fix(context): Fix snapshot recovery across sessions. (#26939)

packages/core/src/utils/cryptoUtils.ts

@@ -0,0 +1,20 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { createHash } from 'node:crypto';
+
+/**
+ * Derives a stable, deterministic ID from a list of source IDs.
+ * Used for synthetic turns like summaries to ensure that re-summarizing the same
+ * content produces a consistent identity.
+ */
+export function deriveStableId(sourceIds: string[]): string {
+  const sortedIds = [...sourceIds].sort();
+  return createHash('sha256')
+    .update(sortedIds.join('|'))
+    .digest('hex')
+    .slice(0, 32);
+}