The gbrain-missing test appended the host PATH (and a hardcoded /opt/homebrew/bin) to the fixture PATH, so on any machine with a real gbrain installed the 'missing' case saw it, exited 0 instead of 2, and could never fail where the bug exists — a false green for a whole machine class. The fixture now keeps only root-owned OS dirs on the child PATH, and a new determinism check plants a host-like gbrain to prove it is unreachable.
Absorbed from PR #2615 with authorship preserved; the PR-thread liveness screenshot (docs/images/gstack-pr-liveness-2255.png) is dropped — referenced by nothing in the tree.
Fixes#2255
Co-authored-by: CommandCodeBot <noreply@commandcode.ai>
