state-management

State Management Skill

Client state management standards and best practices. The universal guidance (local-vs-global decisions, store structure, selectors, performance) applies to any store library; the concrete code examples use Zustand.

When to Apply

• Creating new state stores
• Sharing state between components
• State architecture decisions
• Performance optimization for state

---

State Category Guidelines

Category	Solution	Use When
Local UI	useState	Single component, simple state
Shared UI	Zustand store	Multiple components need same data
Server data	React Query / SWR	API data with caching needs
Form state	useState / form library	Form inputs, validation
URL state	useSearchParams	Filter/sort params, shareable URLs

---

Zustand Store Standards

Store Structure

Element	Requirement
Interface	Define typed state + actions interface
State	Group related state together
Actions	Define all mutations as functions
Naming	use[Domain]Store convention

Store Design Principles

Principle	Description
Single responsibility	One store per domain (projects, UI, settings)
Flat structure	Avoid deeply nested state
Immutable updates	Always return new objects
Colocated actions	Keep actions inside store definition

---

Selector Best Practices

Selection Rules

Rule	Reason
Select minimal data	Reduces re-renders
Use shallow for objects	Prevents unnecessary updates
Memoize derived data	Use useMemo for computed values
Avoid selecting entire store	Causes re-render on any change

Selector Patterns

Pattern	Use Case
Single value	(state) => state.count
Multiple values	(state) => ({ a: state.a, b: state.b }), shallow
Derived value	useMemo outside store

---

Middleware Usage

Middleware	Purpose	When to Use
persist	LocalStorage persistence	User preferences, settings
devtools	Redux DevTools integration	Development debugging
immer	Immutable updates	Complex nested state
subscribeWithSelector	Granular subscriptions	Performance optimization

---

Store Organization

File Structure

src/stores/
├── index.ts           # Re-exports all stores
├── projectStore.ts    # Domain-specific store
├── uiStore.ts         # UI state (modals, panels)
└── settingsStore.ts   # User preferences

Store Separation Guidelines

Store Type	Contains
Domain store	Business entities, selections
UI store	Modal states, panel visibility, loading
Settings store	User preferences, persisted config

---

Performance Guidelines

DO

• Select only needed state slices
• Use shallow equality for object selections
• Define actions inside store (stable references)
• Split large stores by domain
• Use subscribeWithSelector for side effects

DON'T

• Select entire store object
• Create new objects in selectors without shallow
• Put derived/computed state in store
• Call actions during render phase
• Create deeply nested store structure

---

Anti-Patterns

Anti-Pattern	Problem	Solution
Giant store	Hard to maintain, performance issues	Split by domain
Computed in store	Stale data, extra complexity	Use useMemo
Prop drilling	Bypasses store benefits	Use store directly
Store in useState	Loses reactivity	Use store hook
No TypeScript	Runtime errors	Define interfaces

---

Decision Matrix

Scenario	Recommended Solution
Form input state	useState
Modal open/close	useState or UI store
Selected item (shared)	Domain store
User preferences	Persisted store
API response data	Store + service function
Computed/derived data	useMemo from store values
Global loading state	UI store

---

Example: Zustand Store Patterns (illustrative)

Illustrative — these are one team's concrete Zustand conventions shown as an example. Substitute your store library's equivalents (Redux Toolkit, Jotai, Pinia, signals, etc.). The decision matrix and selector/performance guidance above are the reusable, library-agnostic part.

Store Files (<your-stores-module>/)

Store	Persist	Purpose
workspaceStore.ts	Yes (scaffolding-workspaces)	Projects/workspaces, active selection
taskStore.ts	No	Task CRUD, SSE updates, agent statuses
authStore.ts	Yes (auth-storage)	GitHub OAuth state, user profile

Type Pattern: Separate State & Actions

Every store defines type XxxState and type XxxActions, then exports the combined type:

type WorkspaceState = {
  workspaces: Workspace[];
  activeWorkspace: Workspace | null;
};
type WorkspaceActions = {
  addWorkspace: (pathOrWorkspace: string | Workspace) => void;
  removeWorkspace: (path: string) => Promise<void>;
  setActiveWorkspace: (path: string) => void;
  loadFromApi: () => Promise<void>;
};
export type WorkspaceStore = WorkspaceState & WorkspaceActions;

Persist Middleware with partialize

Persisted stores use partialize to exclude actions and transient state from storage:

export const useWorkspaceStore = create<WorkspaceStore>()(
  persist(
    (set, get) => ({ /* state + actions */ }),
    {
      name: 'scaffolding-workspaces',
      partialize: (state) => ({
        workspaces: state.workspaces,
        activeWorkspace: state.activeWorkspace,
      }),
    }
  )
);

Hook Wrappers with useShallow (<your-hooks-module>/)

Stores are consumed through hook wrappers that use useShallow to prevent re-renders:

import { useWorkspaceStore } from '../stores/workspaceStore';
import { useShallow } from 'zustand/shallow';

export function useWorkspace() {
  return useWorkspaceStore(
    useShallow((state) => ({
      workspaces: state.workspaces,
      activeWorkspace: state.activeWorkspace,
      addWorkspace: state.addWorkspace,
      // ... selected fields only
    }))
  );
}

API Sync Pattern (loadFromApi)

Stores hydrate from localStorage first, then enrich from API:

1. persist middleware loads cached state from localStorage on mount
2. loadFromApi() fetches from backend, merges fields (id, github_url, role) into existing entries
3. Failures are silently caught - localStorage data still works offline

SSE Update Pattern (taskStore)

Non-persisted stores receive real-time updates from Server-Sent Events:

• addTask(task) - deduplicates before prepending to list
• updateTask(task) - replaces full task object in list and currentTask
• updateTaskPartial(id, updates) - merges partial fields from SSE completion events
• updateAgentStatus(taskId, status) - tracks per-agent progress within a task

Error Handling in Stores

Stores use extractErrorMessage(err, fallbackMsg) utility and store errors in state:

catch (err) {
  const message = extractErrorMessage(err, 'Failed to fetch tasks');
  set({ error: message, isLoading: false });
}

For expected errors (e.g., 409 conflict on cancel), check AxiosError status before setting error state.