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A class constructor's `return expr` was evaluated and dropped, so `new C()` answered the constructed instance even where Node answers the returned object (`if (C.instance) return C.instance;` built a second instance). A return that yields an instance of the class itself stores it in a per-class result slot, read and cleared by one helper at every construction site (direct new, class values, the checked dynamic construction dispatchers, record-to-class coercion). A return of any other object refuses with SC1090 (compile time in TypeScript, a deferred fence in JavaScript); a JavaScript value typed only at run time is tested when it returns. super() into a class that can return an existing instance refuses, since Node would rebind the subclass's this. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>