tl;dr: Copperhead is an open-source AI agent that designs and verifies KiCad PCBs through an eight-stage pipeline (brief → spec → architecture → BOM → schematic → layout → gerbers → firmware → dev plan), gating each stage on validated artifacts and clean ERC/DRC checks. It makes surgical edits to KiCad s-expression files rather than regenerating them, refuses to run on dirty git trees or violate documented constraints, and aims to prevent the design drift that causes costly board respins. The CLI is free (Apache-2.0, BYO model key); hosted cloud, team, and enterprise tiers start at $49/user/month.