Design a customer-service AI agent with tools and guardrails

You built a small conversational agent with two tools for the take-home. Now design the real thing: a platform that runs AI agents for many consumer brands, over chat and voice, that answer from each brand's help content and take actions in the brand's systems (order lookups, returns, refunds, subscription changes). Cover the agent loop, how business rules such as identity checks, refund limits and confirmations are enforced, exactly-once actions, human handoff, voice latency, per-brand configuration and safe rollout.