feat: wallet operations engine and encrypted storage with tests

src/lnurlcash/storageLock.ts

@@ -0,0 +1,14 @@
+// serializes a read-modify-write cycle across tabs: localStorage access
+// itself is per-tab synchronous, so two tabs interleaving read…write can
+// lose each other's records (worst case: a stale tab overwrites a freshly
+// persisted rotated note after its old k1 was burned). Falls back to
+// running unlocked where Web Locks is unavailable (plain-Node tests, very
+// old browsers).
+export const withStorageLock = <T>(
+  name: string,
+  fn: () => T | Promise<T>
+): Promise<T> => {
+  const locks = typeof navigator !== 'undefined' ? navigator.locks : undefined
+  if (locks) return locks.request(name, fn)
+  return Promise.resolve(fn())
+}