fix(util-retry): detect throttling from RetryErrorInfo.errorType in DefaultRateLimiter

[TrevorBurnham]

Issue #, if available:

Fixes #1328

Description of changes:

DefaultRateLimiter.updateClientSendingRate() calls isThrottlingError(response) to decide whether to enable client-side throttling. However, the AdaptiveRetryStrategy in @smithy/util-retry passes a RetryErrorInfo object — not an SdkError. Since RetryErrorInfo has none of the properties isThrottlingError checks ($metadata, $retryable, name), the call always returns false and the rate limiter is never enabled, completely defeating adaptive retry.

The fix adds a private isThrottlingResponse() method that checks for RetryErrorInfo.errorType === "THROTTLING" first, and falls back to isThrottlingError() when errorType is absent. This preserves backward compatibility with the deprecated AdaptiveRetryStrategy in @smithy/middleware-retry, which passes a raw HTTP response.

// Before — always false for RetryErrorInfo
if (isThrottlingError(response)) {

// After — checks errorType first, falls back to isThrottlingError
if (this.isThrottlingResponse(response)) {

private isThrottlingResponse(response: any): boolean {
  if (response?.errorType) {
    return response.errorType === "THROTTLING";
  }
  return isThrottlingError(response);
}

Tests added:

• Enables rate limiter when errorType is "THROTTLING"
• Does not enable rate limiter for non-throttling errorType
• Does not call isThrottlingError when errorType is present
• Falls back to isThrottlingError when errorType is absent

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.