perf(stores): defer safeStorage writes off the interaction path (#1941)

* perf(stores): defer safeStorage writes off the interaction path

Session switches funnel every persisted store slice through safeStorage.setItem,
and doing those large JSON.stringify writes synchronously blocked the main
thread for over a second. Add a write-behind buffer that:

- Defers each setItem/removeItem to a later task via setTimeout(0) so the
  click-to-paint path is not blocked.
- Coalesces repeated writes to the same key into a single backing flush.
- Serves pending values from memory so read-after-write stays consistent
  within the deferral window.
- Flushes synchronously on pagehide/beforeunload/visibilitychange/freeze so
  deferred state survives tab close, reload, and the mobile freeze lifecycle.

Adds a test covering write deferral, coalescing, and pending read serving.

* fix(stores): defer persisted JSON serialization

* fix(stores): defer direct safeStorage writes

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/stores/permissionStore.ts

@@ -1,11 +1,11 @@
 import { create } from "zustand";
-import { devtools, persist, createJSONStorage } from "zustand/middleware";
+import { devtools, persist } from "zustand/middleware";
 import type { Session } from "@opencode-ai/sdk/v2/client";
 import {
     autoRespondsPermission,
     type PermissionAutoAcceptMap,
 } from "./utils/permissionAutoAccept";
-import { getSafeStorage } from "./utils/safeStorage";
+import { createDeferredSafeJSONStorage } from "./utils/safeStorage";
 import { getAllSyncSessions, getSyncChildStores } from "@/sync/sync-refs";
 import { opencodeClient } from "@/lib/opencode/client";
 import { respondToPermission } from "@/sync/session-actions";
@@ -201,7 +201,7 @@ const autoRespondsPermissionBySession = (
     });
 };
 
-const getStorage = () => createJSONStorage(() => getSafeStorage());
+const getStorage = () => createDeferredSafeJSONStorage();
 
 export const usePermissionStore = create<PermissionStore>()(
     devtools(