06 / 08
The design could not be built where it was going.
Found before a line of code was written. One feature, two screens and a button.
npx halfcycle The part of the screen it was meant to live in cannot change the content it would have had to replace.
Would a code review have caught it?
Yes, eventually. By the person building it, halfway through, after the work had already been handed out.
Not every problem on these cards would have reached a user. This one would have cost time instead, and it would have cost it at the worst point.
The design said the restored version should appear in a particular part of the page: a panel that sits alongside the document. That panel is a separate slot. It can add things next to the document, but it cannot change the document itself. And the content it would have needed to replace arrives from the server already rendered, not in the form the design assumed it could work with.
In other words, the plan described something that could not be built where it said it would go. No test fails on a plan. A reviewer reading the design on its own would not see it either, because the design agrees with itself. You only find it by knowing, or going to check, what that part of the page is actually allowed to do.
Left alone, the person building it would have found out halfway through, after the work had been split up and handed out. The design would then have gone back to the start with somebody already in the middle of a task. That is the expensive way to learn about a constraint.
Read the other seven, or the same argument in general terms: why an agent reviewing its own work is not enough.