Giving an AI Agent Write Access to Your App: Guardrails We Built for RobinReach's MCP Tools

A few months ago I wrote about building a production MCP server in Rails, the plumbing of exposing RobinReach's API as a set of MCP tools that Claude and other agents can call. That post was about connecting an AI agent to your app. This one is about the harder problem: what happens once it's connected and can actually do things, like publish to a client's Instagram, reply to a comment on their behalf, or schedule a week of content. The moment an agent has write access, "it works in the demo" s...