TL;DR A codebase can be read as a field that attracts future changes, and a pull request can be read as a force applied to that field. A good field makes good changes easier to make. A bad field repeatedly makes bad shortcuts look natural. In an era where AI can produce PRs quickly, this attraction becomes stronger. I call the practice of designing where future changes are pulled Attractor Engineering . CI/CD, tests, reviews, and harnesses can be read as dissipative systems: they remove unwanted force and shape the trajectory. ArchSig, or Architecture Signature, is a tool for observing that trajectory along multiple axes. The first half of this article is written for practitioners: it explains the intuition in terms of codebases, PRs, review, CI, and AI-assisted development. The second half is more mathematical: it connects the same intuition to AAT, Architecture Signature, Lean formalization, and finite counterexamples. The First Discovery The starting point was a simple thought experiment.…