30 second server ceiling. SERIALISE PER PARTY. Preparing a second order while a previous one is still awaiting ledger confirmation can be rejected with LEDGER_COMMAND_REJECTED ("Calden is still waiting for ledger confirmation"). Reproduced under network degradation; no safe concurrency limit has been established under healthy conditions. Submit, confirm via GET /orders, then prepare the next.

curl -X POST "https://example.com/orders" \  -H "Content-Type: application/json" \  -d '{    "pair": "CBTC/CC",    "side": "BUY",    "type": "LIMIT",    "quantity": "0.01"  }'

{  "ok": true,  "data": {    "order": {      "clientOrderId": "string",      "pair": "string",      "side": "BUY",      "type": "string",      "price": "string",      "quantity": "string",      "filledQuantity": "string",      "status": "string",      "contractId": "string",      "createdAt": "2019-08-24T14:15:22Z",      "correlationId": "string",      "caldenIntentId": "string",      "providerFeeAmount": "0",      "providerFeeSymbol": "CC"    },    "signing": {      "requiresSignature": true,      "preparedTransactionHash": "string",      "hashingSchemeVersion": "HASHING_SCHEME_VERSION_V2",      "submitUrl": "http://example.com",      "submitToken": "string",      "commandId": "string",      "status": "PENDING_SIGNATURE",      "signingUrl": "string",      "prepared": {}    }  }}