v0.4.0 — x402 Payment Support

What's New

x402 (HTTP 402 Payment Required) support

Handle paywalled APIs in 4 lines:

const response = await fetch('https://api.example.com/data');
if (response.status === 402) {
  const result = await axon.x402.handlePaymentRequired(response.headers);
  const data = await fetch(url, {
    headers: { 'PAYMENT-SIGNATURE': result.paymentSignature },
  });
}

• client.x402.handlePaymentRequired(headers) — full flow: parse header → fund bot EOA from vault → sign EIP-3009 (USDC) or Permit2 (any ERC-20) → return PAYMENT-SIGNATURE header
• client.x402.fund(amount, token?) — fund bot EOA from vault for manual x402 flows
• EIP-3009 signing (src/eip3009.ts) — USDC-specific gasless transfer authorization
• Permit2 signing (src/permit2.ts) — universal ERC-20 via Uniswap Permit2
• x402 header parsing, chain matching, metadata extraction (src/x402.ts)
• Full Axon pipeline applies to x402 payments (spending limits, AI scan, human review)

Other changes

• relayerUrl config option — override the relayer URL for dev/testing
• x402Funding flag on PayInput — audit/context flag for x402 self-payments

Previous versions

• 0.3.7: Fix Arbitrum Sepolia WETH address
• 0.3.6: Fix Arb Sepolia WETH address (was using mainnet)
• 0.3.5: Add relayerUrl to AxonClientConfig
• 0.3.0: Add swap(), execute(), token resolution, amount parsing
• 0.2.0: Add getBalance(), poll(), vault read helpers
• 0.1.0: Initial release — pay(), EIP-712 signing, keystore support