Ensure Vue composables, reactive state, and side effects are properly scoped within Vue's execution context to prevent SSR failures, memory leaks, and shared state across requests. **Key Rules:** 1. **Never call composables at module top-level** - Composables must be called within ` ``` ✅ **Correct - Proper context usage:** ```ts // utils/api.ts export default defineNuxtPlugin((nuxtApp) => { const { session } = useUserSession() // Called within plugin context }) ``` ✅ **Correct - Side effects in lifecycle hooks:** ```vue ``` This prevents SSR hydration mismatches, memory leaks, and ensures proper cleanup of resources across the Vue component lifecycle.