feat: add persisted owner guards and events

src/lnurlcash/storage/currentOwner.ts

@@ -0,0 +1,20 @@
+// Mutators must not let a still-running old tab overwrite namespaces after a
+// successor has installed its saved-key owner marker. Ownerless data may only
+// move through explicit migration APIs after their own proof checks succeed.
+
+import {savedKeyOwnerId} from '../keys'
+
+export class WalletOwnerMismatchError extends Error {
+  override readonly name = 'WalletOwnerMismatchError'
+  constructor() {
+    super('The active wallet owner no longer matches the saved wallet.')
+  }
+}
+
+export const savedKeyOwnerAllows = (ownerId: string): boolean => {
+  return savedKeyOwnerId() === ownerId
+}
+
+export const assertSavedKeyOwner = (ownerId: string): void => {
+  if (!savedKeyOwnerAllows(ownerId)) throw new WalletOwnerMismatchError()
+}

src/lnurlcash/storage/walletOwnerEvents.ts

@@ -0,0 +1,17 @@
+// Storage events only wake an owning store to reread its saved-key marker.
+// Their payload may be stale when writes arrive faster than delivery.
+
+export const LINKING_KEY_STORAGE_KEY = 'sattle_linking_key'
+
+// Each subscription binds its own storage listener and removes exactly it on
+// unsubscribe: no shared reference counting, so an abandoned subscriber can
+// never keep another subscriber's window listener (or runtime) alive.
+export const onSavedKeyStorageChange = (listener: () => void): (() => void) => {
+  const target = typeof window === 'undefined' ? null : window
+  const onStorage = (event: StorageEvent): void => {
+    if (event.key !== LINKING_KEY_STORAGE_KEY && event.key !== null) return
+    listener()
+  }
+  target?.addEventListener('storage', onStorage)
+  return () => target?.removeEventListener('storage', onStorage)
+}