gap-trap's "Proven Red" gate runs every new test against the old code and fails when it passes.

pliablepixels/gap-trap, created September 13 and at 78 stars, installs four things in a repo: contracts with approved and forbidden patterns per area, Proven Red, ratchets where lint backlog and 400-line file counts may go down but never up, and playbooks (GitHub). Proven Red is the mechanical version of watching the guard fail first: a CI job that checks out pre-change code, runs the new test against it, and fails the build if the test passes there. /gap-trap setup proves each gate red before committing it. Node and Python repos embed the gates in the test suite; Go, Rust, Java, Ruby, .NET, PHP, Swift and C++ use shell checks needing only git, grep, awk and a test command. I've had this discipline as a rule for a year and never had CI enforce it.