1. Adapter seam map
Map BaseUsdcAdapter to the #1032 PaymentBackend interface: quote IDs, quote addresses, transfer detection, refund metadata, and conformance expectations.
HappyVertical SDK #1029 · Base USDC / x402 adapter
A fixed-scope path from payment backend interface to Base USDC adapter.
This packet is tailored to happyvertical/sdk#1029, immediately downstream of the open #1032 payments interface PR. It turns the issue into a maintainer-ready implementation map before anybody wires live RPC, hot-wallet sending, or x402 proof validation.
2. Mock-first verification
Separate unit tests from RPC integration: mocked USDC Transfer logs, deterministic address derivation fixtures, and a tiny opt-in public-RPC smoke gate.
3. x402 proof boundary
Define what the adapter should parse locally from X-Payment, what must be confirmed on-chain, and where replay/idempotency checks sit before settlement is trusted.
Why this is de-risked now
The prerequisite package/interface PR is already open in #1032. The latest follow-up replaced the fixed conformance expiry with a fresh rolling expiry, and the TypeScript source gate passed. That means #1029 can be scoped against a concrete interface instead of inventing the adapter contract from scratch.
This packet deliberately avoids live wallet movement. It does not request private keys, seed phrases, hot-wallet authority, RPC secrets, or a real USDC transfer. Live payment integration should stay behind a maintainer-controlled integration gate.
Deliverables
- One-page implementation decomposition for #1029, split into safe PRs.
- Acceptance-criteria matrix mapped to tests: conformance, watch path, x402 proof, HD derivation, refunds, and live-RPC opt-in smoke.
- TypeScript fixture plan for Base USDC logs and x402 payment headers.
- Risk notes for payTo/child-address isolation, replay protection, refund authority, and hot-wallet boundaries.
- README-ready setup notes for Base RPC, testnet/mainnet caveats, and no-secret CI defaults.
Relevant proof
HappyVertical #1032
Payments package interface skeleton, conformance helper, and review fix already opened. USDC payment hook PR
Balance/allowance/approval sequencing with tests, typecheck, build and lint. x402 SDK helper PR
Payment helper, typed errors, tests, typecheck and build through a workspace. Bazaar indexing readback
Existing x402 diagnostic packet for discovery/facilitator issues.
Payments package interface skeleton, conformance helper, and review fix already opened. USDC payment hook PR
Balance/allowance/approval sequencing with tests, typecheck, build and lint. x402 SDK helper PR
Payment helper, typed errors, tests, typecheck and build through a workspace. Bazaar indexing readback
Existing x402 diagnostic packet for discovery/facilitator issues.