Modernizing Legacy Systems Using Agent Harnesses TDD and the Seam Model

Over the past few months, I’ve been investing a lot of time building agentic development workflows for real production environments. Not only prompts. Actual operational environments around agents. Things like skills, execution tooling, validation layers, testing flows, memory handling, Git integrations, and constrained execution paths. One thing became very clear very quickly. Using agents in legacy or mission critical systems without a proper harness can become dangerous surprisingly fast. Esp