Mark the SSE and WebSocket modules as experimental

Annotated the public API types of the httpclient5-sse and httpclient5-websocket modules
with @experimental. Both modules expose a large API surface that is not yet stable, and the
annotation marks them as subject to change so that a relaxed compatibility policy applies for
the 5.7 release series; the japicmp binary and source compatibility checks are already skipped
for both modules. Types that are already marked @internal are left unchanged.

Author: arturobernalg

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/BackoffStrategy.java

@@ -26,12 +26,15 @@
  */
 package org.apache.hc.client5.http.sse;
 
+import org.apache.hc.core5.annotation.Experimental;
+
 /**
  * Computes the next reconnect delay for SSE (in milliseconds).
  * <p>
  * Implementations may also override {@link #shouldReconnect(int, long, Long)}
  * to decline reconnects entirely (e.g., a "no strategy" that never reconnects).
  */
+@Experimental
 public interface BackoffStrategy {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/EventSource.java

@@ -29,6 +29,7 @@
 import java.util.Map;
 
 import org.apache.hc.core5.annotation.Contract;
+import org.apache.hc.core5.annotation.Experimental;
 
 /**
  * Represents a Server-Sent Events (SSE) connection to a remote resource.
@@ -52,6 +53,7 @@
  * @since 5.7
  */
 @Contract
+@Experimental
 public interface EventSource {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/EventSourceConfig.java

@@ -29,6 +29,7 @@
 import java.util.Objects;
 
 import org.apache.hc.client5.http.sse.impl.ExponentialJitterBackoff;
+import org.apache.hc.core5.annotation.Experimental;
 
 /**
  * Immutable configuration for {@link EventSource} behavior, primarily covering
@@ -50,6 +51,7 @@
  *
  * @since 5.7
  */
+@Experimental
 public final class EventSourceConfig {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/EventSourceListener.java

@@ -26,6 +26,8 @@
  */
 package org.apache.hc.client5.http.sse;
 
+import org.apache.hc.core5.annotation.Experimental;
+
 /**
  * Callback interface for receiving Server-Sent Events (SSE) and lifecycle
  * notifications from an {@link EventSource}.
@@ -58,6 +60,7 @@
  * @since 5.7
  */
 @FunctionalInterface
+@Experimental
 public interface EventSourceListener {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/SseExecutor.java

@@ -40,6 +40,7 @@
 import org.apache.hc.client5.http.impl.nio.PoolingAsyncClientConnectionManagerBuilder;
 import org.apache.hc.client5.http.sse.impl.DefaultEventSource;
 import org.apache.hc.client5.http.sse.impl.SseParser;
+import org.apache.hc.core5.annotation.Experimental;
 import org.apache.hc.core5.reactor.IOReactorStatus;
 import org.apache.hc.core5.util.Args;
 import org.apache.hc.core5.util.TimeValue;
@@ -82,6 +83,7 @@
  *
  * @since 5.7
  */
+@Experimental
 public final class SseExecutor {
 
     // Visible for tests

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/SseExecutorBuilder.java

@@ -34,6 +34,7 @@
 
 import org.apache.hc.client5.http.impl.async.CloseableHttpAsyncClient;
 import org.apache.hc.client5.http.sse.impl.SseParser;
+import org.apache.hc.core5.annotation.Experimental;
 import org.apache.hc.core5.util.Args;
 
 /**
@@ -62,6 +63,7 @@
  *
  * @since 5.7
  */
+@Experimental
 public final class SseExecutorBuilder {
 
     private CloseableHttpAsyncClient client;

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/impl/ExponentialJitterBackoff.java

@@ -29,6 +29,7 @@
 import java.util.concurrent.ThreadLocalRandom;
 
 import org.apache.hc.client5.http.sse.BackoffStrategy;
+import org.apache.hc.core5.annotation.Experimental;
 
 /**
  * Backoff strategy that computes exponential delays with <em>full jitter</em> and
@@ -51,6 +52,7 @@
  *
  * @since 5.7
  */
+@Experimental
 public final class ExponentialJitterBackoff implements BackoffStrategy {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/impl/FixedBackoffStrategy.java

@@ -28,6 +28,7 @@
 
 import org.apache.hc.client5.http.sse.BackoffStrategy;
 import org.apache.hc.client5.http.sse.EventSourceConfig;
+import org.apache.hc.core5.annotation.Experimental;
 
 /**
  * Backoff strategy that uses a fixed delay between reconnect attempts and
@@ -49,6 +50,7 @@
  * @see EventSourceConfig
  * @since 5.7
  */
+@Experimental
 public final class FixedBackoffStrategy implements BackoffStrategy {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/impl/NoBackoffStrategy.java

@@ -27,6 +27,7 @@
 package org.apache.hc.client5.http.sse.impl;
 
 import org.apache.hc.client5.http.sse.BackoffStrategy;
+import org.apache.hc.core5.annotation.Experimental;
 
 /**
  * Backoff policy that <strong>never reconnects</strong>.
@@ -45,6 +46,7 @@
  *
  * @since 5.7
  */
+@Experimental
 public final class NoBackoffStrategy implements BackoffStrategy {
 
     /**

httpclient5-sse/src/main/java/org/apache/hc/client5/http/sse/impl/SseParser.java

@@ -26,6 +26,8 @@
  */
 package org.apache.hc.client5.http.sse.impl;
 
+import org.apache.hc.core5.annotation.Experimental;
+
 /**
  * Parser strategy for SSE entity consumption.
  *
@@ -38,6 +40,7 @@
  *
  * @since 5.7
  */
+@Experimental
 public enum SseParser {
     /**
      * CharBuffer → spec reader.