Add retrier interface and exponential backoff class.

[parthban-db]

🥞 Stacked PR

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• stack/api-execute-retrier [Files changed]
  • stack/update-agent-metadata-4 [Files changed]

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What changes are proposed in this pull request?

Add the api module with retry infrastructure, ported from the Go SDK's api/retrier.go. This is the first building block of the API execution layer.

• BackoffPolicy — exponential backoff with jitter, computing a random delay in [0, current] that grows by a configurable factor and is capped at a maximum. Based on the Exponential Backoff And Jitter pattern.
• Retrier — interface for retry decisions, returning a delay in milliseconds or undefined if the error is not retriable.
• retryOn — factory function that pairs a backoff policy with a custom predicate to produce a Retrier.
• BackoffPolicyOptions — exported configuration interface with JSDoc.

Notable deviations from Go:

• time.Duration → milliseconds as number.
• Retrier.isRetriable returns number | undefined instead of (Duration, bool) — idiomatic TypeScript.

How is this tested?

Unit tests.

[Divyansh-db]

Just a question, why have we not implemented RetryOnCode() as it exists in Go SDK?

[parthban-db]

Just a question, why have we not implemented RetryOnCode() as it exists in Go SDK?

Yeah, I will do that later. This PR doesn't complete the porting.