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/useCommandsStore.ts

@@ -1,6 +1,6 @@
 import { create } from "zustand";
 import type { StoreApi, UseBoundStore } from "zustand";
-import { devtools, persist, createJSONStorage } from "zustand/middleware";
+import { devtools, persist } from "zustand/middleware";
 import { opencodeClient } from "@/lib/opencode/client";
 import {
   startConfigUpdate,
@@ -8,7 +8,7 @@ import {
   updateConfigUpdateMessage,
 } from "@/lib/configUpdate";
 import { emitConfigChange, scopeMatches, subscribeToConfigChanges } from "@/lib/configSync";
-import { getSafeStorage } from "./utils/safeStorage";
+import { createDeferredSafeJSONStorage } from "./utils/safeStorage";
 import { useProjectsStore } from "@/stores/useProjectsStore";
 import { runtimeFetch } from "@/lib/runtime-fetch";
 
@@ -427,7 +427,7 @@ export const useCommandsStore = create<CommandsStore>()(
       }),
       {
         name: "commands-store",
-        storage: createJSONStorage(() => getSafeStorage()),
+        storage: createDeferredSafeJSONStorage(),
         partialize: (state) => ({
           selectedCommandName: state.selectedCommandName,
         }),