Where does state live?

State is the data that changes while your app runs: what's in the cart, which hall is open, whether a menu is shown.

Keep it as local as you can, and share it only as widely as needed. State that the whole app can change needs one clear home, or you'll never know who changed it.

• Local state → a ref inside one component.
• Parent and child → props down, events up.
• A deep tree of components → provide / inject.
• Shared across the whole app → a Pinia store.