chore(a2a-server): if a2a task creation fails return error to user (#8106)

Co-authored-by: cornmander <shikhman@google.com>

packages/a2a-server/src/utils/executor_utils.ts

@@ -0,0 +1,52 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { Message } from '@a2a-js/sdk';
+import type { ExecutionEventBus } from '@a2a-js/sdk/server';
+import { v4 as uuidv4 } from 'uuid';
+
+import { CoderAgentEvent } from '../types.js';
+import type { StateChange } from '../types.js';
+
+export async function pushTaskStateFailed(
+  error: unknown,
+  eventBus: ExecutionEventBus,
+  taskId: string,
+  contextId: string,
+) {
+  const errorMessage =
+    error instanceof Error ? error.message : 'Agent execution error';
+  const stateChange: StateChange = {
+    kind: CoderAgentEvent.StateChangeEvent,
+  };
+  eventBus.publish({
+    kind: 'status-update',
+    taskId,
+    contextId,
+    status: {
+      state: 'failed',
+      message: {
+        kind: 'message',
+        role: 'agent',
+        parts: [
+          {
+            kind: 'text',
+            text: errorMessage,
+          },
+        ],
+        messageId: uuidv4(),
+        taskId,
+        contextId,
+      } as Message,
+    },
+    final: true,
+    metadata: {
+      coderAgent: stateChange,
+      model: 'unknown',
+      error: errorMessage,
+    },
+  });
+}