Fix UnsupportedOperationException when merging ActivityOptions with immutable context propagators

The mergeActivityOptions method was calling addAll() directly on the existing
contextPropagators list, which fails when the list is immutable (e.g., created
with List.of() or Collections.emptyList()).

This fix creates a new ArrayList that combines both lists instead of modifying
the existing one.

Fixes #2482

Author: nitishagar

temporal-sdk/src/main/java/io/temporal/activity/ActivityOptions.java

@@ -6,6 +6,7 @@
 import io.temporal.common.context.ContextPropagator;
 import io.temporal.failure.CanceledFailure;
 import java.time.Duration;
+import java.util.ArrayList;
 import java.util.List;
 
 /** Options used to configure how an activity is invoked. */
@@ -282,7 +283,9 @@ public Builder mergeActivityOptions(ActivityOptions override) {
       if (this.contextPropagators == null) {
         this.contextPropagators = override.contextPropagators;
       } else if (override.contextPropagators != null) {
-        this.contextPropagators.addAll(override.contextPropagators);
+        List<ContextPropagator> merged = new ArrayList<>(this.contextPropagators);
+        merged.addAll(override.contextPropagators);
+        this.contextPropagators = merged;
       }
       if (override.versioningIntent != VersioningIntent.VERSIONING_INTENT_UNSPECIFIED) {
         this.versioningIntent = override.versioningIntent;

temporal-sdk/src/test/java/io/temporal/activity/ActivityOptionsTest.java

@@ -9,6 +9,7 @@
 import io.temporal.workflow.shared.TestActivities.TestActivityImpl;
 import java.lang.reflect.Method;
 import java.time.Duration;
+import java.util.Collections;
 import java.util.Map;
 import org.junit.*;
 import org.junit.rules.Timeout;
@@ -62,6 +63,31 @@ public void testActivityOptionsMerge() {
     Assert.assertEquals(methodOps1, merged);
   }
 
+  @Test
+  public void testActivityOptionsMergeWithImmutableContextPropagators() {
+    // Create options with immutable lists using Collections.emptyList()
+    // This tests the fix for https://github.com/temporalio/sdk-java/issues/2482
+    ActivityOptions options1 =
+        ActivityOptions.newBuilder()
+            .setStartToCloseTimeout(Duration.ofSeconds(1))
+            .setContextPropagators(Collections.emptyList())
+            .build();
+
+    ActivityOptions options2 =
+        ActivityOptions.newBuilder()
+            .setStartToCloseTimeout(Duration.ofSeconds(2))
+            .setContextPropagators(Collections.emptyList())
+            .build();
+
+    // This should NOT throw UnsupportedOperationException
+    ActivityOptions merged =
+        ActivityOptions.newBuilder(options1).mergeActivityOptions(options2).build();
+
+    assertNotNull(merged);
+    assertNotNull(merged.getContextPropagators());
+    assertEquals(Duration.ofSeconds(2), merged.getStartToCloseTimeout());
+  }
+
   @Test
   public void testActivityOptionsDefaultInstance() {
     testEnv.registerActivitiesImplementations(new TestActivityImpl());