CircuitPilot found a dangerous gap between its AI planner and its printed circuit board (PCB) editor. The planner expressed component positions and track widths in millimeters, while the editor expected mils, where one mil is one thousandth of an inch. Passing the numbers through unchanged shrank components, tracks, and vias by 25.4x even though the 45 millimeter board outline stayed correct.
The uncomfortable detail is that quantity readback and design rule checking (DRC), the automated check for spacing and manufacturing-rule violations, could still pass. Those checks proved that the malformed board was internally consistent. They didn't prove that the agent's intended geometry reached the editor unchanged. CircuitPilot now converts units in one place and runs a regression test across that boundary.
AI board tools need tests for meaning, not only legal geometry. A useful test should place a known part at a known metric coordinate, write the board, read it back, and compare the physical distance. If an agent can produce a board that is valid at the wrong scale, DRC cannot be the final release gate.