Give a coding agent a failing test and it fixes itself. Give it a stack trace, a type error, a red CI log, and it reads the signal, reasons about the cause, and corrects. That loop is the whole reason agents feel autonomous on the backend.
On the UI it falls apart.
The agent edits some CSS, sees nothing, and tells you it "looks great." It has no eyes on the result. A blind reviewer rubber-stamps everything, and an agent reviewing its own UI change with no picture of it is exactly that. So it ships, and you find the regression later: a button that shrank two pixels, a card that reflowed on mobile, a shadow that vanished in dark mode. Nothing your test suite asserts on. Nothing the agent could see.
I've been building visual testing for this exact gap, and the fix turned out to be boring. Give the agent the actual diff.
The missing piece was never a smarter model
