13 days late but for posterity:

Yes. Not Wanting To Do That was the motivating factor for coming up with this approach :D

8 days late but for posterity:

So far I've only ever been using a private symbol that only exists within the codebase in question (and is then exported to other parts of said codebase as required).

If I ever decide to generalise the approach a bit, I'll hopefully remember to do precisely what you describe.

Possibly with the addition of providing an "I am overriding this deliberately" flag that blows up if it doesn't already have said symbol.

But for the moment, the maximally dumbass approach in my original post is DTRT for me so far.

Oh my word.

    const defer = f => ({ [Symbol.dispose]: f })

    using defer(() => cleanup())

I regularly add Symbol based features to JS libraries I'm using (named methods are riskier, of course)

    import { SomeStreamClass as SomeStreamClass_ } from "some/library"
    export class SomeStreamClass extends SomeStreamClass_ {
      [someSymbol] (...) { ... }
      ...
    }

It's been working excellently for me so far though.

If you want to play with this, Bun 1.0.23+ seems to already have support: https://github.com/oven-sh/bun/discussions/4325