fix(examples): wallet-bridge-smoke checks the wrong settlement header

[M0nsxx]

What's wrong

Ran examples/unity-game-x402-gate from scratch on my own machine (fresh clone, own testnet keypairs, own OpenZeppelin Channels testnet facilitator key) to independently verify it before a HackMeridian Lisboa demo. npm test passed (3/3, mocked). npm run wallet-bridge-smoke actually settled a real payment on Stellar testnet — server returned the unlocked loot — but printed:

[smoke] no settlement header found on the response — check facilitator/server logs for the settled tx hash.

even though the payment had gone through. Root cause: scripts/wallet-bridge-smoke.ts (lines 104-105) checks response.headers.get("x-payment-response") (x402 v1's header name) and response.headers.get("settlement-response") (not a real header in either version). Neither matches what @x402/express v2 actually sends.

Confirmed against the spec, not just my own run: specs/transports-v2/http.md, section "Settlement Response Delivery", states the server sends settlement results in a PAYMENT-RESPONSE header. That matches this example's own PAYMENT-SIGNATURE/PAYMENT-REQUIRED naming.

The fix

response.headers.get("payment-response") (header lookups are case-insensitive). One-line change, comment cites the spec section.

Two doc gaps found along the way

Both cost me real time on a from-scratch run, so I fixed them rather than filing separately:

1. .env.example and README.md say POST https://channels.openzeppelin.com/testnet/gen for the facilitator key. A POST there returns 401 Unauthorized; it's a GET.
2. The README only says to fund/trustline the player account. If X402_SELLER_ADDRESS is a freshly generated keypair (as opposed to pointing at an already-funded account), it also needs to exist on-chain and hold the USDC trustline before it can receive the SAC transfer — otherwise wallet-bridge-smoke fails simulation with HostError: Error(Contract, #13) / "trustline entry is missing for account". Added a note.

Evidence this was actually run, not just read

• Settled testnet tx (post-fix run, script correctly printed this): a7ed5747b475eb29127fde0e347860d3b66cce7accece3de830353b8a194f4ab — successful: true, ledger 4764067.
• Decoded payment-response header from that run:

  {"success":true,"payer":"GDCCBC35VPNQGDZE3O3GFZAIV6X7JE7HK7V7IJKQJSFOW5CFRCXF4DT5","transaction":"a7ed5747b475eb29127fde0e347860d3b66cce7accece3de830353b8a194f4ab","network":"stellar:testnet"}

• npm run typecheck and npm test both pass on this branch.

Test plan

• npm install
• npm run typecheck
• npm test (3/3 pass, mocked)
• npm run wallet-bridge-smoke against real Stellar testnet — settled, loot unlocked, tx hash printed correctly

🤖 Generated with Claude Code