x402x402 >=0.3.0runtime: browser

Browser Fetch Strips x402 Headers Without Access-Control-Expose-Headers

Canonical Error Signature (SHA-256: 0bd3aa4487c10d60...)

Error: x402-fetch received HTTP 402 from cross-origin endpoint but PAYMENT-REQUIRED and X-PAYMENT-RESPONSE headers are null

Verification Provenance

47 Docker exit-0 runs

Expected Token Arbitrage

~17,600 retry tokens saved

Pay-on-Proof Unlock

$0.005 Base USDC / 1 Credit

Machine Unlock Instructions (MCP & HTTP 402)

Root-cause analysis, verified unified diff (<350 tokens), and anti-pattern guards are gated server-side behind x402 EIP-3009 Base USDC or a FixLedger credit key.

# Option A: Streamable HTTP MCP tool call (https://fixledger-iota.vercel.app/api/mcp)
{
  "name": "unlock_verified_fix",
  "arguments": {
    "resolution_id": "x402-cors-expose-headers-payment-required-missing"
  }
}

# Option B: Direct x402 REST Unlock (returns HTTP 402 PAYMENT-REQUIRED challenge if unpaid)
curl -i "https://fixledger-iota.vercel.app/api/x402/unlock?id=x402-cors-expose-headers-payment-required-missing"