Feature Request: Add gasless USDC delivery guide for CCTP bridge completion (relay pattern)

[osr21]

Feature Request: Gasless USDC delivery guide for CCTP + Base Mainnet

Docs section: Payments → CCTP / Cross-Chain

---

What's missing

Base's four product pillars include Payments and the Solana Bridge (CCTP-based). The current docs explain how to initiate a CCTP burn on the source chain, but there's no guide covering the last mile: automatically completing delivery on Base after the attestation is ready.

Today, users who bridge USDC to Base must:

1. Wait for Circle's attestation API to return complete
2. Manually (or programmatically) call receiveMessage on the Base MessageTransmitter contract
3. Pay ETH gas to do so — a significant UX barrier for users who don't yet hold ETH on Base

This gap is especially relevant for the Base Solana Bridge, where recipients are often new-to-Base users with zero ETH.

---

Proposed docs page

Title: "Auto-complete USDC delivery after a CCTP bridge (gasless relay)"

Covers:

• How CCTP v1 works end-to-end (burn → attest → receive)
• Polling Circle's attestation API (https://iris-api.circle.com/attestations/{messageHash})
• Calling receiveMessage on Base's MessageTransmitter (0x1682Ae6375C4E4A97e4B583BC394c861A46D8962)
• A relay pattern where the relayer pays ETH gas so the recipient gets USDC with zero friction
• Error handling: nonce-already-used detection (idempotent re-submission), attestation-not-ready polling
• Security: why you should derive destDomain from messageBytes rather than trusting the client

---

Reference implementation

We built this in BasePay (open source, Base Mainnet):

• Full CCTP relay route: https://github.com/osr21/basepay/blob/main/artifacts/api-server/src/routes/cctp.ts
• Handles attestation polling, receiveMessage submission, nonce-already-used idempotency
• Per-chain nonce serialization to prevent gas waste from concurrent relay submissions

Happy to contribute a draft PR to the docs repo if this is something the team would accept. Just wanted to flag the gap first.

---

Why this matters for Base adoption

The Base Solana Bridge launch is a flagship feature. Frictionless USDC arrival — zero ETH required — is the difference between a good bridge UX and a great one. A relay guide here directly supports Base's "bringing the world onchain" mission.

Thanks!