withX402() wraps the Web handler so unpaid calls get a standard HTTP 402
challenge (x402Version + accepts[]) and paid calls fall through to the agent.
Payment verification is injectable (host wires CoinPay/x402); CORS preflight
passes through untouched; custom challenge responses supported. README documents
the optional c0mpute.com GPU backend.
4 new tests; 38/38 pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
