Per-Invoice Fuzz Test Suite

[Kingsman-99]

Description

Core arithmetic paths — split calculation, fee deduction, overflow guards — are only covered by hand-written unit tests. A dedicated fuzz test suite using cargo-fuzz should exercise these paths with randomised inputs to surface edge cases that unit tests miss.

Technical Context

Add fuzz targets in the fuzz/fuzz_targets/ directory: fuzz_split_calc.rs, fuzz_fee_deduct.rs, fuzz_ratio_validation.rs. Use libfuzzer_sys::fuzz_target! and import the calculation functions from contracts/split/src/lib.rs (extracted into a calc.rs module for testability). Update fuzz/Cargo.toml to list the new targets.

Acceptance Criteria

• Three fuzz targets exist covering split calc, fee deduction, and ratio validation
• Each target compiles under cargo fuzz build
• Running each target for 60 seconds finds no panics or overflows
• Corpus seeds covering boundary values (0, i128::MAX, i128::MIN) are committed to fuzz/corpus/
• fuzz/Cargo.toml lists all three targets under [[bin]]
• All CI checks (cargo build --target wasm32-unknown-unknown, cargo test, cargo clippy) pass and the branch has no merge conflicts

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[senmalong]

@senmalong has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

hi,

I’d love to take this issue on. I’m a smart contract and full-stack developer with experience across OnlyDust, Drips Waves 1–5, and the GrantFox beta campaign.

My stack includes Rust, Soroban, Cairo, Solidity, and TypeScript. I can deliver a clean, tested, and well-documented solution within 24 hours of assignment.

Happy to start immediately.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @senmalong to this issue.