Atomic NFT Delivery-vs-Payment

# pip install xrpl-py httpx
import httpx
from xrpl.clients import JsonRpcClient
from xrpl.models.transactions import NFTokenCreateOffer, NFTokenAcceptOffer
from xrpl.models.requests import AccountNFTs
from xrpl.wallet import Wallet
from xrpl.transaction import submit_and_wait
from xrpl.utils import xrp_to_drops

REFEREE        = "https://mcp.cryptovault.co.uk"
XRPL_NODE      = "https://s1.ripple.com:51234/"

seller_wallet  = Wallet.from_seed("sSELLER_SEED_HERE")
buyer_address  = "rBUYER_ADDRESS_HERE"
client         = JsonRpcClient(XRPL_NODE)

ESCROW_ID      = "NFT-XXXX"   # escrow_id shared by the buyer
NFT_TOKEN_ID   = "000800006B6B..."

# Step 1: Create a sell offer for 0 XRP (free transfer to specific buyer)
offer_tx = NFTokenCreateOffer(
    account      = seller_wallet.address,
    nftoken_id   = NFT_TOKEN_ID,
    amount       = "0",                   # buyer already paid via escrow
    destination  = buyer_address,           # restricted to the buyer only
    flags        = 1,                      # tfSellNFToken
)
offer_result = submit_and_wait(offer_tx, client, seller_wallet).result
offer_id = next(
    n["CreatedNode"]["LedgerIndex"]
    for n in offer_result["meta"]["AffectedNodes"]
    if n.get("CreatedNode", {}).get("LedgerEntryType") == "NFTokenOffer"
)
print(f"Sell offer created: {offer_id}")

# Step 2: Buyer accepts the offer — run this as the buyer
buyer_wallet = Wallet.from_seed("sBUYER_SEED")   # buyer's XRPL wallet seed
accept_tx = NFTokenAcceptOffer(
    account=buyer_wallet.address, nftoken_sell_offer=offer_id)
submit_and_wait(accept_tx, client, buyer_wallet)
print("NFT transferred to buyer wallet")

# -- (once buyer has accepted and NFT is in their wallet) --

# Step 3: Verify the NFT is now in the buyer's wallet
nfts = client.request(AccountNFTs(account=buyer_address)).result["account_nfts"]
owned = any(n["NFTokenID"] == NFT_TOKEN_ID for n in nfts)
assert owned, "NFT not yet in buyer wallet — wait for acceptance"
print("NFT confirmed in buyer wallet. Submitting proof...")

# Step 4: Submit proof to AgentTrust — payment releases automatically on PASS
result = httpx.post(f"{REFEREE}/evaluate", json={
    "escrow_id": ESCROW_ID,
    "work": (
        f"NFT transfer complete.\n"
        f"Token ID: {NFT_TOKEN_ID}\n"
        f"Current owner (buyer): {buyer_address}\n"
        f"Sell offer accepted: {offer_id}\n"
        f"NFT is confirmed in the buyer's wallet on the XRP Ledger."
    ),
}, timeout=120).json()

print(f"Verdict: {result['verdict']} | Score: {result['score']}/100")
# PASS → EscrowFinish submitted on-chain automatically → seller receives XRP