[Pre-SEP] CCTP inbound deposits for Stellar anchors

[Dyjuen]

Idea

Standardize how Stellar anchors accept inbound USDC via Circle CCTP: burn on a source chain, wait for the signed Iris attestation, mint Stellar USDC through a Soroban forwarder, credit the destination.

Why

CCTP connects Stellar (domain 27) to 29 source chains, but every anchor re-solves the same plumbing: 6-decimal vs 7-decimal amounts, EVM address formats vs G... StrKeys, attestation polling/verification, domain mapping, destination trustlines. A shared SEP fixes wire format + discovery so one integration serves every anchor.

Draft spec

Full draft: https://github.com/stellar/stellar-protocol/pull/2031/files (ecosystem/sep_cctp_inbound_deposits.md)

Covers: transfer lifecycle, exact 6-to-7 conversion (BigInt, net-of-fee receipts), stellar.toml [CCTP] + [[CURRENCIES]] metadata, mint_and_forward interface, (sourceDomain, burnTxHash) replay store, opt-in capped trustline creation.

Reference implementation

• Core SDK: https://github.com/Elmanda1/anchorcctp-sdk/tree/main/packages/core
• CLI: https://github.com/Elmanda1/anchorcctp-sdk/tree/main/packages/cli
• Demo: https://github.com/Elmanda1/anchorcctp-sdk/tree/main/apps/demo

Ask

Feedback on scope (inbound-only for v0.0.1?), the [CCTP] metadata fields, and whether SEP-6/24 integration should be normative or informative. Once there is rough consensus I will mark PR #2031 ready for review and request merge/numbering.