feat: MoonPay fiat on-ramp with tracked buy rows and automatic Agglayer bridge to Miden

[0xnullifier]

What

Adds a fiat on-ramp (Buy) to the wallet: a MoonPay Buy widget embedded as a plain signed-URL iframe, purchases tracked as first-class buy activity rows, and the delivered token bridged automatically from the account's derived EVM address to the user's Miden account over Agglayer.

How it works

Widget (/buy) — src/lib/fiat-ramp/moonpay.ts builds the widget URL (sandbox buy-sandbox.moonpay.com for pk_test_ keys, prod otherwise) with the derived EVM address pre-filled; MoonPay requires HMAC-signing such URLs, so the signature comes from a local sign server (../moonpay-sign-server.mjs, holds the sk). No SDK, no remote script — MV3-safe.

Two extension-specific unblockers:

• credentialless on the iframe (extension pages run COEP require-corp; MoonPay sends no CORP header).
• A declarativeNetRequest session rule (moonpay-frame-rules.ts, installed at SW start) stripping MoonPay's frame-ancestors * CSP for extension-initiated MoonPay sub_frames only — per spec * never matches chrome-extension:// origins, so every extension is otherwise blocked regardless of dashboard allowlisting.

Purchase tracking — each /buy mount mints a session uuid (localStorage slot) carried as MoonPay's externalTransactionId. The app-root BuyBridgeManager (20s tick, outlives the /buy screen) polls the sign server's /tx-status proxy (sk-only endpoint); a completed purchase inserts a tracking-only BuyTransaction Dexie row (born Completed, extraInputs.bridgeProgress owns live state — same pattern as bridged-receive).

Auto-bridge — once the delivered token shows a balance on the derived address, the watcher gasses it via a local paymaster (../miden-paymaster, drips 0.0005 Sepolia ETH), then broadcasts approve + bridgeAsset on the lxly bridge (vault-signed via the restored lib/agglayer/vault-evm.ts, addressed to the Miden account via midenAddrToEvmAddr). Lifecycle: not-initiated → initiated → processed | failed, with delivery reconciled against the bridge indexer (reconcileBuyBridges, mirroring reconcileAgglayerBridgedReceives, wired into the AllHistory poll). The Agglayer note auto-consumes on arrival like any other.

UI — dedicated Activity row ("Buy / Via MoonPay → Miden", progress-driven status chip) and a HistoryDetails "Buy Details" card (route, bridged amount, Etherscan-linked EVM tx hash, error on failure) with live reload while non-terminal.

Misc — all vault-signed EVM paths moved off viem's default Sepolia RPC (thirdweb, 429s under light write traffic) to PublicNode.

Local pieces (not in this repo)

• ../moonpay-sign-server.mjs — URL signing + /tx-status proxy + webhook receiver (dev aid).
• ../miden-paymaster — minimal Sepolia gas drip server. Interim: the target architecture is EIP-7702 sponsorship (relayer pays gas, EOA delegates to a smart-account implementation); the drip unblocks the end-to-end flow now.

Testing

• Sandbox purchase end-to-end with pk_test_ keys (EUR→USDC, Banxa unavailable on the sandbox key per Onramper/MoonPay sandbox constraints; MoonPay test card).
• MoonPay sandbox never settles on-chain, so the bridge leg was exercised by planting the test ERC-20 (0x699cFE…4A17, Sepolia) on the derived address: paymaster drip → approve → bridgeAsset broadcast → indexer-confirmed processed.
• yarn lint, tsc --noEmit, and the chrome extension build are green.

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