fix(examples): multi_rail_merchant emits complete x402 v2 accepts entries

Mirror of node-commerce d39b086: examples/multi_rail_merchant.py declared
x402_version=2 but emitted accepts entries with only {scheme, network, payTo}
— missing required `amount` + `asset` fields. Strict x402 parsers would
reject. Adds atomic USDC amount + asset addr (from the USDC registry) +
maxTimeoutSeconds to both rail entries.

483 tests + ruff + ty green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vvillait88

examples/multi_rail_merchant.py

@@ -60,6 +60,7 @@
 )
 from agentscore_commerce.identity.fastapi import AgentScoreGate, get_assess_data
 from agentscore_commerce.payment import (
+    USDC,
     PaymentRequiredHeaderInput,
     ProcessX402SettleInput,
     ValidateX402NetworkConfigInput,
@@ -220,8 +221,22 @@ async def purchase(request: Request, assess: dict = Depends(get_assess_data)):
             x402=PaymentRequiredHeaderInput(
                 x402_version=2,
                 accepts=[
-                    {"scheme": "exact", "network": X402_BASE_NETWORK, "payTo": deposit_addresses["base"]},
-                    {"scheme": "exact", "network": X402_SVM_NETWORK, "payTo": deposit_addresses["solana"]},
+                    {
+                        "scheme": "exact",
+                        "network": X402_BASE_NETWORK,
+                        "amount": str(round(float(total_usd) * 1_000_000)),
+                        "asset": USDC.base.mainnet.address,
+                        "payTo": deposit_addresses["base"],
+                        "maxTimeoutSeconds": 300,
+                    },
+                    {
+                        "scheme": "exact",
+                        "network": X402_SVM_NETWORK,
+                        "amount": str(round(float(total_usd) * 1_000_000)),
+                        "asset": USDC.solana.mainnet.mint,
+                        "payTo": deposit_addresses["solana"],
+                        "maxTimeoutSeconds": 300,
+                    },
                 ],
                 resource={"url": str(request.url), "mimeType": "application/json"},
             ),