077: Backend Contract Event Indexer

[bakarezainab]

#077: Backend Contract Event Indexer

Category: [BACKEND]
Difficulty: ● HARD
Tags: soroban, event-indexing, horizon, ledger, postgres

Description

Implement a background service in the Express backend that streams Soroban contract events from the Stellar RPC and persists them to PostgreSQL. Index events from bulk_payment, vesting_escrow, and revenue_split contracts so the frontend can query a reliable, queryable audit trail without hitting the RPC on every page load.

Acceptance Criteria

• Background worker polls or streams contract events from the Soroban RPC.
• Events stored in a contract_events table with contract_id, event_type, payload, and ledger sequence.
• REST endpoint GET /api/events/:contractId returns paginated events.
• Duplicate events idempotently skipped on re-indexing.
• Worker restarts gracefully from the last indexed ledger sequence on crash.