refactor: Centralize session ID generation and propagation

packages/core/src/utils/session.ts

@@ -0,0 +1,9 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { randomUUID } from 'crypto';
+
+export const sessionId = randomUUID();