One-way door check Some decisions are easy to reverse — you can change a UI component, rename a variable, or swap a utility function with no lasting consequences. These are two-way doors : walk through, and if it's wrong, walk back. Other decisions create gravity. Once traffic, users, or other code depends on them, changing course gets expensive. A database schema migration after launch. An API contract that external consumers rely on. An auth boundary that shapes your entire permission model. These are one-way doors . The most expensive mistakes in software aren't bugs. They're irreversible…