This project links no libc and macOS links libc always, so a call that demands it compiles on a mac, passes every local lane, and refuses on both Linux runners -- the discovery order the fmt check already exists to prevent, and what zit#188 spent a red main on.

`zig build cross` compiles the CLI for x86_64-linux and aarch64-linux and runs nothing; gate depends on it. Verified to discriminate: reintroducing std.c.getenv fails cross while a plain macOS build still passes. check-in: 31c4850b95 user: dmestas tags: trunk