Set the capabilities fields to null when the model status is "after-download"?

[lozy219]

In the IDL of capabilities API, we have

  // Always null if available === "no"
  readonly attribute unsigned long? defaultTopK;
  readonly attribute unsigned long? maxTopK;
  readonly attribute float? defaultTemperature;
  readonly attribute float? maxTemperature;

Those optional attributes should also be set to null when available === "after-download" since the model is not ready yet.
It only becomes an issue after we migrated the sampling param config to the model.

[domenic]

Hmm.

The intention here is that this information is supposed to be available before the download, because it might impact whether a web developer wants to spend the user's bandwidth downloading the model, or not. This is discussed in https://github.com/WICG/translation-api#:~:text=This%20design%20means%20that%20the,mechanism%20that%20eagerly%20pushes%20updates.)

However, that's more important for questions like the supported languages. It's harder to imagine a web developer saying that they don't want to use the prompt API if maxTemperature only goes up to 1.0, or something like that.

So maybe we can keep the capabilities hyperparameters as null in the after-download state, even though we need to support languageAvailable() in that state.

What do you think?