# Cart Module

Cart management, item availability checks.

## Responsibilities
- Add/remove items from cart
- Cart state (items grouped by store)
- Availability validation (item active, store active)
- Cart always reflects live prices — no price snapshots

## Key Rules
- One cart per user (user_id is unique on carts table)
- An item can only be in one cart at a time (item_id is unique on cart_items)
- Cart does NOT store prices — always fetched live from items table
- Removing unavailable items is the buyer's action, not automatic