Document behavior for 0 delay combined with jitter

Closes gh-36946

spring-core/src/main/java/org/springframework/core/retry/RetryPolicy.java

@@ -281,6 +281,11 @@ public interface RetryPolicy {
 		 * {@linkplain #maxDelay(Duration) max delay}.
 		 * <p>If a {@linkplain #multiplier(double) multiplier} is specified, it
 		 * is applied to the jitter value as well.
+		 * <p>When the configured {@linkplain #delay(Duration) delay} is zero
+		 * combined with a positive jitter, the delay never grows regardless of
+		 * any configured multiplier, so the full configured jitter is applied
+		 * directly as a random delay in the range from zero to
+		 * {@code min(jitter, maxDelay)}.
 		 * <p>The default is no jitter.
 		 * <p>The supplied value will override any previously configured value.
 		 * <p>You should not specify this configuration option if you have

spring-core/src/main/java/org/springframework/util/backoff/ExponentialBackOff.java

@@ -154,6 +154,10 @@ public class ExponentialBackOff implements BackOff {
 	 * {@code initialInterval} or above {@code maxInterval}.
 	 * <p>If a {@code multiplier} is specified, it is applied to the jitter value
 	 * as well.
+	 * <p>When {@code initialInterval} is {@code 0} combined with a positive
+	 * jitter, the interval never grows regardless of any configured multiplier,
+	 * so the full configured jitter is applied directly as a random interval in
+	 * the range from {@code 0} to {@code min(jitter, maxInterval)}.
 	 * @param jitter the jitter value in milliseconds
 	 * @since 7.0
 	 */