KiCad Prism's Nix package can now refill copper zones and upgrade board files inside its pinned build environment. A copper zone is a filled area that carries power or ground around traces. Every design bundle containing one had failed because Prism launched an isolated Python interpreter that couldn't import pcbnew, KiCad's scripting library.
The fix creates a Python 3.14 environment with KiCad's own packages linked through a .pth file, then points Prism at that interpreter. The detail matters: Prism invokes Python with isolated mode, which ignores the usual PYTHONPATH setting. The package's install check now imports pcbnew the same way the production command does, so a missing library fails while the package is built instead of when a board reaches the renderer.
Board automation often breaks on dependencies that a graphical KiCad installation supplies silently. This patch turns one of those workstation assumptions into declared build input. If the check remains stable across KiCad updates, teams can treat zone refill as a reviewable pipeline step and reserve the desktop application for inspecting the resulting geometry.