docs(bigquery): add javadoc comments to retry-wrapping helper methods

Author: jinseopkim0

java-bigquery/google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/BigQueryImpl.java

@@ -2413,6 +2413,12 @@ private static boolean isRetryErrorCodeHttpNotFound(BigQueryRetryHelperException
     return false;
   }
 
+  /**
+   * Helper to retrieve the retry algorithm wrapped for safe HTTP 5xx error retries.
+   *
+   * <p>This delegates to {@link BigQueryRetryHelper#maybeWrapForHttpRetry} to ensure safe
+   * conditional wrapping of the default algorithm while leaving custom user algorithms untouched.
+   */
   @SuppressWarnings("unchecked")
   private <V> ResultRetryAlgorithm<V> getRetryAlgorithmWithHttpRetry() {
     return BigQueryRetryHelper.maybeWrapForHttpRetry(

java-bigquery/google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/BigQueryRetryHelper.java

@@ -121,6 +121,14 @@ private static <V> V run(
     return retryingFuture.get();
   }
 
+  /**
+   * Conditionally wraps the provided retry algorithm with a wrapper that retries on transient HTTP
+   * 5xx errors (500, 502, 503, 504).
+   *
+   * <p>Wrapping only occurs if the provided algorithm is the default {@link
+   * BigQueryBaseService#DEFAULT_BIGQUERY_EXCEPTION_HANDLER}. Custom user-defined retry algorithms
+   * are returned unmodified to preserve custom retry policies.
+   */
   static <V> ResultRetryAlgorithm<V> maybeWrapForHttpRetry(ResultRetryAlgorithm<V> algorithm) {
     if (algorithm == BigQueryBaseService.DEFAULT_BIGQUERY_EXCEPTION_HANDLER) {
       return wrapDefaultAlgorithm(algorithm);