Fix remaining collection getter defensive copies in events and json packages

Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Author: Copilot

src/main/java/com/github/copilot/sdk/events/SubagentSelectedEvent.java

@@ -60,7 +60,7 @@ public void setAgentDisplayName(String agentDisplayName) {
         }
 
         public String[] getTools() {
-            return tools;
+            return tools == null ? null : tools.clone();
         }
 
         public void setTools(String[] tools) {

src/main/java/com/github/copilot/sdk/events/ToolExecutionCompleteEvent.java

@@ -7,6 +7,7 @@
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
+import java.util.Collections;
 import java.util.Map;
 
 /**
@@ -98,7 +99,7 @@ public void setError(Error error) {
         }
 
         public Map<String, Object> getToolTelemetry() {
-            return toolTelemetry;
+            return toolTelemetry == null ? null : Collections.unmodifiableMap(toolTelemetry);
         }
 
         public void setToolTelemetry(Map<String, Object> toolTelemetry) {

src/main/java/com/github/copilot/sdk/events/UserMessageEvent.java

@@ -7,6 +7,7 @@
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
+import java.util.Collections;
 import java.util.List;
 
 /**
@@ -65,7 +66,7 @@ public void setTransformedContent(String transformedContent) {
         }
 
         public List<Attachment> getAttachments() {
-            return attachments;
+            return attachments == null ? null : Collections.unmodifiableList(attachments);
         }
 
         public void setAttachments(List<Attachment> attachments) {

src/main/java/com/github/copilot/sdk/json/CustomAgentConfig.java

@@ -4,6 +4,7 @@
 
 package com.github.copilot.sdk.json;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
@@ -128,7 +129,7 @@ public CustomAgentConfig setDescription(String description) {
      * @return the list of tool identifiers
      */
     public List<String> getTools() {
-        return tools;
+        return tools == null ? null : Collections.unmodifiableList(tools);
     }
 
     /**
@@ -175,7 +176,7 @@ public CustomAgentConfig setPrompt(String prompt) {
      * @return the MCP servers map
      */
     public Map<String, Object> getMcpServers() {
-        return mcpServers;
+        return mcpServers == null ? null : Collections.unmodifiableMap(mcpServers);
     }
 
     /**

src/main/java/com/github/copilot/sdk/json/MessageOptions.java

@@ -4,6 +4,7 @@
 
 package com.github.copilot.sdk.json;
 
+import java.util.Collections;
 import java.util.List;
 
 import com.fasterxml.jackson.annotation.JsonInclude;
@@ -60,7 +61,7 @@ public MessageOptions setPrompt(String prompt) {
      * @return the list of attachments
      */
     public List<Attachment> getAttachments() {
-        return attachments;
+        return attachments == null ? null : Collections.unmodifiableList(attachments);
     }
 
     /**