fix(retry): address PR #12 code review feedback

- Add 'stepped' backoff strategy that uses RETRY_BACKOFF_DELAYS directly
- Update rsocket config to use 'stepped' instead of 'exponential'
- Clarify maxWebSocketListeners calculation (8 core + 10 dynamic + 2 buffer)
- Document maxSocketClientListeners calculation (20 core + 20 dynamic + 10 buffer)
- Change 'exponential backoff' to 'custom progressive backoff' in docs
- Add comprehensive tests for getRetryDelayWithJitter and getAllRetryDelaysWithJitter
- Fix existing test type errors (onRetry mock, always/never predicates)

src/Utils/retry-utils.ts

@@ -33,7 +33,7 @@ const RETRY_JITTER_FACTOR = 0.15
 /**
  * Backoff strategies
  */
-export type BackoffStrategy = 'exponential' | 'linear' | 'constant' | 'fibonacci'
+export type BackoffStrategy = 'exponential' | 'linear' | 'constant' | 'fibonacci' | 'stepped'
 
 /**
  * Retry configuration options
@@ -152,6 +152,14 @@ export function calculateDelay(
 			break
 		}
 
+		case 'stepped': {
+			// Uses pre-defined delay array directly (ignores baseDelay/multiplier)
+			// Falls back to last delay if attempt exceeds array length
+			const index = Math.min(attempt - 1, RETRY_BACKOFF_DELAYS.length - 1)
+			delay = RETRY_BACKOFF_DELAYS[index] ?? RETRY_BACKOFF_DELAYS[0] ?? baseDelay
+			break
+		}
+
 		default:
 			delay = baseDelay
 	}
@@ -646,14 +654,15 @@ export const retryConfigs = {
 	},
 
 	/**
-	 * RSocket-style retry (uses RETRY_BACKOFF_DELAYS from Defaults)
-	 * Delays: 1s, 2s, 5s, 10s, 20s with jitter
+	 * RSocket-style retry with stepped delays
+	 * Uses fixed delay array: 1s, 2s, 5s, 10s, 20s (with ±15% jitter)
+	 * Unlike exponential, this uses exact delays from RETRY_BACKOFF_DELAYS
 	 */
 	rsocket: {
 		maxAttempts: RETRY_BACKOFF_DELAYS.length,
 		baseDelay: RETRY_BACKOFF_DELAYS[0],
 		maxDelay: RETRY_BACKOFF_DELAYS[RETRY_BACKOFF_DELAYS.length - 1],
-		backoffStrategy: 'exponential' as const,
+		backoffStrategy: 'stepped' as const,
 		jitter: RETRY_JITTER_FACTOR,
 	},
 }