[Kewe63]

Summary

• Rejects zero and EOA/no-code FiatToken targets when deploying FiatTokenUtil.
• Adds focused constructor regression coverage for invalid and deployed-code targets.
• Fixes FiatTokenUtil can report successful transfers when configured with a no-code target #685.

Detail

transferWithMultipleAuthorizations uses a low-level call and treats the EVM success bit as a successful transfer. Calls to addresses without deployed code return success with empty data, so a utility configured with such a target can report successful transfers without executing FiatToken logic.

The constructor now uses OpenZeppelin's Address.isContract to require that the immutable target already has deployed code. Correctly configured instances retain the same runtime behavior; the change only rejects invalid deployments earlier.

Because isContract relies on deployed bytecode, the target must already be deployed when constructing FiatTokenUtil. Existing proxy-based deployments satisfy this requirement.

Testing

• Confirmed the new invalid-target tests fail against the previous constructor behavior.
• yarn compile
• yarn static-check
• yarn hardhat test test/v2/FiatTokenUtil.test.ts --no-compile — 3 passing
• forge test -vvv — 8 passing
• Full Hardhat CI matrix — a local broad-group attempt was OOM-killed under a 3.7 GiB WSL environment; the focused regression suite and repository compile/static checks pass.

Documentation

Issue #685 was updated with the repository-native regression test path. No user-facing documentation changes are required.

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Requested Reviewers: Maintainers