Test/vault batch deduct dup request id property

[blockchainrafik]

Closes #437

---

test(vault): Add property test for duplicate request_id handling in batch_deduct

This PR adds deterministic property-based test coverage to ensure the vault contract rejects duplicate request_id values within a single batch_deduct call atomically.

What's included

• test_idempotency.rs

  • Added a seeded PRNG helper for deterministic test generation.
  • Added build_duplicate_batch helper.
  • Added batch_deduct_duplicate_request_id_within_batch_rejected_atomically.
  • Verifies that duplicate request_id values within the same batch cause the entire operation to be rejected atomically.
  • Confirms meta.balance remains unchanged after rejection.
  • Verifies the duplicate request_id is not marked as processed.

• INVARIANTS.md

  • Documented the invariant that duplicate request_id values within a batch are rejected atomically without modifying the vault balance.

Purpose

Provide deterministic property-based test coverage for intra-batch duplicate request_id handling while documenting the expected vault invariant to prevent regressions.

Closes: #437

[drips-wave]

@blockchainrafik Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[greatest0fallt1me]

nice work — “Test/vault batch deduct dup request id property”. merged onto current main 🙏