Where are update’s validation rules defined and executed?

[IGassmann]

Where can validation rules for a given change be implemented in LiveStore, and where do they get executed (server, client)? For instance, how could such validation rules be implemented:

• Global Uniqueness Checks: Checking if an email address is already taken across the entire user base.
• Inventory Levels: Checking if stock is available before confirming an order.
• Complex Permissions/ACLs: Validating if user A has permission based on rules involving groups or data user B owns, which user A might not have loaded.
• Domain Rules: Validating if a change can be made only if X or Y is true in the current state.