I published a rule for picking AI tools. A commenter rewrote it into a better one.

A couple of weeks ago I published a post with a tidy rule in it. When you add capability to an AI coding agent, reach for the lightest option first: a procedure file before a CLI, a CLI before a heavier integration, and only build the heavy machinery once you've proven you'll reuse it. My whole case rested on context cost. The heavy options load a lot of definitions up front and carry them every turn, so starting light keeps the window clean. I still think the front half is right. But it isn't the rule I'd write now, because a reader took it apart in the comments and handed it back as something better. This post is about that exchange, because the rewrite was sharper than my original, and pretending I arrived at it alone would be both a lie and the less interesting story. The hole, found in one comment The first comment didn't argue with the rule. It walked straight to the blind spot. The moment a tool touches anything external or stateful, lightest-first reverses on you: a lightweight call that fails silently halfway through is harder to debug than a heavier tool that surfaces the failure cleanly. Pay the complexity up front. My first instinct was to defend, and I did, a little. I said we were measuring different things, that I'd optimized for context cost while they were optimizing for failure observability, both real, different axes. I held the line by pointing out you can wrap a lightweight call to fail loudly, so the cheap path stays open. That was true, and it was beside their point, and they didn't let me hide behind it. The question that moved the rule They asked one question that did more work than my entire post: what's your actual trigger for paying the complexity up front, the type of state, or the class of error? Sitting with that is where my own rule changed under me. The honest answer is state type, and the moment I said it out loud, context cost stopped being what the rule was about. What makes a failure expensive isn't the error. It's whether the op