Add comprehensive contract integration tests for Soroban-backend interaction

[Wilfred007]

What

No tests verify the interaction between Soroban contracts and the backend event indexer. Add integration tests that deploy contracts, execute operations, and verify backend indexes events correctly.

Why

Contract events and backend indexing are separate systems that must work together. Currently tested in isolation.

Scope

In scope: Deploy contracts to local Soroban, execute operations, verify events indexed, verify API returns data
Out of scope: Testnet testing

Acceptance Criteria

• Tests deploy each contract to local Soroban
• Execute bulk payment, verify events indexed
• Execute vesting, verify events indexed
• API returns contract event data

Technical Context

• contracts/ — Soroban contracts
• backend/src/services/contractEventIndexerService.ts — indexer
• backend/src/__tests__/ — test directory

[Dev-journals]

Hi Maintainer. Kindly assign this issue to me. I have years of full-stack and blockchain development experience with deep expertise in Soroban contract deployment, event indexing, integration testing, and building end-to-end test suites that verify contract-backend interaction for production-grade applications.

My approach to this implementation:
Set up a local Soroban test environment using the stellar/quickstart Docker image or local node, with scripts to deploy contracts from the contracts/ directory and capture their deployed addresses for use in integration tests

Write integration tests that deploy each contract (bulk payment contract, vesting contract, etc.) to the local Soroban network, execute key operations (bulk payouts, vesting schedules, claims), and verify events are emitted correctly

After contract operations, test the backend indexer by triggering the contractEventIndexerService to process emitted events, then verify the data is correctly stored in the database and exposed via the API endpoints—ensuring indexer configuration (event parsing, contract address mapping, block range handling) works correctly

Test edge cases: contracts with multiple events, large batches of transactions, reorg scenarios (where applicable), and verify that the indexer handles them without data loss or duplication

Write comprehensive assertions: event data matches contract operation parameters, timestamps are correct, event order is preserved, and API endpoints return the indexed data in the expected format

Add setup/teardown helpers to clean the database and contract state between tests, ensuring tests are isolated and repeatable, and add a test runner script that automates the entire flow (contract deployment → operations → indexer processing → API verification). I am ready to deliver this comprehensive integration test suite with full test coverage across all contract types and robust CI integration.

[grantfox-oss]

🦊 GrantFox — @Dev-journals has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #559)
2. Your PR will be reviewed by the Protocol-Guild maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Third Campaign campaign!

@Dev-journals's PR #604 was approved and merged by @Wilfred007.

🏆 @Dev-journals: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (411 total points). Track your full progress on GrantFox.

👏 Great work, @Dev-journals! Keep contributing to Protocol-Guild.