STF-322: Document transport-failure retry in README and CHANGELOG

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: oschwald

CHANGELOG.md

@@ -7,6 +7,10 @@ CHANGELOG
 * Added `FAT_ZEBRA` to the `Payment.Processor` enum.
 * Added `CLEAR` to the `TransactionReport.Tag` enum for use with the Report
   Transaction API.
+* Added `WebServiceClient.Builder.maxRetries(int)` to configure transport-failure
+  retry behavior. Defaults to 1 (one retry on connection reset, broken pipe,
+  or connect timeout). Set to 0 to disable. Request-phase timeouts and HTTP
+  4xx/5xx responses are never retried.
 
 4.2.0 (2026-02-26)
 ------------------

README.md

@@ -110,6 +110,41 @@ exception will be thrown.
 
 See the API documentation for more details.
 
+### Connection pooling and transport retries ###
+
+`WebServiceClient` is thread-safe and reuses a pooled `HttpClient` across
+requests. Idle connections in the pool can be silently closed by load
+balancers or other intermediaries. When the next request reuses one of these
+half-closed connections, the JDK reports the failure as a `Connection reset`
+(or `Broken pipe`) `IOException`.
+
+To smooth over these intermittent transport failures, the SDK retries once by
+default. The retry covers:
+
+* `SocketException` with message `Connection reset` or `Broken pipe`,
+* `ConnectException`,
+* `HttpConnectTimeoutException`.
+
+Retries are **not** applied to request-phase timeouts (`HttpTimeoutException`)
+or to HTTP 4xx / 5xx responses. POST bodies are replayable, so retried
+requests are byte-identical to the original.
+
+You can change the retry budget via the builder:
+
+```java
+WebServiceClient client = new WebServiceClient.Builder(6, "ABCD567890")
+    .maxRetries(2) // up to two retries (three total attempts)
+    .build();
+```
+
+Set `.maxRetries(0)` to disable the retry entirely. Negative values throw
+`IllegalArgumentException`.
+
+If you frequently see `Connection reset` errors, you can also reduce the
+JDK's keep-alive timeout via the system property
+`jdk.httpclient.keepalive.timeout` (in seconds) to evict pooled connections
+before any intermediary does so.
+
 ### Exceptions ###
 
 Runtime exceptions: