Add registering-an-erc-8004-agent-on-base skill

[xam-dev-ux]

Closes #36

Summary

Adds registering-an-erc-8004-agent-on-base skill — a behavioral, phase-based registration flow for the ERC-8004 Identity Registry on Base Mainnet and Sepolia, following the same agent-behavioral pattern as registering-agent-base-dev.

Motivation

AI coding agents consistently produce wrong information about ERC-8004: stale contract addresses, treating the three registries as one contract, confusing agentId (an ERC-721 tokenId) with wallet addresses. A skill with the canonical addresses and a "you MUST load this skill" signal in the description fixes this at the routing layer before a wrong call gets made.

ERC-8004 is co-authored by Erik Reppel (Coinbase), Marco De Rossi (MetaMask), Davide Crapis (EF), and Jordan Ellis (Google). The Identity Registry is live on Base Mainnet with >256,000 agents registered. Contracts verified on-chain (version 2.0.0, "AgentIdentity" ERC-721) before opening this PR.

registering-agent-base-dev covers ERC-8021 (builder-code attribution) — a completely different standard. Zero overlap.

This was tested live on Base Sepolia before opening this PR

Full end-to-end flow executed against 0x8004A818BFB912233c491871b3d84c89A494BD9e:

• balanceOf pre-flight check → 0 (no prior registration)
• register() with no URI → agentId 6199 (from Registered event)
• Built registration file JSON with real agentId, encoded as data:application/json;base64,...
• setAgentURI(6199, dataURI) → confirmed on-chain
• ownerOf(6199), tokenURI(6199) (decoded JSON), getAgentWallet(6199) — all read back correctly
• balanceOf post-registration → 1

The EIP-712 typed data for setAgentWallet was verified against the contract source: AgentWalletSet(uint256 agentId, address newWallet, address owner, uint256 deadline) — the owner field is required and frequently missing from third-party documentation.

Scope

• Pre-flight check before registering
• Agent registration file schema (per ERC8004SPEC.md)
• IPFS / HTTPS / data-URI hosting
• register() overloads in viem + cast one-liners for both networks
• setAgentURI() for post-mint URI updates
• setAgentWallet() with correct EIP-712 typed data (EOA + ERC-1271)
• Read paths: ownerOf, tokenURI, getAgentWallet
• Key facts and out-of-scope notice

Out of scope

• Reputation Registry — reserved for a sibling skill
• Validation Registry — spec authors flag it as under active TEE community revision
• x402 payment integration

Checklist

• Scope approved in Proposal: add registering-an-erc-8004-agent-on-base skill #36
• Frontmatter and structure match existing skills; behavioral pattern follows registering-agent-base-dev
• Description optimised for skill triggering with "MUST load" signal
• Contract addresses verified on-chain and against erc-8004/erc-8004-contracts README
• Registration file schema verified against ERC8004SPEC.md
• EIP-712 type hash verified against contract source
• Full registration flow tested live on Base Sepolia (agentId 6199)
• README "Available Skills" table updated
• Single skill, single commit, no overlap with existing skills

[cb-heimdall]

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