Add cross-contract conservation test for vault + settlement + revenue_pool

[greatest0fallt1me]

Description

This is a smart-contract issue for the GrantFox campaign. End-to-end test that the sum of deposits across all three contracts equals total in vault.

Requirements and Context

• e2e test runner
• Random action sequence
• Invariant asserted
• CI runs nightly
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b task/cross-contract-invariant

2. Implement changes
   • contracts/tests/cross_contract_conservation.rs (new)
   • .github/workflows/e2e.yml
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

test: cross-contract conservation invariant

Acceptance Criteria

• Runner works
• Sequence randomized
• Invariant holds
• CI scheduled

Guidelines

• Minimum 95% test coverage with cargo test
• require_auth on every state-changing entrypoint
• Overflow-safe math; no unwrap() in production paths
• Clear NatSpec-style /// rustdoc
• Timeframe: 96 hours

[wavyboy-build]

@wavyboy-build has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello maintainer please assign to me

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

[drips-wave]

Congratulations, @wavyboy-build! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @wavyboy-build: 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.

Warning

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