feat: add background task notification system (#827)

Co-authored-by: Letta <noreply@letta.com>

src/tools/impl/TaskOutput.ts

@@ -0,0 +1,30 @@
+import { getTaskOutput } from "./BashOutput.js";
+import { validateRequiredParams } from "./validation.js";
+
+interface TaskOutputArgs {
+  task_id: string;
+  block?: boolean;
+  timeout?: number;
+}
+
+interface TaskOutputResult {
+  message: string;
+  status?: "running" | "completed" | "failed";
+}
+
+/**
+ * TaskOutput - retrieves output from a running or completed background task.
+ * Supports blocking (wait for completion) and timeout.
+ */
+export async function task_output(
+  args: TaskOutputArgs,
+): Promise<TaskOutputResult> {
+  validateRequiredParams(args, ["task_id"], "TaskOutput");
+  const { task_id, block = true, timeout = 30000 } = args;
+
+  return getTaskOutput({
+    task_id,
+    block,
+    timeout,
+  });
+}