chore: Add lastUpdatedAt to Task

Author: He-Pin

docs/specification/draft/basic/utilities/tasks.mdx

@@ -160,6 +160,7 @@ To create a task, requestors send a request with the `task` field included in th
       "status": "working",
       "statusMessage": "The operation is now in progress.",
       "createdAt": "2025-11-25T10:30:00Z",
+      "lastUpdatedAt": "2025-11-25T10:40:00Z",
       "ttl": 60000,
       "pollInterval": 5000
     }
@@ -219,6 +220,7 @@ Requestors **SHOULD** continue polling until the task reaches a terminal status
     "status": "working",
     "statusMessage": "The operation is now in progress.",
     "createdAt": "2025-11-25T10:30:00Z",
+    "lastUpdatedAt": "2025-11-25T10:40:00Z",
     "ttl": 30000,
     "pollInterval": 5000
   }
@@ -291,6 +293,7 @@ When a task status changes, receivers **MAY** send a [`notifications/tasks/statu
     "taskId": "786512e2-9e0d-44bd-8f29-789f320fe840",
     "status": "completed",
     "createdAt": "2025-11-25T10:30:00Z",
+    "lastUpdatedAt": "2025-11-25T10:50:00Z",
     "ttl": 60000,
     "pollInterval": 5000
   }
@@ -330,13 +333,15 @@ To retrieve a list of tasks, requestors can send a [`tasks/list`](/specification
         "taskId": "786512e2-9e0d-44bd-8f29-789f320fe840",
         "status": "working",
         "createdAt": "2025-11-25T10:30:00Z",
+        "lastUpdatedAt": "2025-11-25T10:40:00Z",
         "ttl": 30000,
         "pollInterval": 5000
       },
       {
         "taskId": "abc123-def456-ghi789",
         "status": "completed",
         "createdAt": "2025-11-25T09:15:00Z",
+        "lastUpdatedAt": "2025-11-25T10:40:00Z",
         "ttl": 60000
       }
     ],
@@ -373,6 +378,7 @@ To explicitly cancel a task, requestors can send a [`tasks/cancel`](/specificati
     "status": "cancelled",
     "statusMessage": "The task was cancelled by request.",
     "createdAt": "2025-11-25T10:30:00Z",
+    "lastUpdatedAt": "2025-11-25T10:40:00Z",
     "ttl": 30000,
     "pollInterval": 5000
   }
@@ -448,6 +454,7 @@ While this note is not prescriptive regarding the specific usage of SSE streams,
 ### TTL and Resource Management
 
 1. Receivers **MUST** include a `createdAt` [ISO 8601](https://datatracker.ietf.org/doc/html/rfc3339#section-5)-formatted timestamp in all task responses to indicate when the task was created.
+1. Receivers **MUST** include a `lastUpdatedAt` [ISO 8601](https://datatracker.ietf.org/doc/html/rfc3339#section-5)-formatted timestamp in all task responses to indicate when the task was last updated.
 1. Receivers **MAY** override the requested `ttl` duration.
 1. Receivers **MUST** include the actual `ttl` duration (or `null` for unlimited) in `tasks/get` responses.
 1. After a task's `ttl` lifetime has elapsed, receivers **MAY** delete the task and its results, regardless of the task status.
@@ -704,6 +711,7 @@ A task represents the execution state of a request. The task state includes:
 - `createdAt`: ISO 8601 timestamp when the task was created
 - `ttl`: Time in milliseconds from creation before task may be deleted
 - `pollInterval`: Suggested time in milliseconds between status checks
+- `lastUpdatedAt`: ISO 8601 timestamp when the task status was last updated
 
 ### Task Status
 
@@ -842,6 +850,7 @@ When the underlying request does not complete successfully, the task moves to th
     "taskId": "786512e2-9e0d-44bd-8f29-789f820fe840",
     "status": "failed",
     "createdAt": "2025-11-25T10:30:00Z",
+    "lastUpdatedAt": "2025-11-25T10:40:00Z",
     "ttl": 30000,
     "statusMessage": "Tool execution failed: API rate limit exceeded"
   }

docs/specification/draft/schema.mdx

@@ -1360,6 +1360,11 @@ export interface Task {
    */
   createdAt: string;
 
+  /**
+   * ISO 8601 timestamp when the task was last updated.
+   */
+  lastUpdatedAt: string;
+
   /**
    * Actual retention duration from creation in milliseconds, null for unlimited.
    */