diff --git a/server-common/src/main/java/org/a2aproject/sdk/server/agentexecution/AgentExecutor.java b/server-common/src/main/java/org/a2aproject/sdk/server/agentexecution/AgentExecutor.java
index aba33913a..5e8e2c813 100644
--- a/server-common/src/main/java/org/a2aproject/sdk/server/agentexecution/AgentExecutor.java
+++ b/server-common/src/main/java/org/a2aproject/sdk/server/agentexecution/AgentExecutor.java
@@ -1,8 +1,8 @@
 package org.a2aproject.sdk.server.agentexecution;
 
-import org.a2aproject.sdk.server.events.EventQueue;
 import org.a2aproject.sdk.server.tasks.AgentEmitter;
 import org.a2aproject.sdk.spec.A2AError;
+import org.a2aproject.sdk.spec.TaskNotCancelableError;
 
 /**
  * Core business logic interface for implementing A2A agent functionality.
@@ -97,6 +97,7 @@
  * @see org.a2aproject.sdk.server.requesthandlers.DefaultRequestHandler
  * @see org.a2aproject.sdk.spec.AgentCard
  */
+@FunctionalInterface
 public interface AgentExecutor {
     /**
      * Executes the agent's business logic for a message.
@@ -135,7 +136,7 @@ public interface AgentExecutor {
      * <p>
      * <b>Error Handling:</b>
      * <ul>
-     *   <li>Throw {@link org.a2aproject.sdk.spec.TaskNotCancelableError} if your agent does not support
+     *   <li>Throw {@link TaskNotCancelableError} if your agent does not support
      *       cancellation at all (e.g., fire-and-forget agents)</li>
      *   <li>Throw {@link A2AError} if cancellation is supported but failed to execute
      *       (e.g., unable to interrupt running operation)</li>
@@ -144,8 +145,10 @@ public interface AgentExecutor {
      *
      * @param context the request context for the task being canceled
      * @param emitter the agent emitter for sending the cancellation event
-     * @throws org.a2aproject.sdk.spec.TaskNotCancelableError if this agent does not support cancellation
+     * @throws TaskNotCancelableError if this agent does not support cancellation
      * @throws A2AError if cancellation is supported but failed to execute
      */
-    void cancel(RequestContext context, AgentEmitter emitter) throws A2AError;
+    default void cancel(RequestContext context, AgentEmitter emitter) throws A2AError {
+        throw new TaskNotCancelableError("Agent execution is not cancelable.");
+    }
 }