Small FE improvements

frontend/sync-client/src/persistence/persistence.ts

@@ -1,3 +1,7 @@
+/** save() atomically replaces the entire value and resolves only after both the
+ * data and its directory entry are durable across power loss. Failed saves must
+ * leave either complete value readable; callers retain their recovery journal.
+ */
 export interface PersistenceProvider<T> {
     load: () => Promise<T | undefined>;
     save: (data: T) => Promise<void>;