OneLink Pay

Give your AI a card, not your wallet. OneLink Pay is a permission firewall for Universal Accounts: sign one scoped mandate, and an app, script, or AI agent can spend USDC only inside the per-charge, daily, and total caps you set — to a single merchant, until it expires, revocable anytime. Invalid charges are caught against the live on-chain policy during preflight simulation, before broadcast, so no funds move and no gas is spent. Completed checkout payments produce a public, verifiable proof receipt; agent charges expose their on-chain evidence.

Particle makes execution chain-abstracted; OneLink makes consent visible, limits enforceable, and every settlement provable.

Built for the UXmaxx Hackathon (Encode Club + 7702 Collective).

Watch the 3-minute demo · Open the live app · View the interactive pitch · Download the judge deck

Evaluate in 2 minutes (for judges)

Live app: https://onelink-pay.vercel.app

No login or wallet needed — verify the core claims right now:

1. Trigger the on-chain block yourself — no wallet, no gas → /try: one tap simulates the charge against the live Arbitrum SpendPolicy; an over-cap request returns PerChargeExceeded before broadcast, with no funds moved. The firewall, driven by you.
2. Verify the cross-chain payment (~60s) → open the live receipt /receipt/fc5adc83…; every tx is on arbiscan/basescan (settled on Arbitrum, USDC sourced from Base, InvoicePaid on Base). Full evidence: docs/proof-pack.md.
3. Replay the winning use case → /demo-replay: inspect how Particle funded the card from Base to Arbitrum, then see 0.13 USDC of useful inputs, an unexpected 0.20 USDC request blocked, and the on-chain revoke — with real explorer evidence and no wallet.
4. What's real vs pattern vs future is stated plainly in-app at /trust.

Explore the live product (the live buttons run on our funded demo account — we can drive it on stage):

• Research Agent Expense Card → /agent: arm a 0.10 USDC/tool budget → Run task with my budget → the deterministic workflow buys two paid inputs, produces an ETH market-risk brief, blocks an unexpected 0.20 USDC export before settlement, then lets the user revoke the budget on-chain.
• Cross-chain checkout proof → verified receipt: a merchant was paid on Arbitrum with USDC sourced from Base (no manual bridge), with Base, Arbitrum, and Particle activity evidence.

Prize fit: Particle Universal Accounts + EIP-7702 (cross-chain, chain-abstracted UX) · Magic (walletless Google/email login) · Arbitrum (USDC settlement + on-chain mandate enforcement).

Full talk track, judging-criteria map, and dry-run checklist: docs/demo-runbook.md.

What's live

• Permission Firewall — SpendPolicy.sol enforces an EIP-712 PaymentMandate (per-charge / daily / total caps + expiry + single-merchant + revoke). Deployed on Base (0x73C8…3957) and Arbitrum One (0x9782…164E). Over-cap charges revert with PerChargeExceeded — caught in simulation before broadcast, so no funds move and zero gas is spent. 22 Hardhat tests pass. Source verified on-chain — read the enforcement contract on Basescan and Arbiscan.
• Cross-chain settlement via Particle Universal Account (EIP-7702) — a Magic-signed UA pays a merchant on Arbitrum with USDC sourced cross-chain from Base in one operation — no manual bridge. Proven live (Arbitrum settle 0x85d8…4911, Base source 0x8b85…4a2e, UniversalX 0x0654e81cfea86a) and wired into /pay (NEXT_PUBLIC_PAYMENT_MODE=universal_7702_transfer, live in prod). Same-chain checkout runs on the same path.
• Research Agent Expense Card (x402-pattern) — /agent runs the real HTTP payment handshake (GET → 402 → pay → retry-with-proof → 200) through the on-chain mandate. In the verified run it bought market insight for 0.05 USDC and sentiment for 0.08 USDC, produced a readable brief, and refused an unexpected 0.20 USDC premium export because it exceeded the signed 0.10 USDC/tool cap. The workflow is deterministic, the payment and block are real, and the settlement scheme is onelink-mandate (not the Coinbase facilitator).
• UA-funded Expense Card (feature-gated, live-verified) — NEXT_PUBLIC_ENABLE_UA_FUNDED_AGENT=true connects /agent consent to Particle UA funding. On 2026-07-13, one completed Particle operation used a successful Base source leg to make the 2 USDC daily budget available on Arbitrum and approve the exact amount to SpendPolicy. OneLink waited for FINISHED, verified every reported operation receipt plus Arbitrum balance and allowance server-side, then stored immutable evidence before arming. Inspect the Particle activity. The repository default remains false as a rollback; the stable production demo has the verified path enabled.
• Legible consent — a plain-English mandate card before signing (EIP-712 hash behind a disclosure) and a live budget HUD that drains from on-chain SpendPolicy state.
• Proof receipts — ReceiptEmitter.sol emits an InvoicePaid event after server-side verification of the on-chain USDC Transfer. Public, shareable receipt at /receipt/[id] (copy-link + QR) with a "Cross-chain: Base → Arbitrum" badge and a UniversalX activity link. Deployed on Base (0x89CF…5bC3) and Arbitrum One (0xe4C6…D2A1).
• Walletless onboarding — Magic embedded wallet, email + Google OAuth (live, with auto-detect on reload).
• EIP-7702 delegation — Magic EOA delegated in-place via Particle UA (useEIP7702: true), proven on Base (tx 0x4ca6…cef0).

Honest scope

• ✅ The on-chain firewall is live and tested (22 Hardhat tests pass).
• ✅ Same-chain USDC checkout is proven end-to-end on Arbitrum, with proof anchored on Base.
• ✅ Cross-chain value movement via the Universal Account is proven live on @particle-network/universal-account-sdk@2.0.3 (stable): a merchant is paid on Arbitrum with USDC sourced cross-chain from Base in one operation. The active /pay rail is createUniversalTransaction + usePrimaryTokens:[USDC] + per-chain pre-delegation to the V2 7702 delegate; NEXT_PUBLIC_PAYMENT_MODE=universal_7702_transfer is live in prod.
• ✅ The integrated Research Agent card funding is proven live (C27): its 2 USDC Arbitrum budget was assembled through a completed Particle activity with a Base source leg, exact Arbitrum SpendPolicy approval, and fail-closed server verification before arming. The later 0.05 + 0.08 USDC resource purchases are separately proven same-chain Arbitrum settlements.
• ✅ Zero-native-gas delegation is proven live on Arbitrum: the one-time EIP-7702 delegation is relayer-sponsored (C23). This is scoped to that delegation step only (no general settlement paymaster; the Particle settlement fee is paid in USDC). Particle AuthKit is not installed or used; Magic is the live wallet and signer.

Honesty caveats:

• Both cross-chain value legs are independently inspectable on-chain and linked by the completed Particle activity; the flow was re-run through prod /pay on stable 2.0.3. The zero-native-gas delegation proof is scoped to the live Arbitrum C23 run.
• Prod runs the pinned stable Particle SDK (2.0.3) — real EIP-7702 + cross-chain, with same-chain and cross-chain settlement live-verified on it (RPC-checked, 2026-07-04).
• /agent uses the x402 pattern with a custom onelink-mandate settlement scheme — not the Coinbase EIP-3009 facilitator. The on-chain enforcement is real; the "agent" runs a real unattended deterministic loop over the same firewall (one click, then no human per-step) — not an LLM that reasons, so no AI decision-making is claimed.
• Particle AuthKit is not installed and is not part of the live path. Magic is the embedded wallet and signer used by the demo.

How OneLink compares (prior art)

Scoped spend permissions are not new — OneLink builds on the wave rather than reinventing it. The wedge is the packaging: an on-chain, revocable mandate bound to the x402 agent-payment rail, entered through a Particle Universal Account + EIP-7702, with a public proof receipt.

Prior art	What it is	Where OneLink differs
Coinbase / Base Spend Permissions	Allowance (token, period, amount) + revoke for smart wallets	Wallet-agnostic — the mandate is signed by the user's 7702 EOA and enforced by our auditable SpendPolicy; adds a public proof receipt + x402 binding
ERC-7715 / ERC-7710	Emerging standard: wallet-granted scoped permissions + delegation	A focused, auditable payments-specific mandate aligned to that vocabulary, shipping today
ZeroDev session keys	Low-level account-layer delegation (rate limits, allowed calls)	We enforce a payment policy (per-charge / daily / total / merchant) with legible consent + on-chain proof
Google AP2	Agent "mandates" as off-chain Verifiable Credentials	Same word "mandate", but enforced on-chain at the user's account — a promise becomes a guarantee
x402 (Coinbase)	HTTP 402 pay-per-call rail for agents; no spend controls	OneLink is the spending-limit layer that bounds x402 spend

The wedge: OneLink Pay is the on-chain, revocable spending limit for the x402 agent economy — built on Particle Universal Accounts + EIP-7702, with a public proof receipt for every payment.

Built with Particle (Universal Accounts + EIP-7702), Magic (email/Google embedded wallet), and Arbitrum (settlement).

Security Notes

POST /api/payment-links registers invoices on-chain from the server-side ReceiptEmitter owner wallet. To avoid public gas-drain, it requires:

x-admin-create-token: <ADMIN_CREATE_TOKEN>

POST /api/payments/[id]/mark-paid does not trust a frontend tx hash by itself. It fetches the settlement-chain receipt (Base or Arbitrum, per the invoice), parses the USDC Transfer, verifies merchant and amount, then records InvoicePaid through the ReceiptEmitter owner key — using the actual on-chain sender as the payer, never a client-supplied address — before marking Supabase as paid.

POST /api/mandates/charge is public but gas-safe: funds are bounded by the EIP-712 mandate signature plus the on-chain caps, and the relayer is protected by an optional dedicated RELAYER_PRIVATE_KEY and a rolling-window budget on gas-spending sends. Over-cap charges are caught in simulation and cost zero gas.

Required Env

NEXT_PUBLIC_APP_URL=http://localhost:3000
NEXT_PUBLIC_PARTICLE_PROJECT_ID=
NEXT_PUBLIC_PARTICLE_CLIENT_KEY=
NEXT_PUBLIC_PARTICLE_APP_ID=
NEXT_PUBLIC_MAGIC_PUBLISHABLE_KEY=
NEXT_PUBLIC_SUPABASE_URL=
NEXT_PUBLIC_SUPABASE_ANON_KEY=
SUPABASE_SERVICE_ROLE_KEY=
NEXT_PUBLIC_DESTINATION_CHAIN_ID=8453
NEXT_PUBLIC_PAYMENT_MODE=universal_7702_transfer
NEXT_PUBLIC_RECEIPT_EMITTER_ADDRESS=
# Permission Firewall (SpendPolicy) — REQUIRED for /firewall + /agent
NEXT_PUBLIC_SPEND_POLICY_ADDRESS=
NEXT_PUBLIC_SPEND_POLICY_ADDRESS_ARBITRUM=
BASE_MAINNET_RPC_URL=
NEXT_PUBLIC_BASE_RPC_URL=https://mainnet.base.org
NEXT_PUBLIC_ARBITRUM_CHAIN_ID=42161
NEXT_PUBLIC_ARBITRUM_USDC_ADDRESS=0xaf88d065e77c8cC2239327C5EDb3A432268e5831
ARBITRUM_MAINNET_RPC_URL=
NEXT_PUBLIC_ARBITRUM_RECEIPT_EMITTER_ADDRESS=
RECEIPT_EMITTER_OWNER_PRIVATE_KEY=
RELAYER_PRIVATE_KEY=
ADMIN_CREATE_TOKEN=
# "true" = relayer pays the one-time 7702 delegation (zero-gas onboarding, C23)
NEXT_PUBLIC_SPONSORED_DELEGATION=false
# Default-off until the integrated Particle funding send is live-verified
NEXT_PUBLIC_ENABLE_UA_FUNDED_AGENT=false
NEXT_PUBLIC_ENABLE_DEBUG_PROBES=false

The values above are safe local defaults (Base + universal_7702_transfer); the live prod demo is Arbitrum-first — set NEXT_PUBLIC_DESTINATION_CHAIN_ID=42161 to mirror it. NEXT_PUBLIC_SPEND_POLICY_ADDRESS* must be set for the firewall/agent demos. Never commit .env.local, private keys, seed phrases, or admin tokens. RELAYER_PRIVATE_KEY is optional (falls back to the ReceiptEmitter owner key). Keep NEXT_PUBLIC_ENABLE_DEBUG_PROBES=false in any deployed build — it gates the /debug/* lab routes and is inlined at build time.

Local Commands

corepack pnpm install
corepack pnpm dev
corepack pnpm typecheck
corepack pnpm lint
corepack pnpm test:unit          # 297 unit checks (node:test)
corepack pnpm build
cd contracts && corepack pnpm test   # 22 Hardhat contract tests

Deploy ReceiptEmitter v1.1 to Base mainnet:

cd contracts
BASE_MAINNET_RPC_URL=... RECEIPT_EMITTER_OWNER_PRIVATE_KEY=... corepack pnpm hardhat run scripts/deploy.ts --network base

SDK Versions

Pinned to what's installed (verified against the lockfile). The Universal Account SDK is on the pinned stable release (2.0.3) — real EIP-7702 + cross-chain; the other crypto SDKs are on their latest releases.

• @particle-network/universal-account-sdk: 2.0.3 (pinned exact; stable — real EIP-7702 + cross-chain)
• @particle-network/chains: 1.8.3 (latest)
• magic-sdk: 33.7.1 (pinned; latest 33.9.0, upgrade deferred until after submission)
• @magic-ext/evm: 1.5.1 (latest)
• @magic-ext/oauth2: 15.8.0 (latest) — Google OAuth
• viem: 2.53.1
• ethers: 6.17.0
• next: 14.2.35
• @openzeppelin/contracts: 5.6.1 (latest)
• hardhat: 2.28.6

Intentionally held back (major upgrades require code changes; out of scope mid-hackathon): next 14 → 16, zod 3 → 4, hardhat 2 → 3.

SDK note: prod runs the pinned stable Particle SDK (2.0.3) for real EIP-7702 + cross-chain. The earlier -32801/-32613 maintenance errors on custom universal calls are resolved (cross-chain payment proven live on stable); the version is pinned exact, so prod cannot float to a new release unreviewed.