feat: add use-refund-protocol skill

[zkasuran]

Summary

Adds use-refund-protocol skill documenting Circle's Refund Protocol — a non-custodial USDC escrow system with dispute resolution on Arc.

What's Covered

• Pay/withdraw lifecycle with configurable lockup periods (0-180 days)
• Three refund paths:
  • Voluntary (recipient approves)
  • Arbiter-forced (third-party adjudication via ArbiterFund)
  • Early release (EIP-712 signature)
• Arbiter fund management — deposit liquidity, settle debts
• Decision guide — helps users choose the right refund path for their use case
• 6 antipatterns with fixes (zero refundTo, missing approve, insufficient arbiter funds, signature replay, wrong decimals, missing state checks)
• Complete code examples using Viem for all flows

Use Cases

• Merchant chargeback systems
• Gig economy milestone payments
• AI-validated service delivery
• Any scenario requiring reversible USDC payments with third-party arbitration

References

Based on:

• https://github.com/circlefin/refund-protocol
• Issue New skill proposal: use-refund-protocol #11

Testing

Skill follows existing patterns from bridge-stablecoin and use-agent-wallet. All code examples use standard Viem patterns consistent with other Circle skills.

Closes #11

[zkasuran]

Closing this one.

Three open PRs add the same file. #12 opened plugins/circle/skills/use-refund-protocol/SKILL.md on 9 April, seven weeks before mine, and #32 followed in June. One skill does not need three PRs and #12 was there first, so mine is the one to drop.

Two things for whoever triages the rest. The approving review on this PR is from an account with no write access here, so it never moved the merge state, which is still REVIEW_REQUIRED. And every skill under plugins/circle/skills/ on master arrived through circle-github-action-bot syncing from crcl-main/skills, so a PR against this copy is probably not the path a new skill takes.

#11 is still open. If any of the refund-protocol material here is useful (the three refund paths, arbiter fund deposits and debt settlement, the six antipatterns with fixes) it stays in the diff under Apache-2.0, so lift it into the internal copy freely.

[mistycornish11-stack]

Not his account
MistyCornish11@gmail.com 409)371-8223