Nit: the fallback object is allocated *after* the implementation runs (which is invoked as a plain `[[Call]]` with `callframe->thisValue()`), so for `new (jest.fn(function(){ this.x = 42 }))()` the `this.x = 42` lands on the wrong object and the returned instance is an empty `{}` — Jest yields `{x: 42}`. Not blocking — this is still a strict improvement over the crash — but the "matching ordinary `[[Construct]]` semantics" claim doesn't hold for the constructor‑assigns‑to‑`this` pattern; a fulle