Add AgentTax action provider

[AgentTax]

Summary

Adds AgentTaxActionProvider so AgentKit agents can handle US sales tax compliance end-to-end on Base. The new remit_tax_onchain action appends the AgentTax Base Builder Code (bc_626v2pr2) to USDC transfer calldata via ERC-8021 for attribution in the Base developer dashboard.

Why

Agent marketplaces, x402 micropayment services, and autonomous commerce platforms on Base have a shared unsolved problem: who collects and remits sales tax on these transactions? As agent-to-agent commerce grows, more of the AgentKit ecosystem is accepting USDC for digital goods and services — but none of it currently has a compliance layer.

AgentTax is a compliance API purpose-built for the agent economy (51-jurisdiction sales tax engine, ~43,000 zip-level local rates, IRS 1099-DA export, nexus monitoring). This action provider lets any AgentKit agent use it natively.

Actions

Action	Auth	Onchain
calculate_tax	Optional	No
get_local_rate	Optional	No
check_nexus_status	Optional (demo mode without)	No
export_1099_da	Optional (demo mode without)	No
remit_tax_onchain	Optional (audit log if set)	Yes — Base

Public actions work without an API key. Authenticated actions fall back to AgentTax demo data without a key and return real data for the configured entity when a key is provided.

Base Builder Code integration

The remit_tax_onchain action appends the ERC-8021 suffix

0x62635f36323676327072320b0080218021802180218021802180218021

to the USDC transfer calldata. Decoded: bc_626v2pr2 (ASCII) + length byte (0x0b) + 8021 magic pattern. Gas overhead is ~450 gas per transaction (16 gas per non-zero byte). Smart contracts ignore the trailing bytes, so the transfer behaves normally.

Attribution can be opted out via builderCodeEnabled: false in the provider config. Registered via https://dashboard.base.org.

Testing

• 37 unit tests, all passing
  • Schema validation including the real transaction_type enum, state code normalization, ZIP format, required counterparty_id
  • ERC-8021 Builder Code encoding round-trip test (decodes [ascii code][length byte][magic pattern])
  • All 5 actions: happy path, HTTP error, success: false body handling, and network failure paths
  • remit_tax_onchain assertions: USDC transfer selector, correct per-network USDC address, Builder Code suffix presence, opt-out behavior, audit log on/off, recipient validation, non-Base network rejection
  • supportsNetwork across EVM/non-EVM
• Full suite: 901 / 901 passing (no regressions)
• E2E smoke tested against the live AgentTax API — verified request body shape matches the /api/v1/calculate contract and response parses cleanly
• Type-check, ESLint, and Prettier all clean

Usage

import { AgentKit, agentTaxActionProvider } from "@coinbase/agentkit";

const agentKit = await AgentKit.from({
  walletProvider,
  actionProviders: [
    agentTaxActionProvider({
      apiKey: process.env.AGENTTAX_API_KEY,    // optional
      reserveWallet: "0xYourTreasuryWallet",   // default recipient for remit
    }),
  ],
});

// Typical agent flow:
// 1. calculate_tax        - determine collection amount
// 2. collect payment      - via erc20 / x402 / your payment flow
// 3. remit_tax_onchain    - transfer collected tax (Builder Code attached)

Full README with per-action docs: typescript/agentkit/src/action-providers/agenttax/README.md

Links

• AgentTax: https://agenttax.io
• Base Builder Codes: https://docs.base.org/base-chain/builder-codes/builder-codes
• ERC-8021: https://eips.ethereum.org/EIPS/eip-8021

Checklist

• Provider added under typescript/agentkit/src/action-providers/agenttax/
• Registered export in src/action-providers/index.ts
• Added .changeset/add-agenttax-action-provider.md
• Added README with usage examples
• 37 unit tests cover all actions, schemas, and Builder Code encoding
• Full suite passes (901 / 901)
• Type-check passes
• ESLint + Prettier clean
• E2E smoke tested against live AgentTax API

[cb-heimdall]

🟡 Heimdall Review Status

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