Add property-based tests for DistributionEngine rounding invariants

[thlpkee20-wq]

Description

DistributionEngine.distributeWithBatch guarantees the sum of payouts equals revenueAmount to the cent via a max-share adjustment, but this invariant is only spot-checked. Add fast-check property tests (the repo already depends on fast-check) asserting the invariant holds across randomized balances, investor counts, and revenue amounts.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/services/distributionEngine.ts, src/services/distributionEngine.test.ts
• Property: sum(payouts) === revenueAmount and every payout >= 0

Suggested execution

• Fork the repo and create a branch
• git checkout -b test/distribution-rounding-property
• Implement changes
  • Add fast-check arbitraries for balance arrays and revenue amounts
  • Assert payout sum equals revenue and no negative payouts
  • Assert idempotent resume produces identical totals
• Validate security and correctness assumptions

Test and commit

• Run tests
  • npm test
• Cover edge cases
  • Single investor, zero-balance investors filtered, dust remainder of 0.01, large counts
• Include test output and notes

Example commit message

test: property-based rounding invariants for DistributionEngine

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

[Ayilojay]

@Ayilojay has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi Maintainer! I will like to work on this issue

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

[drips-wave]

Congratulations, @Ayilojay! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Ayilojay: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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