refactor(contracts): internal M0 and Sherlock audit changes

[mesozoic-technology]

No description provided.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

✨ Finishing touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[toninorair]

I have doubts this is needed, getIndexRoundedDown should revert with DivisionByZero

[toninorair]

@mesozoic-technology https://github.com/m0-foundation/noble-dollar/blob/contracts/contracts/utils/IndexingMath.sol#L97

[mesozoic-technology]

If we were to revert, we'd be doing this on a cross chain message. In that case, what would happen to the yield the message intended to send? By returning instead, there is no ambiguity here, the yield is received by the contract, and the next time there is principal present to avoid a division by zero, the index is still updated to the correct value.

Maybe this would not be a problem given how Hyperlane works, but I chose this as I am not 100% familiar with that - would be good to know that, though.

[toninorair]

fair take, worth adding comment for auditors, just in case

[johnletey]

Thanks for your work on this @mesozoic-technology! Left two comments!