[WorldMaker]

Right, hence "closest to" in my description. Typescript's role ends at compile time and it can't/won't stop bad actors at runtime. Typescript tries to make it easier for good actors to do the right thing more of the time.

That said, the other benefit to using private symbols like this is that they are also easy to enforce at runtime, because symbol visibility is enforced at runtime (you can't create the same signal by hand somewhere else). It can be as easy as something like:

    console.assert(id.__brand__ === FooIdBrand)

(That still won't stop the determined hacker in the console dev tools, if they can see a symbol they can create a reference to it, defense in depth will always be a thing.)