Add Retry and Backoff to SDK Event Subscription

[Mosas2000]

Description

The SDK event subscription does not back off on failure. sdk/src/client.ts subscribeToEvents polls on a fixed interval (pollIntervalMs ?? 5000) and on error only calls onError before immediately retrying at the same cadence, with no exponential backoff or jitter. Repeated failures can hammer the RPC.

This is distinct from #677 (SDK workspaces/CI onboarding and typed wrappers), which addresses build integration, not subscription resilience.

Requirements and context

• Implement exponential backoff with jitter on polling failures
• Cap backoff at a configurable maximum
• Reset backoff after a successful poll
• Surface backoff state via the subscription options
• Add tests covering backoff progression and reset

Suggested execution

Fork the repo and create a branch

git checkout -b feature/sdk-event-backoff

Implement changes

• Add backoff/jitter to the event poll loop
• Add configuration for max backoff
• Add comprehensive tests

Example commit message

feat: add retry and backoff to SDK event subscription

Guidelines

• Assignment required before starting
• PR must include a closing reference to this issue
• Timeframe: 72 hours

[omosvico]

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

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