Fuzz differential test vs. a reference model of balances

[joelpeace48-cell]

Epic: Contract Safety & Hardening

Summary

Run operations against both the contract and a simple reference model, asserting they agree.

Background & Problem

Differential testing catches subtle logic divergences unit tests miss.

Acceptance Criteria

• Randomized op sequences agree with the model.
• Divergences fail CI.

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Filed as part of the mainnet-readiness & world-class roadmap. Scope is intentionally small enough for one focused PR; comment to claim.