Nextjs zustand

<objective> Implements Zustand v5 client-side state management in Next.js 16 App Router: the v5 currying syntax (`create<State>()((set) => ({...}))`), Context-based stores built with `createStore` from `zustand/vanilla` + `useRef` (required in App Router to avoid state leaking between requests — never a global store), and middleware composition (devtools → persist → immer, order-sensitive for TypeScript).

Covers skipHydration with the persist middleware plus manual rehydration in useEffect to avoid SSR mismatches, useShallow for array/object selectors, and SOLID file organization (store.ts, store-provider.tsx, use-store.ts). States explicitly that Zustand is Client-Components-only — never used in Server Components (fetch data directly there instead) and never used to persist auth tokens (use httpOnly cookies). Does not cover server state caching (see nextjs-tanstack-query for that). </objective>

Zustand for Next.js 16

Minimal, scalable state management with React 18+ useSyncExternalStore.

Agent Workflow (MANDATORY)

Before ANY implementation, use TeamCreate to spawn 3 agents:

1. fuse-ai-pilot:explore-codebase - Analyze existing stores and state patterns
2. fuse-ai-pilot:research-expert - Verify latest Zustand v5 docs via Context7/Exa
3. mcp__context7__query-docs - Check middleware and TypeScript patterns

After implementation, run fuse-ai-pilot:sniper for validation.

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Overview

When to Use

• Managing client-side state in Next.js App Router applications
• Need global state across Client Components only
• Persisting state to localStorage/sessionStorage
• Building UI state (modals, sidebars, theme, cart)
• Replacing React Context for complex state

Why Zustand v5

Feature	Benefit
Minimal API	Simple create() function, no boilerplate
React 18 native	useSyncExternalStore, no shims needed
TypeScript first	Full inference with currying pattern
Middleware stack	devtools, persist, immer composable
Bundle size	~2KB gzipped, smallest state library
No providers	Direct store access, no Context wrapper

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Critical Rules

1. Client Components ONLY - Never use Zustand in Server Components
2. Context pattern for App Router - Avoid global stores (request isolation)
3. useShallow for arrays/objects - Prevent unnecessary re-renders
4. skipHydration with persist - Required for SSR compatibility
5. Currying syntax v5 - create<State>()((set) => ({...}))
6. SOLID paths - Stores in modules/[feature]/src/stores/

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SOLID Architecture

Module Structure

Stores organized by feature module:

• modules/cores/stores/ - Shared stores (theme, ui)
• modules/auth/src/stores/ - Auth state
• modules/cart/src/stores/ - Cart state
• modules/[feature]/src/interfaces/ - Store types

File Organization

File	Purpose	Max Lines
store.ts	Store creation with create()	50
store.interface.ts	TypeScript interfaces	30
store-provider.tsx	Context provider (App Router)	40
use-store.ts	Custom hook with selector	20

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Key Concepts

Store Creation (v5 Syntax)

Double parentheses required for TypeScript inference. Currying pattern ensures full type safety.

Context-Based Stores

For Next.js App Router, wrap stores in Context to prevent request-sharing. Use createStore from zustand/vanilla with useRef for initialization.

Middleware Composition

Stack middlewares: devtools → persist → immer. Order matters for TypeScript types.

Hydration Handling

Use skipHydration: true with persist middleware. Manually rehydrate in useEffect to avoid SSR mismatches.

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Reference Guide

Need	Reference
Initial setup	installation.md
Store patterns	store-patterns.md
SSR/Hydration	hydration.md
Middleware	middleware.md
Next.js App Router	nextjs-integration.md
TypeScript	typescript.md
Slices pattern	slices.md
Auto selectors	auto-selectors.md
Reset state	reset-state.md
Subscribe API	subscribe-api.md
Testing	testing.md
Migration v4→v5	migration-v5.md

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Best Practices

1. Selector pattern - Always use useStore((s) => s.field) for performance
2. useShallow - Wrap array/object selectors to prevent re-renders
3. Separate stores - One store per domain (auth, cart, ui, theme)
4. Server data elsewhere - Use TanStack Query for server state
5. DevTools in dev only - Wrap devtools in process.env check
6. Partialize persist - Only persist necessary fields, never tokens

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Forbidden Patterns

Pattern	Reason	Alternative
Global stores in App Router	Request sharing between users	Context-based stores
Zustand in Server Components	No React hooks in RSC	Fetch data directly
Persisting auth tokens	Security vulnerability	httpOnly cookies
Without useShallow on objects	Excessive re-renders	useShallow(selector)
v4 syntax	TypeScript inference broken	v5 currying create<T>()()