Add poller retry and error handling

[pragmaticAweds]

Repository

This issue belongs in Fundable-Protocol/Backend under indexer/.

Migrated from Fundable-Protocol/stellar_indexer#12.

Context

Poller failures must not silently skip events or advance cursors after partial processing.

Scope

• Add retry policy for transient RPC errors
• Stop or surface clear errors for handler failures
• Ensure failed processing does not advance cursor
• Add tests for failure and retry behavior

Out of Scope

• Unrelated package work
• Docker, CI, or deployment work unless named in scope
• Broad refactors outside the touched package

Acceptance Criteria

• Scope items are complete
• Relevant tests are added or updated
• Documentation is updated when needed
• bun run type-check passes
• bun run test passes
• bun run lint passes
• bun run indexer:type-check passes
• bun run indexer:test passes
• bun run indexer:lint passes

Dependencies

• Implement event polling loop #29

Suggested Files or Packages

• indexer/common/src/poller/
• indexer/INDEXER_GUIDELINES.md

[olaayoade91-byte]

@olaayoade91-byte has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello please assign me this issue i can work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @olaayoade91-byte to this issue.

[ayomideadeniran]

@ayomideadeniran has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I'm a full-stack developer and I'd like to take this issue.
I understand the requirements and will follow the existing project structure, keep the implementation clean, and include proper tests where applicable.

ETA: 1–3 days (depending on scope)

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ayomideadeniran to this issue.

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Congratulations, @ayomideadeniran! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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[drips-wave]

This issue has been completed by @ayomideadeniran as part of the Stellar Wave Program's 6th Wave 🥳

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