SaaS Application

Build a production-grade SaaS platform with multi-tenant account isolation, subscription billing, seat-based access, and detailed usage metering. Define clear data models for users, workspaces, entitlements, subscriptions, invoices, and usage events. Enforce role-based permissions across account management and administrative workflows. Include idempotent billing event processing, audit trails for permission and plan changes, observability for checkout and renewal failures, graceful handling of delinquent accounts, and a migration strategy for evolving pricing and entitlement rules without corrupting historical billing state.