Add Arc Testnet receipt watcher

[horn111]

Description

Adds the Arc Testnet receipt watcher for Arc Receipts.

This turns the receipts module from a manual recordPayment() flow into a local onchain payment ops flow:

• creates Memo-wrapped USDC payment requests for invoices
• uses official Arc Testnet USDC and Memo contract addresses
• watches Arc Testnet Memo events
• verifies the paired ERC-20 USDC Transfer
• creates receipts automatically when payment matches the invoice
• emits ledger events that can be signed as webhooks
• avoids double-counting native USDC system events
• adds duplicate transaction protection for repeated scans

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

N/A

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have added tests that prove my fix/feature works
• New and existing tests pass locally with my changes
• I have updated the documentation accordingly
• I have updated the CHANGELOG.md

Testing

npm.cmd run typecheck
npm.cmd run test --workspaces --if-present -- --reporter=dot
npm.cmd run build --workspace=packages/sdk

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Project	Deployment	Actions	Updated (UTC)
arc-nano-kit-demo	Ready	Preview, Comment	Jun 22, 2026 8:13pm