Address PR review: thread safety, comments, and test fixes

- Add synchronized to rate-limit state methods to fix check-then-act
  race condition
- Add comments explaining defensive 429 and non-standard 460 in
  isStatusRetryWithBackoff
- Fix outdated test comments and line references
- Widen timing assertion upper bound (3s → 5s) to reduce CI flakiness

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MichaelGHSeg

analytics/src/main/java/com/segment/analytics/internal/AnalyticsClient.java

@@ -229,7 +229,7 @@ public void flush() {
     }
   }
 
-  void setRateLimitState(long retryAfterSeconds) {
+  synchronized void setRateLimitState(long retryAfterSeconds) {
     long now = System.currentTimeMillis();
     if (rateLimitStartTime == 0) {
       rateLimitStartTime = now;
@@ -238,13 +238,13 @@ void setRateLimitState(long retryAfterSeconds) {
     rateLimited = true;
   }
 
-  void clearRateLimitState() {
+  synchronized void clearRateLimitState() {
     rateLimited = false;
     rateLimitWaitUntil = 0;
     rateLimitStartTime = 0;
   }
 
-  boolean isRateLimited() {
+  synchronized boolean isRateLimited() {
     if (!rateLimited) return false;
     if (System.currentTimeMillis() >= rateLimitWaitUntil) {
       rateLimited = false;
@@ -702,7 +702,10 @@ public void run() {
     }
 
     private static boolean isStatusRetryWithBackoff(int status) {
-      // Explicitly retry these client errors
+      // Explicitly retry these client errors.
+      // 429 is also handled earlier via isStatusRetryAfterEligible (RATE_LIMITED strategy);
+      // including it here is defensive in case call-site ordering changes.
+      // 460 is a non-standard, Segment-specific status code for transient retryable failures.
       if (status == 408 || status == 410 || status == 429 || status == 460) {
         return true;
       }

analytics/src/test/java/com/segment/analytics/internal/AnalyticsClientTest.java

@@ -618,8 +618,7 @@ public Call<UploadResponse> answer(InvocationOnMock invocation) {
     BatchUploadTask batchUploadTask = new BatchUploadTask(client, BACKO, batch, 10);
     batchUploadTask.run();
 
-    // DEFAULT_RETRIES == maxRetries
-    // tries 11(one normal run + 10 retries) even though default is 50 in AnalyticsClient.java
+    // maxRetries=10 => tries 11 (one initial attempt + 10 retries)
     verify(segmentService, times(11)).upload(anyInt(), isNull(), eq(batch));
     verify(callback)
         .failure(
@@ -732,7 +731,7 @@ public void retryAfterHeaderRespectsShortDelay() {
     Batch batch = batchFor(trackMessage);
 
     // Test with a short Retry-After delay (2 seconds) to verify the mechanism works
-    // The cap at 300 seconds is verified by code inspection at AnalyticsClient.java:556-558
+    // The cap at 300 seconds is verified by code inspection at AnalyticsClient.java:610-612
     Response<UploadResponse> rateLimitedWithShortDelay = errorWithRetryAfter(429, "2");
     Response<UploadResponse> successResponse = Response.success(200, response);
 
@@ -747,7 +746,7 @@ public void retryAfterHeaderRespectsShortDelay() {
 
     // Should wait approximately 2 seconds
     long elapsedMs = endTime - startTime;
-    assertThat(elapsedMs).isGreaterThanOrEqualTo(2000L).isLessThan(3000L);
+    assertThat(elapsedMs).isGreaterThanOrEqualTo(2000L).isLessThan(5000L);
 
     verify(segmentService, times(2)).upload(anyInt(), isNull(), eq(batch));
     verify(callback).success(trackMessage);