[API-515] feat: add SafeTransferLibTron for Tron USDT compatibility

[reednaa]

Summary

Tron USDT's transfer() returns false (32 bytes of zeros) on success. Solady's safeTransfer checks eq(mload(0x00), 1) and reverts — making USDT transfers through our escrow settler impossible on Tron. approve() and transferFrom() return true correctly, so the fix replaces safeTransfer with an approve-then-transferFrom pattern via a new Tron-scoped library. All existing chains are unaffected.

Linear: https://linear.app/lifi-linear/issue/API-515/handle-tron-usdt-broken-transfer-return-value-via-solady-transfer

Files touched

Ticket-named scope

• src/libs/SafeTransferLib.tron.sol

  • before: did not exist
  • after: SafeTransferLibTron library; safeTransfer checks self-allowance via inline assembly and calls safeApproveWithRetry + safeTransferFrom to bypass transfer()

• src/input/escrow/InputSettlerEscrowLIFI.tron.sol

  • before: did not exist
  • after: InputSettlerEscrowLIFITron extends InputSettlerEscrowLIFI; overrides _resolveLock() to use SafeTransferLibTron in place of Solady's safeTransfer at both the fee and destination transfer sites

• test/mocks/MockUSDT.tron.sol

  • before: did not exist
  • after: MockTronUSDT extends OIF's MockERC20; overrides transfer() to execute normally but return false

• test/libs/SafeTransferLib.tron.t.sol

  • before: did not exist
  • after: 9 unit tests covering normal token, Tron mock, fuzz, zero-amount, insufficient-balance revert, max-approval reuse, and a negative test confirming Solady's safeTransfer reverts with TransferFailed on the mock

• test/input/escrow/InputSettlerEscrowLIFI.tron.t.sol

  • before: did not exist
  • after: InputSettlerEscrowLIFITronTest extends OIF's InputSettlerEscrowTest (24 inherited tests pass with MockTronUSDT); adds fee-distribution and no-fee cases

Out-of-ticket-scope

• src/input/escrow/InputSettlerEscrowLIFI.sol — _domainName() made virtual

  • Note: required to allow InputSettlerEscrowLIFI.tron.sol to override and set a distinct EIP712 domain ("OIFEscrowLIFITron"), preventing cross-chain signature replay

• snapshots/inputSettler.json — gas snapshots updated

  • Note: auto-updated by forge test; new Tron test snapshots added

Out of scope (untouched, per ticket)

• Output settler — ticket explicitly excludes output settler changes for Tron
• InputSettlerCompactLIFI — ticket notes it "may need similar treatment if it ever does direct transfers on Tron"; it currently uses ERC6909 batchClaim, no direct ERC20 transfers
• Solady upstream — ticket explicitly excludes upstream PR

How it works

SafeTransferLibTron.safeTransfer avoids calling transfer() entirely. It reads self-allowance via a memory-safe assembly staticcall to allowance(self, self), approves type(uint256).max if needed (via safeApproveWithRetry, which handles the reset-to-zero pattern), then calls safeTransferFrom(self, to, amount). Both approve and transferFrom return true on Tron USDT, so all Solady checks pass.

How to validate

• forge build — clean
• forge test — 77/77 pass
• Manual: deploy InputSettlerEscrowLIFITron to Tron testnet, submit an order with USDT, confirm _resolveLock executes without revert

Risk & rollback

• Rollback plan: InputSettlerEscrowLIFITron is a new contract; existing deployments on all other chains use InputSettlerEscrowLIFI and are untouched. No rollback needed for non-Tron chains.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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