Harness Engineering for Reliable Coding Agents

Coding agents are moving from short, supervised edits toward tasks that span entire repositories and multiple sessions. The hard part has shifted from generating a patch to understanding the agent’s permitted scope and verifying that the evidence demonstrates the requested behavior. As a published researcher and VP of Technical Content at Educative, I’ve found that the hardest part of working with coding agents is rarely the model itself. The challenge is defining authority boundaries, building verification loops, and managing state around the model so its work remains reliable across multiple files and sessions. The course uses a fictional clinic-booking system across twenty-two lessons, beginning with a double-booking incident. You’ll diagnose why coding agents fail after the first hour. You’ll then design cross-session contracts, measure reliability costs, adjust control settings for a new model, and build a functional harness from scratch. As you complete the course, you will be able to start with one costly agent failure and add the smallest boundary, receipt, or test that makes it visible. You will have a mental model for reliable agent work and a runnable Wren harness that demonstrates the core runtime seams in code.