CanvasKit Layout Traps: The Unbounded Constraint Bug That Only Blanks Release Builds

I shipped eight card and casino games to my portfolio in a single commit — solitaire, roulette, video poker, slots, baccarat, keno, war, higher-lower. All client-side Flutter web, all free, all deployed to Firebase Hosting in one push. flutter analyze was clean. I read the diff twice. The build succeeded. I deployed. Then I opened /games/roulette on the live site and got a page with a header, a subtitle, a bankroll readout, a spin button — and a completely blank rectangle where the betting board should have been. No red error screen. No console exception. No 404. Just an empty region the size of the thing that was supposed to be there, on a page where everything else rendered perfectly. The cause was one enum value: CrossAxisAlignment.stretch on a Row that, four widgets up the tree, was sitting inside a scroll view. In debug that combination throws a loud, well-written framework error. In release the assertion that produces that error doesn't exist, so nothing throws at all — the framework computes with infinity and paints nothing. A layout contract violation is not a type error, and no amount of static analysis is going to find it for you. This post is that bug in full, the family of unbounded-constraint traps it belongs to, why debug builds give you a false sense of safety, and the verification discipline I now refuse to skip. Eight games shipped, one board rendered nothing The symptom is worth describing precisely, because it's what makes this class of bug so slow to diagnose. The route loaded. The page scaffold — nav, page header, back link, related-games strip — was all there and correct. Analytics fired the pageview. The bankroll, the chip selector and the spin control rendered. Only the number grid, the largest single widget on the page, drew nothing at all. The space it occupied wasn't even collapsed to zero; it was just empty. The browser console was clean. Not "clean apart from a warning" — genuinely empty. Chrome DevTools' Elements panel showed what it al