[Quality] Prove milestone totals and amount arithmetic cannot overflow

[1nonlypiece]

Problem

Milestone schedules and token amounts are financial inputs; unchecked sums or conversions can lock or misroute funds.

This issue requires a meaningful production implementation. Typo-only, documentation-only, formatting-only, dependency-only, or cosmetic changes do not satisfy the scope.

Objective

Add checked arithmetic and invariant tests for milestone totals, remaining balances, and release amounts.

Scope

Define precision policy, reject malformed schedules, and verify behavior at maximum representable values.

Acceptance criteria

• Milestone totals cannot exceed the vault amount.
• Every release preserves the remaining-balance invariant.
• Overflow and invalid precision are rejected without partial writes.
• Property or fuzz tests cover randomized schedules and extreme values.
• Existing CI/CD checks remain green.
• The PR explains the design, tradeoffs, test evidence, and any remaining limitations.
• The PR references this issue with Closes #{issue-number} or Fixes #{issue-number}.

Implementation notes

Implement only the stated behavior; keep unrelated refactors out of the PR.

Non-goals

• Do not remove tests merely to make CI pass.
• Do not introduce secrets, private keys, credentials, or mainnet-only values.
• Do not change unrelated APIs, UI surfaces, contract behavior, or deployment configuration.

Contributor application

Before starting, comment with relevant experience, a 1–4 bullet implementation approach, and an estimate for opening the first draft PR. Wait for maintainer assignment before coding. Only the assigned contributor is eligible for reward consideration.

Submission requirements

• Use PR title format [#<issue-number>] <short summary>.
• Check off each completed acceptance criterion.
• Include focused automated tests for success, failure, authorization, and boundary behavior where applicable.
• Include the validation commands and results in the PR description.
• Address maintainer review feedback before merge.

GrantFox reward consideration is based on the original scope, implementation quality, tests, security review, CI/CD results, review feedback, and follow-up stability; completion or merge alone is not a guarantee.

[rupesh-kumar-sah]

Hello @maintainers,

I would love to take this on. My planned approach:

• Implement [Quality] Prove milestone totals and amount arithmetic cannot overflow with explicit require_auth checks, clean storage layouts, and robust Soroban contract logic.
• Add comprehensive unit tests verifying both happy-path invocations and unauthorized revert scenarios.

Happy to pick this up today—please assign to me!

[Rodrigoue9]

Hi maintainers, I would like to tackle #420.

Relevant Experience

• Senior Rust/Soroban smart contract engineer with strong background in formal invariant proofs, checked arithmetic, and overflow security audits.

Proposed Approach

1. Milestone Arithmetic Hardening: Replace unchecked sums and divisions in milestone calculations with checked_add, checked_sub, and checked_mul returning typed ContractError::ArithmeticOverflow.
2. Invariant Proofs: Verify and enforce on-chain invariants: the sum of all milestone allocation amounts must strictly equal total project funding (sum(milestones) == total_amount).
3. Boundary Condition Tests: Add comprehensive unit tests and fuzzing harnesses asserting behavior under extreme i128::MAX boundary values and fractional zero-remainder checks.

Estimate: PR ready in 18h.

[guptakumarranjeet150]

Hello team,

I looked into [Quality] Prove milestone totals and amount arithmetic cannot overflow and have an implementation approach ready.

Proposed steps:

1. Audit storage layout and state invariants ensuring strict auth guards.
2. Implement deterministic state transitions with safe checked arithmetic.
3. Add hermetic unit and regression tests covering authorized, unauthorized, and boundary edge cases.
4. Profile instruction and CPU/gas limits under Soroban host environment.

I can deliver a clean, tested PR within 24 hours. Please assign!

[shobhamerabacha-star]

Hi,

I have experience with similar implementations and would like to take this on.

Proposed steps:

1. Audit storage layout and state invariants ensuring strict auth guards.
2. Implement deterministic state transitions with safe checked arithmetic.
3. Add hermetic unit and regression tests covering authorized, unauthorized, and boundary edge cases.
4. Profile instruction and CPU/gas limits under Soroban host environment.

Could you please assign this issue to me? Looking forward to delivering a clean PR.

[ranjeet150]

Hello team,

I looked into [Quality] Prove milestone totals and amount arithmetic cannot overflow and have an implementation approach ready.

Plan:

1. Audit storage layout and state invariants ensuring strict auth guards.
2. Implement deterministic state transitions with safe checked arithmetic.
3. Add hermetic unit and regression tests covering authorized, unauthorized, and boundary edge cases.
4. Profile instruction and CPU/gas limits under Soroban host environment.

I can deliver a clean, tested PR within 24 hours. Please assign!