Add SimplePlugin context propagators to activity clients

SimplePlugin.addContextPropagators configured workflow clients but not
activity clients, so standalone activities started through a plugin-
configured ActivityClient carried no propagated headers.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: patbeqo

temporal-sdk/src/main/java/io/temporal/common/SimplePlugin.java

@@ -259,6 +259,15 @@ public void configureScheduleClient(@Nonnull ScheduleClientOptions.Builder build
 
   @Override
   public void configureActivityClient(@Nonnull ActivityClientOptions.Builder builder) {
+    // Add context propagators
+    if (!contextPropagators.isEmpty()) {
+      List<ContextPropagator> existing = builder.build().getContextPropagators();
+      List<ContextPropagator> combined = new ArrayList<>(existing);
+      combined.addAll(contextPropagators);
+      builder.setContextPropagators(combined);
+    }
+
+    // Add client interceptors
     if (!activityClientInterceptors.isEmpty()) {
       List<ActivityClientInterceptor> combined = new ArrayList<>(builder.build().getInterceptors());
       combined.addAll(activityClientInterceptors);

temporal-sdk/src/test/java/io/temporal/common/SimplePluginBuilderTest.java

@@ -30,6 +30,7 @@
 import io.temporal.client.WorkflowClientOptions;
 import io.temporal.client.schedules.ScheduleClientOptions;
 import io.temporal.client.schedules.ScheduleClientPlugin;
+import io.temporal.common.context.ContextPropagator;
 import io.temporal.common.converter.DataConverter;
 import io.temporal.common.interceptors.ActivityClientInterceptor;
 import io.temporal.common.interceptors.ActivityClientInterceptorBase;
@@ -88,6 +89,18 @@ public void testAddWorkerInterceptors() {
     assertSame(interceptor, interceptors[0]);
   }
 
+  @Test
+  public void testAddContextPropagatorsToActivityClient() {
+    ContextPropagator propagator = mock(ContextPropagator.class);
+
+    SimplePlugin plugin = SimplePlugin.newBuilder("test").addContextPropagators(propagator).build();
+
+    ActivityClientOptions.Builder builder = ActivityClientOptions.newBuilder();
+    ((ActivityClientPlugin) plugin).configureActivityClient(builder);
+
+    assertEquals(Collections.singletonList(propagator), builder.build().getContextPropagators());
+  }
+
   @Test
   public void testAddClientInterceptors() {
     WorkflowClientInterceptor interceptor = new WorkflowClientInterceptorBase() {};