[#479] Add Builder Code (ERC-8021) attribution

[realproject7]

Summary

• Creates lib/builder-code.ts — generates ERC-8021 DATA_SUFFIX from NEXT_PUBLIC_BUILDER_CODE env var using ox/erc8021 Attribution
• Updates lib/wagmi.ts — applies dataSuffix at wagmi config level so all transactions automatically include builder code attribution
• NEXT_PUBLIC_BUILDER_CODE left empty until operator registers at base.dev
• Uses EIP-5792 dataSuffix capability (NOT manual calldata append) per issue spec

Fixes #479

Operator items

• Register at base.dev to get builder code (e.g., bc_xxxxxxxx)
• Set NEXT_PUBLIC_BUILDER_CODE in Vercel env vars
• Verify attribution via Base Attribution Checker after first tx

Test plan

• Build passes (next build)
• With empty NEXT_PUBLIC_BUILDER_CODE: no dataSuffix applied, transactions work normally
• With valid builder code: dataSuffix appended to all transactions
• Verify via Attribution Checker that builder code is detected

🤖 Generated with Claude Code

[vercel]

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
plotlink	Ignored		Mar 24, 2026 9:25am

[project7-interns]

LGTM. Uses ox/erc8021 Attribution.toDataSuffix (EIP-5792 compliant), matches reference dropcast implementation. Gracefully disabled when NEXT_PUBLIC_BUILDER_CODE is empty. One note: dataSuffix at the wagmi createConfig level relies on the rest-spread being passed through to viem clients — this matches the reference impl so approve as-is, but worth a manual smoke test once the builder code is registered.

[project7-interns]

Verdict: APPROVE

Summary

The builder-code helper is minimal and the wagmi config wiring applies the suffix at the client level, which is the right place to cover all writeContract transaction paths without manual calldata manipulation.

Findings

• None.

Decision

Approve because the change is focused, uses the intended dataSuffix mechanism, and keeps attribution disabled cleanly until the operator provides a builder code.