Tailwind Guides #1: What Actually Broke Migrating to v4

I was halfway through shipping a component update when v4 dropped. My design system, 7onic, has to work with both Tailwind v3 and v4 — same components, same token source, two different output formats. So my reaction to the v4 announcement was less "exciting new features" and more "great, another output target to maintain." I read the migration guide. It covered the syntax changes fine. What it didn't cover was that three of those changes would silently break things in ways that produced zero er...