Wire IndexerModule into the app and implement the Soroban polling loop

[BigBen-7]

GistPin — GrantFox bounty issue. Reviewed against the acceptance criteria below. Read contracts/README.md first — it has the full ABI, event schema, and error codes for the deployed contract.

Context

GistPin's design intent (see Backend/README.md) is that the chain is the
source of truth — gists posted directly on-chain (e.g. by a future
wallet-direct frontend) must still show up via the API. That requires an
indexer that polls Soroban and reconciles into Postgres. The module exists
but is inert.

Problem

Backend/src/indexer/indexer.module.ts and indexer.service.ts exist but
IndexerModule is never imported into AppModule. It currently does
nothing when the app runs.

Scope

In scope:

• Import IndexerModule into AppModule so its poll loop actually runs.
• Implement/complete the poll loop: track the last-processed ledger
  (persist it — don't reprocess from genesis on every restart), fetch new
  events since that ledger via SorobanService.getEventsSince, and hand
  each decoded event off to a handler (the persistence logic is a separate
  issue — this issue is the polling/scheduling plumbing).
• Sensible polling interval (use @nestjs/schedule, already a dependency)
  and basic error handling (a single bad event/ledger must not permanently
  wedge the loop).

Out of scope: the actual DB writes for each event type (next issue) —
stub/log them here if that issue isn't merged yet, or coordinate order.

Acceptance Criteria

• IndexerModule runs as part of the app on startup
• The last-processed ledger is persisted (survives a restart — no
  reprocessing from scratch every time)
• A malformed/unexpected event does not crash the poll loop or stop
  subsequent ledgers from being processed
• Unit tests cover: normal polling advances the ledger cursor, and a bad
  event is skipped without halting the loop
• npm run build && npm test pass

How to verify your own work

cd Backend && npm run start:dev
# post a gist directly via the contract CLI (bypassing the API) and confirm
# the indexer's logs show it being picked up on the next poll
stellar contract invoke --id CCOVX5S3SYHVKUKM3NUXLH6COIYLV5BL3XD6HPFLLR4VLQEQGINJMDRV --source <your-identity> --network testnet --send=yes -- post_gist --location_cell "idxtest" --content_hash "QmIdx"

Depends on: the event-decoding issue.
Blocks: the "persist events to Postgres" issue.
Estimated effort: Medium (1-2 days). NestJS scheduling knowledge helpful.

[Preciousuche]

Hello PinSpace team,

I’d like to work on the “Wire IndexerModule into the app and implement the Soroban polling loop” issue.

I have experience building backend systems with TypeScript/Node.js and have been actively contributing to open-source projects, particularly those involving blockchain infrastructure and developer tooling. This issue aligns well with my interests in event-driven architectures and blockchain indexing.

My implementation plan is to:

Integrate the existing IndexerModule into the application’s startup lifecycle.
Implement a robust Soroban polling loop to continuously monitor and process on-chain events.
Ensure the polling process is resilient, avoiding duplicate processing while handling failures gracefully.
Follow the project’s existing architecture and coding conventions to keep the solution maintainable.
Add appropriate logging and error handling to improve observability and debugging.
Write comprehensive tests to validate the polling logic and integration.

My goal is to deliver a reliable, well-tested implementation that strengthens the application’s indexing infrastructure and provides a solid foundation for future event-processing features.

Thank you for considering my application. I look forward to contributing to PinSpace and collaborating with the team.

Best regards,

[kiel997]

I would like to take on this backend task. I will wire the IndexerModule into the application and implement a reliable Soroban polling loop for continuously fetching and processing new blockchain events. I will ensure the polling process is properly integrated with the application lifecycle, prevents duplicate event processing, handles RPC failures and retries gracefully, and maintains the correct polling state. I will also add appropriate unit and integration tests to verify module initialization, event polling, processing, error handling, and recovery.

[grantfox-oss]

🦊 GrantFox — @kiel997 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 #1035)
2. Your PR will be reviewed by the PinSpace-Org maintainers

Good luck! Track your progress on GrantFox.