Persist Stellar listener cursor in Postgres and add contract-event idempotency guard

[Copilot]

The Stellar event listener stored its cursor in Redis with a global 60s TTL, so restarts could lose cursor state and either skip unprocessed events or reprocess historical ones. This change makes cursor state durable and adds duplicate-suppression for contract-event job dispatch.

• Durable cursor persistence

  • Introduced EventCursor persistence in Postgres (event_cursors) and moved cursor load/save from cache to Prisma.
  • StellarEventService now reads/writes a stable cursor record keyed by stellar:event_listener:cursor.

• Startup cursor validation and safe roll-forward

  • On bootstrap, the saved cursor is validated against current STELLAR_HORIZON_URL and STELLAR_NETWORK_PASSPHRASE.
  • If cursor is missing, mismatched, or invalid, listener rolls forward to now and persists that state before streaming.

• Idempotent contract-event dispatch

  • Added ProcessedContractEvent table (processed_contract_events) with unique (txHash, eventType).
  • Before enqueueing process-event, service checks for existing processed key; duplicates are skipped.
  • Queue jobs are assigned deterministic jobId (${txHash}:${eventType}) to reduce duplicate enqueue pressure.

• Schema additions

  • Added Prisma models:
    • EventCursor (durable stream cursor + network metadata)
    • ProcessedContractEvent (dedupe key history)

await this.contractEventsQueue.add(process-event, payload, {
  jobId: `${payload.txHash}:${payload.eventType}`,
});

await this.prisma.processedContractEvent.create({
  data: {
    contractId: payload.contractId,
    eventType: payload.eventType,
    txHash: payload.txHash,
    pagingToken: payload.pagingToken,
  },
});

Closes OrbitChainLabs#13