add-global

name	add-global
description	Create a reactive global variable that derives from atoms with subscription support
aliases	["new-global","create-global"]

Add Global Skill

Usage

/add-global <globalName>

---

Step 1: Ask Questions

1. Global Purpose

What derived state does this global provide?
Brief description:

2. Source Atoms

Which atoms does this global derive from?
(List atom names from src/atoms/)

Examples: myInventoryAtom, myGardenAtom, weatherAtom

3. Derivation Logic

How is the global value computed from atoms?

A) Simple merge - Combine fields from multiple atoms
B) Transformation - Transform/filter atom data
C) Aggregation - Compute stats/totals from atoms
D) Complex - Multiple transformations

4. Update Sensitivity

Should subscribers react to every atom change?

A) Yes - Every change triggers update
B) No - Only meaningful changes (use subscribeStable)

5. Public API

Expose in window.Gemini.Globals?

A) Yes
B) No - Internal only

---

Step 2: Create Global File

Create src/globals/variables/<globalName>.ts

import { createReactiveGlobal } from '../core/reactive';
import { Store } from '../../atoms';
import type { GlobalVariable, Unsubscribe } from '../core/types';

// ─────────────────────────────────────────────────────────────────────────────
// Types
// ─────────────────────────────────────────────────────────────────────────────

export interface <GlobalName> {
    // Derived fields
    field1: string;
    field2: number;
}

// ─────────────────────────────────────────────────────────────────────────────
// Derivation
// ─────────────────────────────────────────────────────────────────────────────

async function derive<GlobalName>(): Promise<<GlobalName>> {
    const atom1 = await Store.select('sourceAtom1');
    const atom2 = await Store.select('sourceAtom2');

    return {
        field1: atom1?.value ?? 'default',
        field2: atom2?.count ?? 0,
    };
}

// ─────────────────────────────────────────────────────────────────────────────
// Reactive Global
// ─────────────────────────────────────────────────────────────────────────────

const <globalName>Global = createReactiveGlobal<<GlobalName>>({
    name: '<globalName>',
    atomKeys: ['sourceAtom1', 'sourceAtom2'],  // Atoms to watch
    derive: derive<GlobalName>,
});

// ─────────────────────────────────────────────────────────────────────────────
// Public API
// ─────────────────────────────────────────────────────────────────────────────

let instance: GlobalVariable<<GlobalName>> | null = null;

export function get<GlobalName>(): GlobalVariable<<GlobalName>> {
    if (!instance) {
        instance = <globalName>Global;
    }
    return instance;
}

---

Step 3: Register

In src/globals/index.ts

export { get<GlobalName> } from './variables/<globalName>';
export type { <GlobalName> } from './variables/<globalName>';

In src/api/index.ts (if public)

import { get<GlobalName> } from '../globals';

Globals: {
    // ... existing
    <globalName>: get<GlobalName>(),
}

---

Step 4: Validate

Structure

• File created in src/globals/variables/<name>.ts
• Type interface defined
• Derivation function implemented
• createReactiveGlobal() with correct atomKeys
• Lazy singleton getter exported

API

• get() returns current value
• subscribe(callback) receives all updates
• subscribeStable(callback) receives meaningful updates only
• destroy() is idempotent

Registration

• Exported from src/globals/index.ts
• Exposed in src/api/index.ts (if public)

---

Usage Patterns

Basic subscription

const global = get<GlobalName>();

// Get current value
const value = global.get();

// Subscribe to all changes
const unsub = global.subscribe((value) => {
    console.log('Updated:', value);
});

// Cleanup
unsub();

Stable subscription (less frequent)

const unsub = global.subscribeStable((value) => {
    // Only fires on meaningful changes
    updateUI(value);
});

In components/features

const cleanups: (() => void)[] = [];

function start(): void {
    const unsub = get<GlobalName>().subscribe((value) => {
        onValueChange(value);
    });
    cleanups.push(unsub);
}

function stop(): void {
    cleanups.forEach(fn => fn());
    cleanups.length = 0;
}

---

References

• Rules: .claude/rules/state/globals.md
• Existing globals: src/globals/variables/
• Core: src/globals/core/