docs: add unified agentic flow example combining X402, ERC-8004 and ERC-8183

[consumeobeydie]

Summary

This PR adds a unified agentic flow example that combines all three Arc Testnet standards in a single automated agent.

What's included

• Complete unified flow: X402 payments + ERC-8004 identity + ERC-8183 jobs
• Single agent wallet running all three protocols in sequence
• Live on-chain proof on Arc Testnet

Live Results

• Main Agent: 0x54b4B44749a95070560509B6Ec0be501665CcF63
• Agent ID: 69828 (ERC-8004)
• Job ID: 110935 (ERC-8183)
• Job Status: Completed
• Budget: 1 USDC

Complete PR Series

This PR completes the full agentic stack documentation:

1. docs/foundry-smart-contract-deploy-guide
2. docs/x402-arc-agent-example
3. docs/erc8004-agent-registration-example
4. docs/erc8183-job-lifecycle-example
5. docs/unified-agentic-flow-example (this PR)

Full repository: https://github.com/consumeobeydie/arc-agent-api

[osr21]

Cross-reference: Arc Stablecoin DApp implements all three (X402 + ERC-8183 + USYC)

The Arc Stablecoin DApp (live demo) implements the complete unified agentic stack you're documenting here. A few implementation notes that may be useful:

---

ERC-8183 AgenticCommerce

Deployed at 0x0Ecdad8fdA2Dde60E475e70Ebf177F2299FECB48. Key finding: createJob() requires 400k gas on Arc (not the default 200k). All other operations need 200k minimum. Arc's opcode pricing is higher than standard EVM — estimateGas returns unreliable values for these calls.

Gasless Transfer (EIP-3009)

Arc USDC does not support EIP-2612 permit(). Use transferWithAuthorization() (EIP-3009) instead. EIP-712 domain must use name: "USDC" and version: "2" — not "USD Coin". MetaMask also requires EIP712Domain to be explicitly present in the types object or the signature is silently corrupted. Full resolution in #164.

USYC Yield Vault

The Hashnote Teller returns custom error 0x7f63bd0f (NotEntitled()) for any non-allowlisted wallet. Testnet access requires a Circle Support ticket with your Arc wallet address. UI should gate the deposit button on isEntitled(address) to avoid on-chain reverts. See #183 for full details.

---

The dapp's full-stack source (React + Express + Solidity) may be useful as a reference alongside your documentation examples.