Building a Coding Agent Harness by Hand: Four Tools and a Loop | Harvard CS2680 Assignment 2
CS2680 Assignment 2 (Mads-Loop) has you write your own coding agent harness: with a fixed small model, qwen3.6-35b-a3b, it fixes real SWE-bench Pro issues inside Docker containers and logs every step in a required format. The assignment page says plainly not to trust the design it hands you, and some of the 10 tasks can't be solved. This post covers the spec, the places on the page worth doubting, the five places a harness most often breaks and how to handle each (with a snippet that has actually been run), how to build your own four-task eval set, and how to tell whether a task really is unsolvable. No official solution.