diff --git a/src/lnurlcash/storageLock.test.ts b/src/lnurlcash/storageLock.test.ts
new file mode 100644
index 0000000..a6a9afb
--- /dev/null
+++ b/src/lnurlcash/storageLock.test.ts
@@ -0,0 +1,30 @@
+import {describe, expect, it, vi} from 'vitest'
+
+import {withStorageLock} from './storageLock'
+
+describe('withStorageLock fallback', () => {
+  it('runs unlocked when Web Locks are unavailable without promising serialization', async () => {
+    vi.stubGlobal('navigator', {})
+    const entered: string[] = []
+    let releaseFirst: (() => void) | undefined
+
+    try {
+      const first = withStorageLock('registry', async () => {
+        entered.push('first')
+        await new Promise<void>((resolve) => {
+          releaseFirst = resolve
+        })
+      })
+      const second = withStorageLock('registry', () => {
+        entered.push('second')
+      })
+
+      await second
+      expect(entered).toEqual(['first', 'second'])
+      releaseFirst?.()
+      await first
+    } finally {
+      vi.unstubAllGlobals()
+    }
+  })
+})
diff --git a/src/lnurlcash/storageLock.ts b/src/lnurlcash/storageLock.ts
index dc96281..16ff91b 100644
--- a/src/lnurlcash/storageLock.ts
+++ b/src/lnurlcash/storageLock.ts
@@ -3,12 +3,13 @@
 // 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> => {
+// old browsers). That fallback provides no cross-tab serialization
+// guarantee; the promise hop only normalizes synchronous callback errors.
+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())
+  if (locks) return locks.request(name, () => Promise.resolve().then(fn))
+  return Promise.resolve().then(fn)
 }
+
+export const storageLocksAvailable = (): boolean =>
+  typeof navigator !== 'undefined' && navigator.locks !== undefined