fix: allow omitted task push config id

extras/push-notification-config-store-database-jpa/src/main/java/org/a2aproject/sdk/extras/pushnotificationconfigstore/database/jpa/JpaDatabasePushNotificationConfigStore.java

@@ -50,10 +50,9 @@ public TaskPushNotificationConfig setInfo(TaskPushNotificationConfig notificatio
     @Override
     public TaskPushNotificationConfig setInfo(TaskPushNotificationConfig notificationConfig, @Nullable String protocolVersion) {
         String taskId = Assert.checkNotNullParam("taskId", notificationConfig.taskId());
-        // Ensure config has an ID - default to taskId if not provided (mirroring InMemoryPushNotificationConfigStore behavior)
-        if (notificationConfig.id().isEmpty()) {
-            // This means the taskId and configId are same. This will not allow having multiple configs for a single Task.
-            // The configId is a required field in the spec and should not be empty
+        // Default missing config IDs to the task ID, matching the in-memory store.
+        boolean configIdIsMissing = notificationConfig.id() == null || notificationConfig.id().isEmpty();
+        if (configIdIsMissing) {
             notificationConfig = TaskPushNotificationConfig.builder(notificationConfig).id(taskId).build();
         }
 
@@ -65,6 +64,11 @@ public TaskPushNotificationConfig setInfo(TaskPushNotificationConfig notificatio
             // Check if entity already exists
             JpaPushNotificationConfig existingJpaConfig = em.find(JpaPushNotificationConfig.class, configId);
 
+            if (configIdIsMissing && existingJpaConfig != null) {
+                throw new InvalidParamsError("A push notification config with the default ID already exists for task "
+                        + taskId + "; specify the config ID explicitly to update it");
+            }
+
             if (existingJpaConfig != null) {
                 // Update existing entity
                 existingJpaConfig.setConfig(notificationConfig);

extras/push-notification-config-store-database-jpa/src/test/java/org/a2aproject/sdk/extras/pushnotificationconfigstore/database/jpa/JpaPushNotificationConfigStoreTest.java

@@ -5,6 +5,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.never;
@@ -21,6 +22,7 @@
 import org.a2aproject.sdk.server.tasks.BasePushNotificationSender;
 import org.a2aproject.sdk.server.tasks.PushNotificationConfigStore;
 import org.a2aproject.sdk.server.tasks.PushNotificationUrlValidator;
+import org.a2aproject.sdk.spec.InvalidParamsError;
 import org.a2aproject.sdk.spec.ListTaskPushNotificationConfigsParams;
 import org.a2aproject.sdk.spec.ListTaskPushNotificationConfigsResult;
 import org.a2aproject.sdk.spec.Task;
@@ -149,18 +151,42 @@ public void testSetInfoWithoutConfigId() {
         assertEquals(1, configResult.configs().size());
         assertEquals(taskId, configResult.configs().get(0).id());
 
-        TaskPushNotificationConfig updatedConfig = TaskPushNotificationConfig.builder()
+        TaskPushNotificationConfig duplicateConfig = TaskPushNotificationConfig.builder()
                 .id("")
                 .url("http://initial.url/callback_new")
                 .taskId(taskId)
                 .build();
 
-        TaskPushNotificationConfig updatedResult = configStore.setInfo(updatedConfig);
-        assertEquals(taskId, updatedResult.id());
+        assertThrows(InvalidParamsError.class, () -> configStore.setInfo(duplicateConfig));
 
         configResult = configStore.getInfo(new ListTaskPushNotificationConfigsParams(taskId));
-        assertEquals(1, configResult.configs().size(), "Should replace existing config with same ID rather than adding new one");
-        assertEquals(updatedConfig.url(), configResult.configs().get(0).url());
+        assertEquals(1, configResult.configs().size());
+        assertEquals(initialConfig.url(), configResult.configs().get(0).url());
+    }
+
+    @Test
+    @Transactional
+    public void testSetInfoWithNullConfigId() {
+        String taskId = "task_null_config_id";
+        TaskPushNotificationConfig config = TaskPushNotificationConfig.builder()
+                .url("http://null-id.url/callback")
+                .taskId(taskId)
+                .build();
+
+        TaskPushNotificationConfig result = configStore.setInfo(config);
+
+        assertEquals(taskId, result.id(), "A missing config ID should default to the task ID");
+        ListTaskPushNotificationConfigsResult configResult = configStore.getInfo(
+                new ListTaskPushNotificationConfigsParams(taskId));
+        assertEquals(1, configResult.configs().size());
+        assertEquals(taskId, configResult.configs().get(0).id());
+
+        TaskPushNotificationConfig duplicateConfig = TaskPushNotificationConfig.builder()
+                .url("http://updated.url/callback")
+                .taskId(taskId)
+                .build();
+
+        assertThrows(InvalidParamsError.class, () -> configStore.setInfo(duplicateConfig));
     }
 
     @Test

server-common/src/main/java/org/a2aproject/sdk/server/requesthandlers/DefaultRequestHandler.java

@@ -1126,7 +1126,8 @@ public TaskPushNotificationConfig onGetTaskPushNotificationConfig(
             throw new InternalError("No push notification config found");
         }
 
-        String configId = params.id();
+        String requestedConfigId = params.id();
+        String configId = requestedConfigId == null || requestedConfigId.isEmpty() ? params.taskId() : requestedConfigId;
         return getTaskPushNotificationConfig(listTaskPushNotificationConfigsResult, configId);
     }
 

server-common/src/main/java/org/a2aproject/sdk/server/tasks/InMemoryPushNotificationConfigStore.java

@@ -48,15 +48,23 @@ public InMemoryPushNotificationConfigStore() {
     public TaskPushNotificationConfig setInfo(TaskPushNotificationConfig notificationConfig) {
         String taskId = Assert.checkNotNullParam("taskId", notificationConfig.taskId());
         TaskPushNotificationConfig.Builder builder = TaskPushNotificationConfig.builder(notificationConfig);
-        if (notificationConfig.id().isEmpty()) {
+        String requestedConfigId = notificationConfig.id();
+        boolean configIdIsMissing = requestedConfigId == null || requestedConfigId.isEmpty();
+        String configId = configIdIsMissing ? taskId : requestedConfigId;
+        if (configIdIsMissing) {
             builder.id(taskId);
         }
         TaskPushNotificationConfig config = builder.build();
-        String configId = config.id();
         int maxPerTask = PushNotificationConfigStore.maxPushConfigsPerTask(configProvider);
 
         pushNotificationInfos.compute(taskId, (key, list) -> {
             List<TaskPushNotificationConfig> mutable = list == null ? new ArrayList<>() : new ArrayList<>(list);
+            boolean defaultConfigAlreadyExists = configIdIsMissing
+                    && mutable.stream().anyMatch(existing -> existing.id() != null && existing.id().equals(configId));
+            if (defaultConfigAlreadyExists) {
+                throw new InvalidParamsError("A push notification config with the default ID already exists for task "
+                        + taskId + "; specify the config ID explicitly to update it");
+            }
             boolean isExistingConfig = mutable.removeIf(
                     existing -> existing.id() != null && existing.id().equals(configId));
             if (!isExistingConfig && mutable.size() >= maxPerTask) {

server-common/src/main/java/org/a2aproject/sdk/server/tasks/PushNotificationConfigStore.java

@@ -88,8 +88,11 @@ public interface PushNotificationConfigStore {
     /**
      * Sets or updates the push notification configuration for a task.
      * <p>
-     * If {@code notificationConfig.id()} is null or empty, it's set to the task ID.
-     * If a config with the same ID already exists for this task, it's replaced.
+     * If {@code notificationConfig.id()} is null or empty, the store creates the
+     * default config with the task ID. Omitting the ID is a create-only shorthand:
+     * if the default config already exists, the store rejects the request instead
+     * of silently replacing it. To update the default config, provide the task ID
+     * explicitly. Configurations beyond the default one must always provide an ID.
      * </p>
      *
      * @param notificationConfig the task push notification configuration

server-common/src/test/java/org/a2aproject/sdk/server/requesthandlers/DefaultRequestHandlerTest.java

@@ -45,6 +45,7 @@
 import org.a2aproject.sdk.spec.CancelTaskParams;
 import org.a2aproject.sdk.spec.Event;
 import org.a2aproject.sdk.spec.EventKind;
+import org.a2aproject.sdk.spec.GetTaskPushNotificationConfigParams;
 import org.a2aproject.sdk.spec.InvalidParamsError;
 import org.a2aproject.sdk.spec.ListTasksParams;
 import org.a2aproject.sdk.spec.ListTaskPushNotificationConfigsParams;
@@ -989,6 +990,26 @@ void testVersionStored_OnCreateTaskPushNotificationConfig() throws Exception {
             "Protocol version should be stored for the push notification config");
     }
 
+    @Test
+    void testGetTaskPushNotificationConfigDefaultsMissingIdToTaskId() throws Exception {
+        String taskId = "get-default-config-id";
+        taskStore.save(Task.builder()
+                .id(taskId)
+                .contextId("ctx-get-default-config-id")
+                .status(new TaskStatus(TaskState.TASK_STATE_WORKING))
+                .build(), false);
+        requestHandler.onCreateTaskPushNotificationConfig(TaskPushNotificationConfig.builder()
+                .taskId(taskId)
+                .url("http://example.com/get-default-config-id")
+                .build(), NULL_CONTEXT);
+
+        TaskPushNotificationConfig result = requestHandler.onGetTaskPushNotificationConfig(
+                new GetTaskPushNotificationConfigParams(taskId), NULL_CONTEXT);
+
+        assertEquals(taskId, result.id());
+        assertEquals("http://example.com/get-default-config-id", result.url());
+    }
+
     /**
      * Verify that onMessageSend stores the protocol version when the request
      * includes a push notification config (new task path).

server-common/src/test/java/org/a2aproject/sdk/server/tasks/InMemoryPushNotificationConfigStoreTest.java

@@ -151,10 +151,10 @@ public void testSetInfoAppendsToExistingConfig() {
     }
 
     @Test
-    public void testSetInfoWithoutConfigId() {
+    public void testSetInfoWithEmptyConfigId() {
         String taskId = "task1";
         TaskPushNotificationConfig initialConfig = TaskPushNotificationConfig.builder()
-                .id("") // No ID set
+                .id("")
                 .url("http://initial.url/callback")
                 .taskId(taskId)
                 .build();
@@ -166,18 +166,37 @@ public void testSetInfoWithoutConfigId() {
         assertEquals(1, configResult.configs().size());
         assertEquals(taskId, configResult.configs().get(0).id());
 
-        TaskPushNotificationConfig updatedConfig = TaskPushNotificationConfig.builder()
-                .id("") // No ID set
+        TaskPushNotificationConfig duplicateConfig = TaskPushNotificationConfig.builder()
+                .id("")
                 .url("http://initial.url/callback_new")
                 .taskId(taskId)
                 .build();
 
-        TaskPushNotificationConfig updatedResult = configStore.setInfo(updatedConfig);
-        assertEquals(taskId, updatedResult.id());
+        assertThrows(InvalidParamsError.class, () -> configStore.setInfo(duplicateConfig));
 
         configResult = configStore.getInfo(new ListTaskPushNotificationConfigsParams(taskId));
-        assertEquals(1, configResult.configs().size(), "Should replace existing config with same ID rather than adding new one");
-        assertEquals(updatedConfig.url(), configResult.configs().get(0).url());
+        assertEquals(1, configResult.configs().size());
+        assertEquals(initialConfig.url(), configResult.configs().get(0).url());
+    }
+
+    @Test
+    public void testSetInfoWithNullConfigId() {
+        String taskId = "task_with_null_config_id";
+        TaskPushNotificationConfig config = TaskPushNotificationConfig.builder()
+                .url("http://initial.url/callback")
+                .taskId(taskId)
+                .build();
+
+        TaskPushNotificationConfig result = configStore.setInfo(config);
+
+        assertEquals(taskId, result.id(), "Config ID should default to taskId when null");
+
+        TaskPushNotificationConfig duplicateConfig = TaskPushNotificationConfig.builder()
+                .url("http://updated.url/callback")
+                .taskId(taskId)
+                .build();
+
+        assertThrows(InvalidParamsError.class, () -> configStore.setInfo(duplicateConfig));
     }
 
     @Test

spec/src/main/java/org/a2aproject/sdk/spec/GetTaskPushNotificationConfigParams.java

@@ -18,29 +18,37 @@
  * @see TaskPushNotificationConfig for the returned configuration structure
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record GetTaskPushNotificationConfigParams(String taskId, String id, @Nullable String tenant) {
+public record GetTaskPushNotificationConfigParams(String taskId, @Nullable String id, @Nullable String tenant) {
 
     /**
      * Compact constructor that validates required fields.
      *
      * @param taskId the taskId parameter (see class-level JavaDoc)
      * @param id the id parameter (see class-level JavaDoc)
      * @param tenant the tenant parameter (see class-level JavaDoc)
-     * @throws IllegalArgumentException if taskId or tenant is null
+     * @throws IllegalArgumentException if taskId is null
      */
     public GetTaskPushNotificationConfigParams {
         Assert.checkNotNullParam("taskId", taskId);
-        Assert.checkNotNullParam("id", id);
         Utils.validateTenant(tenant);
     }
 
+    /**
+     * Convenience constructor for retrieving the configuration that uses the task ID as its default ID.
+     *
+     * @param taskId the task identifier (required)
+     */
+    public GetTaskPushNotificationConfigParams(String taskId) {
+        this(taskId, null, null);
+    }
+
     /**
      * Convenience constructor for creating parameters without tenant.
      *
      * @param taskId the task identifier (required)
      * @param id optional configuration ID to retrieve
      */
-    public GetTaskPushNotificationConfigParams(String taskId, String id) {
+    public GetTaskPushNotificationConfigParams(String taskId, @Nullable String id) {
         this(taskId, id, null);
     }
 
@@ -84,7 +92,7 @@ public Builder taskId(String taskId) {
          * @param id the configuration ID
          * @return this builder for method chaining
          */
-        public Builder id(String id) {
+        public Builder id(@Nullable String id) {
             this.id = id;
             return this;
         }
@@ -108,7 +116,7 @@ public Builder tenant(@Nullable String tenant) {
         public GetTaskPushNotificationConfigParams build() {
             return new GetTaskPushNotificationConfigParams(
                     Assert.checkNotNullParam("taskId", taskId),
-                    Assert.checkNotNullParam("id", id),
+                    id,
                     tenant);
         }
     }

spec/src/main/java/org/a2aproject/sdk/spec/TaskPushNotificationConfig.java

@@ -21,7 +21,8 @@
  * Used for managing task-specific push notification settings via the push notification
  * management methods ({@code tasks/pushNotificationConfig/set}, {@code tasks/pushNotificationConfig/get}, etc.).
  *
- * @param id unique identifier (e.g. UUID) for this push notification configuration
+ * @param id optional unique identifier (e.g. UUID) for this push notification configuration.
+ *        When omitted while creating a configuration, the server assigns one.
  * @param taskId the unique identifier of the task to receive push notifications for
  * @param url the HTTP/HTTPS endpoint URL to receive push notifications (required)
  * @param token optional bearer token for simple authentication
@@ -31,22 +32,21 @@
  * @see MessageSendConfiguration for configuring push notifications on message send
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record TaskPushNotificationConfig(String id, @Nullable String taskId, String url, @Nullable String token,
+public record TaskPushNotificationConfig(@Nullable String id, @Nullable String taskId, String url, @Nullable String token,
         @Nullable AuthenticationInfo authentication, @Nullable String tenant) {
 
     /**
      * Compact constructor for validation.
      * Validates that required parameters are not null.
      *
-     * @param id the configuration identifier
+     * @param id the optional configuration identifier
      * @param taskId the task identifier
      * @param url the notification endpoint URL
      * @param token optional bearer token
      * @param authentication optional authentication info
      * @param tenant the tenant identifier
      */
     public TaskPushNotificationConfig {
-        Assert.checkNotNullParam("id", id);
         Assert.checkNotNullParam("url", url);
         Utils.validateTenant(tenant);
     }
@@ -105,10 +105,10 @@ private Builder(TaskPushNotificationConfig config) {
         /**
          * Sets the configuration identifier.
          *
-         * @param id the configuration ID
+         * @param id the optional configuration ID
          * @return this builder
          */
-        public Builder id(String id) {
+        public Builder id(@Nullable String id) {
             this.id = id;
             return this;
         }
@@ -172,11 +172,11 @@ public Builder tenant(String tenant) {
          * Builds the {@link TaskPushNotificationConfig}.
          *
          * @return a new push notification configuration
-         * @throws IllegalArgumentException if id or url is null
+         * @throws IllegalArgumentException if url is null
          */
         public TaskPushNotificationConfig build() {
             return new TaskPushNotificationConfig(
-                    Assert.checkNotNullParam("id", id),
+                    id,
                     taskId,
                     Assert.checkNotNullParam("url", url),
                     token,

spec/src/test/java/org/a2aproject/sdk/spec/GetTaskPushNotificationConfigParamsTest.java

@@ -0,0 +1,26 @@
+package org.a2aproject.sdk.spec;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+class GetTaskPushNotificationConfigParamsTest {
+
+    @Test
+    void testConstructionAllowsOmittedConfigurationId() {
+        GetTaskPushNotificationConfigParams params = new GetTaskPushNotificationConfigParams("task-1");
+
+        assertEquals("task-1", params.taskId());
+        assertNull(params.id());
+    }
+
+    @Test
+    void testBuilderAllowsOmittedConfigurationId() {
+        GetTaskPushNotificationConfigParams params = GetTaskPushNotificationConfigParams.builder()
+                .taskId("task-1")
+                .build();
+
+        assertNull(params.id());
+    }
+}