@PaidEndpoint

Wraps any async FastAPI endpoint with x402 payment logic.

@PaidEndpoint(
    price="0.5 HBAR",
    receiver="0.0.4820193",   # optional, defaults to HEDERA_ACCOUNT_ID
    ttl_seconds=600,          # optional
)
async def my_service(request: Request):
    ...

The decorator:

• Intercepts requests without a valid grant → returns 402 with a signed quote
• Verifies proofs against Mirror Node before invoking your handler
• Rejects duplicate transaction IDs (idempotency)
• Publishes an HCS receipt after every successful call