feat(request): fund Tempo to Base through Relay contract deposits and Stargate (stack 7/8)

[brendanjryan]

Stacked on #279. Makes cross-chain funding work on Tempo mainnet. Before this, every bridged payment to Base failed with E_PAYMENT "No trusted cross-chain route can fund the payment", before any money moved.

Why it failed

On mainnet, Relay answers the CLI's strict deposit-address quote with HTTP 400: "strict is not supported for this origin chain". Without strict mode, it refuses exact output. The local e2e didn't catch this, because its stand-in relay mimicked the deposit-address API.

What changed

Relay contract-deposit mode. This is the MF-2 route in src/payment/upstream/relay-route.ts.

• The route accepts exactly two calls, and rejects any quote that adds, reorders, or changes them:
  • approve(source token → depository, amount);
  • depositErc20(wallet, token, amount, protocol.v2.orderId) on Relay's pinned v2 depository, 0x4cD00E387622C35bDDB9b4c962C136462338BC31. That address matches Relay's chains API.
• Both calls are re-encoded from the checked values and sent in one Tempo transaction.
• The deposit amount is bounded by the quote plus slippage.

Stargate route. This is MF-21, in src/payment/upstream/stargate-route.ts. It bridges USDC.e to native USDC.

• It sizes amountLD so the receipt covers the exact output, and sets minAmountLD to that output.
• It pays LayerZero's fee in LZD (approve, wrap, approve) and calls sendToken, all in one transaction.
• It tracks delivery through LayerZero Scan.
• Its fee counts toward amountIn, because machine-fetch ranks routes by amountIn alone (MF-22).

Source selection. Each payment funds from USDC.e (via Relay or Stargate, whichever is cheapest) or from OUSD (via Relay), depending on which one the wallet holds enough of. A resumed attempt always reconciles from the token it was submitted in. Recovery rebuilds the route by name.

UX fixes:

• --funding off with --payment-network base now pays from USDC already held on Base. Before, it silently paid the Tempo offer.
• A missing source balance is reported as E_INSUFFICIENT_FUNDS before any quote.
• When no route can fund a payment, the error now says why each route declined.

Mainnet, quote only

scripts/probe-funding-routes.mjs runs the real routes' quote() with execution disabled:

Source → Base USDC	$0.01	$1	$5
USDC.e via Relay	0.0313	1.0218	5.0238
USDC.e via Stargate	0.2684	1.2585	5.2589
OUSD via Relay	0.0363	1.0367	5.0787

Real Relay quotes pass the new validation, and Relay from USDC.e is the cheapest at about $0.022 flat. Stargate has a ~$0.258 flat LayerZero fee, so it only wins on large bridges.

Tests

• Unit tests: hostile-quote suites for both routes, with 23 contract-deposit cases and 20 Stargate cases. The full suite passes, 3,081 tests.
• e2e, 23 of 23 passing. It runs against a local depository and a local Stargate (test/e2e/contracts/LocalBridges.sol) plus stand-ins for Relay's API and LayerZero Scan. It covers:
  • Relay contract deposits and 10 hostile quotes;
  • Stargate selected when it quotes cheapest;
  • falling back to OUSD;
  • refusing before any quote when no source covers the payment;
  • kill-and-recover for both routes.

Upstream items found here: MF-21, MF-22, MF-23 (Relay errors drop the provider's reason), and MF-24 (multi-source crossChainFund).